AA_CHANGE_PROFILE(2) AppArmor AA_CHANGE_PROFILE(2)NAME
aa_change_profile, aa_change_onexec - change a tasks profile
SYNOPSIS
#include <sys/apparmor.h>
int aa_change_profile(const char *profile);
int aa_change_onexec(const char *profile);
Link with -lapparmor when compiling.
DESCRIPTION
An AppArmor profile applies to an executable program; if a portion of
the program needs different access permissions than other portions, the
program can "change profile" to a different profile. To change into a
new profile, it can use the aa_change_profile() function to do so. It
passes in a pointer to the profile to transition to. Transitioning to
another profile via aa_change_profile() is permanent and the process is
not permitted to transition back to the original profile. Confined
programs wanting to use aa_change_profile() need to have rules
permitting changing to the named profile. See apparmor.d(8) for
details.
If a program wants to return out of the current profile to the original
profile, it should use aa_change_hat(2) instead.
Open file descriptors are not remediated after a call to
aa_change_profile() so the calling program must close(2) open file
descriptors to ensure they are not available after calling
aa_change_profile(). As aa_change_profile() is typically used just
before execve(2), you may want to use open(2) or fcntl(2) with close-
on-exec.
The aa_change_onexec() function is like the aa_change_profile()
function except it specifies that the profile transition should take
place on the next exec instead of immediately. The delayed profile
change takes precedence over any exec transition rules within the
confining profile. Delaying the profile boundary has a couple of
advantages, it removes the need for stub transition profiles and the
exec boundary is a natural security layer where potentially sensitive
memory is unmapped.
RETURN VALUE
On success zero is returned. On error, -1 is returned, and errno(3) is
set appropriately.
ERRORS
EINVAL
The apparmor kernel module is not loaded, neither a profile nor a
namespace was specified, or the communication via the
/proc/*/attr/current file did not conform to protocol.
ENOMEM
Insufficient kernel memory was available.
EPERM
The calling application is not confined by apparmor, or the
no_new_privs bit is set.
EACCES
The task does not have sufficient permissions to change its domain.
ENOENT
The specified profile does not exist, or is not visible from the
current Namespace.
EXAMPLE
The following example shows a simple, if contrived, use of
aa_change_profile(); a typical use of aa_change_profile() will
aa_change_profile() just before an execve(2) so that the new child
process is permanently confined.
#include <stdlib.h>
#include <string.h>
#include <sys/apparmor.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main(int argc, char * argv[])
{
int fd;
char buf[10];
char *execve_args[4];
printf("Before aa_change_profile():\n");
if ((fd=open("/etc/passwd", O_RDONLY)) < 0) {
perror("Failure opening /etc/passwd");
return 1;
}
/* Confirm for ourselves that we can really read /etc/passwd */
memset(&buf, 0, 10);
if (read(fd, &buf, 10) == -1) {
perror("Failure reading /etc/passwd");
return 1;
}
buf[9] = '\0';
printf("/etc/passwd: %s\n", buf);
close(fd);
printf("After aa_change_profile():\n");
/* change profile to the "i_cant_be_trusted_anymore" profile, which
* should not have read access to /etc/passwd. */
if (aa_change_profile("i_cant_be_trusted_anymore") < 0) {
perror("Failure changing profile -- aborting");
_exit(1);
}
/* confirm that we cannot read /etc/passwd */
execve_args[0] = "/usr/bin/head";
execve_args[1] = "-1";
execve_args[2] = "/etc/passwd";
execve_args[3] = NULL;
execve("/usr/bin/head", execve_args, NULL);
perror("execve");
_exit(1);
}
This code example requires a profile similar to the following to be
loaded with apparmor_parser(8):
profile i_cant_be_trusted_anymore {
/etc/ld.so.cache mr,
/lib/ld-*.so* mrix,
/lib/libc*.so* mr,
/usr/bin/head ix,
}
The output when run:
$ /tmp/change_p
Before aa_change_profile():
/etc/passwd: root:x:0:
After aa_change_profile():
/usr/bin/head: cannot open `/etc/passwd' for reading: Permission denied
$
If /tmp/change_p is to be confined as well, then the following profile
can be used (in addition to the one for 'i_cant_be_trusted_anymore',
above):
# Confine change_p to be able to read /etc/passwd and aa_change_profile()
# to the 'i_cant_be_trusted_anymore' profile.
/tmp/change_p {
/etc/ld.so.cache mr,
/lib/ld-*.so* mrix,
/lib/libc*.so* mr,
/etc/passwd r,
# Needed for aa_change_profile()
/usr/lib/libapparmor*.so* mr,
/proc/[0-9]*/attr/current w,
change_profile -> i_cant_be_trusted_anymore,
}
BUGS
None known. If you find any, please report them at
<https://bugs.launchpad.net/apparmor/+filebug>. Note that using
aa_change_profile(2) without execve(2) provides no memory barriers
between different areas of a program; if address space separation is
required, then separate processes should be used.
SEE ALSOapparmor(7), apparmor.d(5), apparmor_parser(8), aa_change_hat(2) and
<http://wiki.apparmor.net>.
AppArmor 2.8.2 2013-10-21 AA_CHANGE_PROFILE(2)
