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AppArmor Admin Guide
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4.6 Two Methods of Profiling

Given the syntax for AppArmor profiles in Section 2.0, Profile Components and Syntax, you could create profiles without using the tools. However, the effort involved would be substantial. To avoid such a hassle, use the AppArmor tools to automate the creation and refinement of profiles.

There are two ways to approach AppArmor profile creation. Tools are available for both methods.

Stand-Alone Profiling

A method suitable for profiling small applications that have a finite run time, such as user client applications like mail clients. For more information, refer to Section 4.6.1, Stand-Alone Profiling.

Systemic Profiling

A method suitable for profiling large numbers of programs all at once and for profiling applications that may run for days, weeks, or continuously across reboots, such as network server applications like Web servers and mail servers. For more information, refer to Section 4.6.2, Systemic Profiling.

Automated profile development becomes more manageable with the AppArmor tools:

  1. Decide which profiling method suits your needs.

  2. Perform a static analysis. Run either aa-genprof or aa-autodep, depending on the profiling method chosen.

  3. Enable dynamic learning. Activate learning mode for all profiled programs.

4.6.1 Stand-Alone Profiling

Stand-alone profile generation and improvement is managed by a program called aa-genprof. This method is easy because aa-genprof takes care of everything, but is limited because it requires aa-genprof to run for the entire duration of the test run of your program (you cannot reboot the machine while you are still developing your profile).

To use aa-genprof for the stand-alone method of profiling, refer to aa-genprof—Generating Profiles.

4.6.2 Systemic Profiling

This method is called systemic profiling because it updates all of the profiles on the system at once, rather than focusing on the one or few targeted by aa-genprof or stand-alone profiling. With systemic profiling, profile construction and improvement are somewhat less automated, but more flexible. This method is suitable for profiling long-running applications whose behavior continues after rebooting or a large number of programs all at once.

Build an AppArmor profile for a group of applications as follows:

  1. Create profiles for the individual programs that make up your application.

    Although this approach is systemic, AppArmor only monitors those programs with profiles and their children. To get AppArmor to consider a program, you must at least have aa-autodep create an approximate profile for it. To create this approximate profile, refer to aa-autodep—Creating Approximate Profiles.

  2. Put relevant profiles into learning or complain mode.

    Activate learning or complain mode for all profiled programs by entering aa-complain /etc/apparmor.d/* in a terminal window while logged in as root. This functionality is also available through the YaST Profile Mode module, described in Section 3.6.2, Changing the Mode of Individual Profiles.

    When in learning mode, access requests are not blocked even if the profile dictates that they should be. This enables you to run through several tests (as shown in Step 3) and learn the access needs of the program so it runs properly. With this information, you can decide how secure to make the profile.

    Refer to aa-complain—Entering Complain or Learning Mode for more detailed instructions for using learning or complain mode.

  3. Exercise your application.

    Run your application and exercise its functionality. How much to exercise the program is up to you, but you need the program to access each file representing its access needs. Because the execution is not being supervised by aa-genprof, this step can go on for days or weeks and can span complete system reboots.

  4. Analyze the log.

    In systemic profiling, run aa-logprof directly instead of letting aa-genprof run it (as in stand-alone profiling). The general form of aa-logprof is:

    aa-logprof [ -d /path/to/profiles ] [ -f /path/to/logfile ]

    Refer to aa-logprof—Scanning the System Log for more information about using aa-logprof.

  5. Repeat Step 3 and Step 4.

    This generates optimum profiles. An iterative approach captures smaller data sets that can be trained and reloaded into the policy engine. Subsequent iterations generate fewer messages and run faster.

  6. Edit the profiles.

    You might want to review the profiles that have been generated. You can open and edit the profiles in /etc/apparmor.d/ using vim.

  7. Return to enforce mode.

    This is when the system goes back to enforcing the rules of the profiles, not just logging information. This can be done manually by removing the flags=(complain) text from the profiles or automatically by using the aa-enforce command, which works identically to the aa-complain command, except it sets the profiles to enforce mode. This functionality is also available through the YaST Profile Mode module, described in Section 3.6.2, Changing the Mode of Individual Profiles.

    To ensure that all profiles are taken out of complain mode and put into enforce mode, enter aa-enforce /etc/apparmor.d/*.

  8. Rescan all profiles.

    To have AppArmor rescan all of the profiles and change the enforcement mode in the kernel, enter rcapparmor restart.

4.6.3 Summary of Profiling Tools

All of the AppArmor profiling utilities are provided by the apparmor-utils RPM package and are stored in /usr/sbin. Each tool has a different purpose.

aa-autodep—Creating Approximate Profiles

This creates an approximate profile for the program or application selected. You can generate approximate profiles for binary executables and interpreted script programs. The resulting profile is called approximate because it does not necessarily contain all of the profile entries that the program needs to be properly confined by AppArmor. The minimum aa-autodep approximate profile has at least a base include directive, which contains basic profile entries needed by most programs. For certain types of programs, aa-autodep generates a more expanded profile. The profile is generated by recursively calling ldd(1) on the executables listed on the command line.

To generate an approximate profile, use the aa-autodep program. The program argument can be either the simple name of the program, which aa-autodep finds by searching your shell's path variable, or it can be a fully qualified path. The program itself can be of any type (ELF binary, shell script, Perl script, etc.). aa-autodep generates an approximate profile to improve through the dynamic profiling that follows.

The resulting approximate profile is written to the /etc/apparmor.d directory using the AppArmor profile naming convention of naming the profile after the absolute path of the program, replacing the forward slash (/) characters in the path with period (.) characters. The general form of aa-autodep is to enter the following in a terminal window when logged in as root:

aa-autodep [ -d /path/to/profiles ] [program1 program2...]

If you do not enter the program name or names, you are prompted for them. /path/to/profiles overrides the default location of /etc/apparmor.d, should you keep profiles in a location other than the default.

To begin profiling, you must create profiles for each main executable service that is part of your application (anything that might start without being a child of another program that already has a profile). Finding all such programs depends on the application in question. Here are several strategies for finding such programs:

Directories

If all the programs to profile are in one directory and there are no other programs in that directory, the simple command aa-autodep /path/to/your/programs/* creates basic profiles for all programs in that directory.

ps command

You can run your application and use the standard Linux ps command to find all processes running. Then manually hunt down the location of these programs and run the aa-autodep for each one. If the programs are in your path, aa-autodep finds them for you. If they are not in your path, the standard Linux command find might be helpful in finding your programs. Execute find / -name 'my_application' -print to determine an application's path (my_application being an example application). You may use wild cards if appropriate.

aa-complain—Entering Complain or Learning Mode

The complain or learning mode tool (aa-complain) detects violations of AppArmor profile rules, such as the profiled program accessing files not permitted by the profile. The violations are permitted, but also logged. To improve the profile, turn complain mode on, run the program through a suite of tests to generate log events that characterize the program's access needs, then postprocess the log with the AppArmor tools to transform log events into improved profiles.

Manually activating complain mode (using the command line) adds a flag to the top of the profile so that /bin/foo becomes /bin/foo flags=(complain). To use complain mode, open a terminal window and enter one of the following lines as root:

  • If the example program (program1) is in your path, use:

    aa-complain [program1 program2 ...]
  • If the program is not in your path, specify the entire path as follows:

    aa-complain /sbin/program1
    
  • If the profiles are not in /etc/apparmor.d, use the following to override the default location:

    aa-complain /path/to/profiles/ program1
         
  • Specify the profile for program1 as follows:

    aa-complain /etc/apparmor.d/sbin.program1

Each of the above commands activates the complain mode for the profiles or programs listed. If the program name does not include its entire path, aa-complain searches $PATH for the program. For instance, aa-complain /usr/sbin/* finds profiles associated with all of the programs in /usr/sbin and puts them into complain mode. aa-complain /etc/apparmor.d/* puts all of the profiles in /etc/apparmor.d into complain mode.

HINT: Toggling Profile Mode with YaST

YaST offers a graphical front-end for toggling complain and enforce mode. See Section 3.6.2, Changing the Mode of Individual Profiles for information.

aa-enforce—Entering Enforce Mode

The enforce mode detects violations of AppArmor profile rules, such as the profiled program accessing files not permitted by the profile. The violations are logged and not permitted. The default is for enforce mode to be enabled. To log the violations only, but still permit them, use complain mode. Enforce toggles with complain mode.

Manually activating enforce mode (using the command line) adds a flag to the top of the profile so that /bin/foo becomes /bin/foo flags=(enforce). To use enforce mode, open a terminal window and enter one of the following lines as root.

  • If the example program (program1) is in your path, use:

    aa-enforce [program1 program2 ...]
  • If the program is not in your path, specify the entire path, as follows:

    aa-enforce /sbin/program1
  • If the profiles are not in /etc/apparmor.d, use the following to override the default location:

    aa-enforce /path/to/profiles/program1
  • Specify the profile for program1 as follows:

    aa-enforce /etc/apparmor.d/sbin.program1

Each of the above commands activates the enforce mode for the profiles and programs listed.

If you do not enter the program or profile names, you are prompted to enter one. /path/to/profiles overrides the default location of /etc/apparmor.d.

The argument can be either a list of programs or a list of profiles. If the program name does not include its entire path, aa-enforce searches $PATH for the program.

HINT: Toggling Profile Mode with YaST

YaST offers a graphical front-end for toggling complain and enforce mode. See Section 3.6.2, Changing the Mode of Individual Profiles for information.

aa-genprof—Generating Profiles

aa-genprof is AppArmor's profile generating utility. It runs aa-autodep on the specified program, creating an approximate profile (if a profile does not already exist for it), sets it to complain mode, reloads it into AppArmor, marks the log, and prompts the user to execute the program and exercise its functionality. Its syntax is as follows:

aa-genprof [ -d /path/to/profiles ]  program

To create a profile for the the Apache Web server program httpd2-prefork, do the following as root:

  1. Enter rcapache2 stop.

  2. Next, enter aa-genprof httpd2-prefork.

    Now aa-genprof does the following:

    1. Resolves the full path of httpd2-prefork using your shell's path variables. You can also specify a full path. On openSUSE, the default full path is /usr/sbin/httpd2-prefork.

    2. Checks to see if there is an existing profile for httpd2-prefork. If there is one, it updates it. If not, it creates one using the aa-autodep as described in Section 4.6.3, Summary of Profiling Tools.

    3. Puts the profile for this program into learning or complain mode so that profile violations are logged but are permitted to proceed. A log event looks like this (see /var/log/audit/audit.log):

      type=APPARMOR_ALLOWED msg=audit(1189682639.184:20816): operation="file_mmap" requested_mask="r" denied_mask="r" name="/srv/www/htdocs/index.html" pid=27471 profile="null-complain-profile"
      

      If you are not running the audit daemon, the AppArmor events are logged to /var/log/messages:

      Sep 13 13:20:30 K23 kernel: audit(1189682430.672:20810): operation="file_mmap" requested_mask="r" denied_mask="r" name="/srv/www/htdocs/phpsysinfo/templates/bulix/form.tpl" pid=30405 profile="/usr/sbin/httpd2-prefork///phpsysinfo/"

      They also can be viewed using the dmesg command:

      audit(1189682430.672:20810): operation="file_mmap" requested_mask="r" denied_mask="r" name="/srv/www/htdocs/phpsysinfo/templates/bulix/form.tpl" pid=30405 profile="/usr/sbin/httpd2-prefork///phpsysinfo/"
    4. Marks the log with a beginning marker of log events to consider. For example:

      Sep 13 17:48:52 figwit root: GenProf: e2ff78636296f16d0b5301209a04430d
  3. When prompted by the tool, run the application to profile in another terminal window and perform as many of the application functions as possible. Thus, the learning mode can log the files and directories to which the program requires access in order to function properly. For example, in a new terminal window, enter rcapache2 start.

  4. Select from the following options that are available in the aa-logprof terminal window after you have executed the program function:

    • S runs aa-logprof on the system log from where it was marked when aa-genprof was started and reloads the profile. If system events exist in the log, AppArmor parses the learning mode log files. This generates a series of questions that you must answer to guide aa-genprof in generating the security profile.

    • F exits the tool and returns to the main menu.

    NOTE: If requests to add hats appear, proceed to Section 5.0, Profiling Your Web Applications Using ChangeHat.

  5. Answer two types of questions:

    • A resource is requested by a profiled program that is not in the profile (see Example 4-1).

    • A program is executed by the profiled program and the security domain transition has not been defined (see Example 4-2).

    Each of these categories results in a series of questions that you must answer to add the resource or program to the profile. Example 4-1 and Example 4-2 provide examples of each one. Subsequent steps describe your options in answering these questions.

    • Dealing with execute accesses is complex. You must decide how to proceed with this entry regarding which execute permission type to grant to this entry:

      Example 4-1 Learning Mode Exception: Controlling Access to Specific Resources

      Reading log entries from /var/log/audit/audit.log.
      Updating AppArmor profiles in /etc/apparmor.d.
      
      Profile:  /usr/sbin/xinetd
      Program:  xinetd
      Execute:  /usr/lib/cups/daemon/cups-lpd
      Severity: unknown
      
      [(I)nherit] / (P)rofile / (U)nconfined / (D)eny / Abo(r)t / (F)inish
      
      Inherit (ix)

      The child inherits the parent's profile, running with the same access controls as the parent. This mode is useful when a confined program needs to call another confined program without gaining the permissions of the target's profile or losing the permissions of the current profile. This mode is often used when the child program is a helper application, such as the /usr/bin/mail client using less as a pager or the Mozilla* Web browser using Adobe Acrobat* to display PDF files.

      Profile (px)

      The child runs using its own profile, which must be loaded into the kernel. If the profile is not present, attempts to execute the child fail with permission denied. This is most useful if the parent program is invoking a global service, such as DNS lookups or sending mail with your system's MTA.

      Choose the profile with clean exec (Px) option to scrub the environment of environment variables that could modify execution behavior when passed to the child process.

      Unconfined (ux)

      The child runs completely unconfined without any AppArmor profile applied to the executed resource.

      Choose the unconfined with clean exec (Ux) option to scrub the environment of environment variables that could modify execution behavior when passed to the child process. This option introduces a security vulnerability that could be used to exploit AppArmor. Only use it as a last resort.

      mmap (m)

      This permission denotes that the program running under the profile can access the resource using the mmap system call with the flag PROT_EXEC. This means that the data mapped in it can be executed. You are prompted to include this permission if it is requested during a profiling run.

      Deny

      Prevents the program from accessing the specified directory path entries. AppArmor then continues to the next event.

      Abort

      Aborts aa-logprof, losing all rule changes entered so far and leaving all profiles unmodified.

      Finish

      Closes aa-logprof, saving all rule changes entered so far and modifying all profiles.

    • Example 4-2 shows AppArmor suggesting directory path entries that have been accessed by the application being profiled. It might also require you to define execute permissions for entries.

      Example 4-2 Learning Mode Exception: Defining Execute Permissions for an Entry

      Adding /bin/ps ix to profile.
      
      Profile:  /usr/sbin/xinetd
      Path:     /etc/hosts.allow
      New Mode: r
      
       [1 - /etc/hosts.allow]
      
      [(A)llow] / (D)eny / (N)ew / (G)lob / Glob w/(E)xt / Abo(r)t / (F)inish
      

      AppArmor provides one or more paths or includes. By entering the option number, select the desired options then proceed to the next step.

      NOTE: All of these options are not always presented in the AppArmor menu.

      #include

      This is the section of an AppArmor profile that refers to an include file, which procures access permissions for programs. By using an include, you can give the program access to directory paths or files that are also required by other programs. Using includes can reduce the size of a profile. It is good practice to select includes when suggested.

      Globbed Version

      This is accessed by selecting Glob as described in the next step. For information about globbing syntax, refer to Section 2.1.2, Paths and Globbing.

      Actual Path

      This is the literal path to which the program needs access so that it can run properly.

      After you select the path or include, process it as an entry into the AppArmor profile by selecting Allow or Deny. If you are not satisfied with the directory path entry as it is displayed, you can also Glob it.

      The following options are available to process the learning mode entries and build the profile:

      Select Enter

      Allows access to the selected directory path.

      Allow

      Allows access to the specified directory path entries. AppArmor suggests file permission access. For more information, refer to Section 2.1.3, File Permission Access Modes.

      Deny

      Prevents the program from accessing the specified directory path entries. AppArmor then continues to the next event.

      New

      Prompts you to enter your own rule for this event, allowing you to specify a regular expression. If the expression does not actually satisfy the event that prompted the question in the first place, AppArmor asks for confirmation and lets you reenter the expression.

      Glob

      Select a specific path or create a general rule using wild cards that match a broader set of paths. To select any of the offered paths, enter the number that is printed in front of the path then decide how to proceed with the selected item.

      For more information about globbing syntax, refer to Section 2.1.2, Paths and Globbing.

      Glob w/Ext

      This modifies the original directory path while retaining the filename extension. For example, /etc/apache2/file.ext becomes /etc/apache2/*.ext, adding the wild card (asterisk) in place of the filename. This allows the program to access all files in the suggested directory that end with the .ext extension.

      Abort

      Aborts aa-logprof, losing all rule changes entered so far and leaving all profiles unmodified.

      Finish

      Closes aa-logprof, saving all rule changes entered so far and modifying all profiles.

  6. To view and edit your profile using vim, enter vim /etc/apparmor.d/profilename in a terminal window.

  7. Restart AppArmor and reload the profile set including the newly created one using the rcapparmor restart command.

Like the graphical front-end for building AppArmor profiles, the YaST Add Profile Wizard, aa-genprof also supports the use of the local profile repository under /etc/apparmor/profiles/extras and the remote AppArmor profile repository.

To use a profile from the local repository, proceed as follows:

  1. Start aa-genprof as described above.

    If aa-genprof finds an inactive local profile, the following lines appear on your terminal window:

    Profile: /usr/bin/opera
    
     [1 - Inactive local profile for /usr/bin/opera]
    
    [(V)iew Profile] / (U)se Profile / (C)reate New Profile / Abo(r)t / (F)inish
  2. If you want to just use this profile, hit U (Use Profile) and follow the profile generation procedure outlined above.

    If you want to examine the profile before activating it, hit V (View Profile).

    If you want to ignore the existing profile, hit C (Create New Profile) and follow the profile generation procedure outlined above to create the profile from scratch.

  3. Leave aa-genprof by hitting F (Finish) when you are done and save your changes.

To use the remote AppArmor profile repository with aa-genprof, proceed as follows:

  1. Start aa-genprof as described above.

    If aa-genprof detects a suitable profile on the repository server, the following lines appear on your terminal window:

    Repository: http://apparmor.opensuse.org/backend/api
    
    Would you like to enable access to the profile repository?
    
    (E)nable Repository / (D)isable Repository / Ask Me (L)ater
    
  2. Hit E (Enable Repository) to enable the repository.

  3. Determine whether you want to aa-genprof to upload any profiles to the repository server:

    Would you like to upload newly created and changed profiles to
          the profile repository?
    
    (Y)es / (N)o / Ask Me (L)ater
    

    Hit Y (Yes), if you want to enable profile upload or select N (No), if you want aa-genprof to just pull profiles from the repository, but not to upload any.

  4. Create a new user on the profile repository server to be able to upload profiles. Provide username and password.

  5. Determine whether you want to use the profile downloaded from the server or whether you would just like to review it:

    Profile: /usr/bin/opera
    
     [1 - novell]
    
    [(V)iew Profile] / (U)se Profile / (C)reate New Profile / Abo(r)t / (F)inish
    

    If you want to just use this profile, hit U (Use Profile) and follow the profile generation procedure outlined above.

    If you want to examine the profile before activating it, hit V (View Profile).

    If you want to ignore the existing profile, hit C (Create New Profile) and follow the profile generation procedure outlined above to create the profile from scratch.

  6. Leave aa-genprof by hitting F (Finish) when you are done and save the profile.

    If you opted for uploading your profile, provide a short change log and push it to the repository.

aa-logprof—Scanning the System Log

aa-logprof is an interactive tool used to review the learning or complain mode output found in the log entries in /var/log/audit/audit.log or /var/log/messages (if auditd is not running) and generate new entries in AppArmor security profiles.

When you run aa-logprof, it begins to scan the log files produced in learning or complain mode and, if there are new security events that are not covered by the existing profile set, it gives suggestions for modifying the profile. The learning or complain mode traces program behavior and enters it in the log. aa-logprof uses this information to observe program behavior.

If a confined program forks and executes another program, aa-logprof sees this and asks the user which execution mode should be used when launching the child process. The execution modes ix, px, Px, ux, and Ux are options for starting the child process. If a separate profile exists for the child process, the default selection is px. If one does not exist, the profile defaults to ix. Child processes with separate profiles have aa-autodep run on them and are loaded into AppArmor, if it is running.

When aa-logprof exits, profiles are updated with the changes. If the AppArmor module is running, the updated profiles are reloaded and, if any processes that generated security events are still running in the null-complain-profile, those processes are set to run under their proper profiles.

HINT: Support for the External Profile Repository

Similar to the aa-genprof, aa-logprof also supports profile exchange with the external repository server. For background information on the use of the external AppArmor profile repository, refer to Section 2.5, Using the External AppArmor Profile Repository. For details on how to configure access and access mode to the server, check the procedure described under aa-genprof—Generating Profiles.

To run aa-logprof, enter aa-logprof into a terminal window while logged in as root. The following options can be used for aa-logprof:

aa-logprof -d /path/to/profile/directory/

Specifies the full path to the location of the profiles if the profiles are not located in the standard directory, /etc/apparmor.d/.

aa-logprof -f /path/to/logfile/

Specifies the full path to the location of the log file if the log file is not located in the default directory, /var/log/audit/audit.log or /var/log/messages (if auditd is not running).

aa-logprof -m "string marker in logfile"

Marks the starting point for aa-logprof to look in the system log. aa-logprof ignores all events in the system log before the specified mark. If the mark contains spaces, it must be surrounded by quotes to work correctly. For example:

aa-logprof -m"17:04:21"

or

logprof -m e2ff78636296f16d0b5301209a04430d

aa-logprof scans the log, asking you how to handle each logged event. Each question presents a numbered list of AppArmor rules that can be added by pressing the number of the item on the list.

By default, aa-logprof looks for profiles in /etc/apparmor.d/ and scans the log in /var/log/messages. In many cases, running aa-logprof as root is enough to create the profile.

However, there might be times when you need to search archived log files, such as if the program exercise period exceeds the log rotation window (when the log file is archived and a new log file is started). If this is the case, you can enter zcat -f `ls -1tr /var/log/messages*` | aa-logprof -f -.

aa-logprof Example 1

The following is an example of how aa-logprof addresses httpd2-prefork accessing the file /etc/group. [] indicates the default option.

In this example, the access to /etc/group is part of httpd2-prefork accessing name services. The appropriate response is 1, which includes a predefined set of AppArmor rules. Selecting 1 to #include the name service package resolves all of the future questions pertaining to DNS lookups and also makes the profile less brittle in that any changes to DNS configuration and the associated name service profile package can be made just once, rather than needing to revise many profiles.

Profile:  /usr/sbin/httpd2-prefork
Path:     /etc/group
New Mode: r

[1 - #include <abstractions/nameservice>]
 2 - /etc/group
[(A)llow] / (D)eny / (N)ew / (G)lob / Glob w/(E)xt / Abo(r)t / (F)inish

Select one of the following responses:

Select Enter

Triggers the default action, which is, in this example, allowing access to the specified directory path entry.

Allow

Allows access to the specified directory path entries. AppArmor suggests file permission access. For more information about this, refer to Section 2.1.3, File Permission Access Modes.

Deny

Prevents the program from accessing the specified directory path entries. AppArmor then continues to the next event.

New

Prompts you to enter your own rule for this event, allowing you to specify whatever form of regular expression you want. If the expression entered does not actually satisfy the event that prompted the question in the first place, AppArmor asks for confirmation and lets you reenter the expression.

Glob

Select either a specific path or create a general rule using wild cards that matches on a broader set of paths. To select any of the offered paths, enter the number that is printed in front of the paths then decide how to proceed with the selected item.

For more information about globbing syntax, refer to Section 2.1.2, Paths and Globbing.

Glob w/Ext

This modifies the original directory path while retaining the filename extension. For example, /etc/apache2/file.ext becomes /etc/apache2/*.ext, adding the wild card (asterisk) in place of the filename. This allows the program to access all files in the suggested directory that end with the .ext extension.

Abort

Aborts aa-logprof, losing all rule changes entered so far and leaving all profiles unmodified.

Finish

Closes aa-logprof, saving all rule changes entered so far and modifying all profiles.

aa-logprof Example 2

For example, when profiling vsftpd, see this question:

Profile:  /usr/sbin/vsftpd
Path:     /y2k.jpg
New Mode: r

[1 - /y2k.jpg]

(A)llow / [(D)eny] / (N)ew / (G)lob / Glob w/(E)xt / Abo(r)t / (F)inish

Several items of interest appear in this question. First, note that vsftpd is asking for a path entry at the top of the tree, even though vsftpd on openSUSE serves FTP files from /srv/ftp by default. This is because httpd2-prefork uses chroot and, for the portion of the code inside the chroot jail, AppArmor sees file accesses in terms of the chroot environment rather than the global absolute path.

The second item of interest is that you might want to grant FTP read access to all JPEG files in the directory, so you could use Glob w/Ext and use the suggested path of /*.jpg. Doing so collapses all previous rules granting access to individual .jpg files and forestalls any future questions pertaining to access to .jpg files.

Finally, you might want to grant more general access to FTP files. If you select Glob in the last entry, aa-logprof replaces the suggested path of /y2k.jpg with /*. Alternatively, you might want to grant even more access to the entire directory tree, in which case you could use the New path option and enter /**.jpg (which would grant access to all .jpg files in the entire directory tree) or /** (which would grant access to all files in the directory tree).

These items deal with read accesses. Write accesses are similar, except that it is good policy to be more conservative in your use of regular expressions for write accesses. Dealing with execute accesses is more complex. Find an example in Example 4-1.

In the following example, the /usr/bin/mail mail client is being profiled and aa-logprof has discovered that /usr/bin/mail executes /usr/bin/less as a helper application to page long mail messages. Consequently, it presents this prompt:

/usr/bin/nail -> /usr/bin/less
(I)nherit / (P)rofile / (U)nconfined / (D)eny

HINT: The actual executable file for /usr/bin/mail turns out to be /usr/bin/nail, which is not a typographical error.

The program /usr/bin/less appears to be a simple one for scrolling through text that is more than one screen long and that is in fact what /usr/bin/mail is using it for. However, less is actually a large and powerful program that makes use of many other helper applications, such as tar and rpm.

HINT: Run less on a tar file or an RPM file and it shows you the inventory of these containers.

You do not want to run rpm automatically when reading mail messages (that leads directly to a Microsoft* Outlook–style virus attack, because rpm has the power to install and modify system programs), so, in this case, the best choice is to use Inherit. This results in the less program executed from this context running under the profile for /usr/bin/mail. This has two consequences:

  • You need to add all of the basic file accesses for /usr/bin/less to the profile for /usr/bin/mail.

  • You can avoid adding the helper applications, such as tar and rpm, to the /usr/bin/mail profile so that when /usr/bin/mail runs /usr/bin/less in this context, the less program is far less dangerous than it would be without AppArmor protection.

In other circumstances, you might instead want to use the Profile option. This has two effects on aa-logprof:

  • The rule written into the profile uses px, which forces the transition to the child's own profile.

  • aa-logprof constructs a profile for the child and starts building it, in the same way that it built the parent profile, by assigning events for the child process to the child's profile and asking the aa-logprof user questions.

If a confined program forks and executes another program, aa-logprof sees this and asks the user which execution mode should be used when launching the child process. The execution modes of inherit, profile, unconfined or an option to deny the execution are presented.

If a separate profile exists for the child process, the default selection is profile. If a profile does not exist, the default is inherit. The inherit option, or ix, is described in Section 2.1.3, File Permission Access Modes.

The profile option indicates that the child program should run in its own profile—a secondary question asks whether to sanitize the environment that the child program inherits from the parent. If you choose to sanitize the environment, this places the execution modifier Px in your AppArmor profile. If you select not to sanitize, px is placed in the profile and no environment sanitizing occurs. The default for the execution mode is px if you select profile execution mode.

The unconfined execution mode is not recommended and should only be used in cases where there is no other option to generate a profile for a program reliably. Selecting unconfined opens a warning dialog asking for confirmation of the choice. If you are sure and choose Yes, a second dialog ask whether to sanitize the environment. Choosing Yes uses the execution mode Ux in your profile. Choosing No uses the execution mode ux for your profile. The default value selected is Ux for unconfined execution mode.

IMPORTANT: Running Unconfined

Choosing ux is very dangerous and provides no enforcement of policy from a security perspective of resulting execution behavior of the child program.

aa-unconfined—Identifying Unprotected Processes

The aa-unconfined command examines open network ports on your system, compares that to the set of profiles loaded on your system, and reports network services that do not have AppArmor profiles. It requires root privileges and that it not be confined by an AppArmor profile.

aa-unconfined must be run as root to retrieve the process executable link from the /proc file system. This program is susceptible to the following race conditions:

  • An unlinked executable is mishandled

  • A process that dies between netstat(8) and further checks is mishandled

NOTE: This program lists processes using TCP and UDP only. In short, this program is unsuitable for forensics use and is provided only as an aid to profiling all network-accessible processes in the lab.

AppArmor Admin Guide
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