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Fix SELinux labels in cgroup filesystem root directory (#7496)

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When using SELinux with legacy cgroups the tmpfs on /sys/fs/cgroup is by
default labelled as tmpfs_t. This label is also inherited by the "cpu"
and "cpuacct" symbolic links. Unfortunately the policy expects them to
be labelled as cgroup_t, which is used for all the actual cgroup
filesystems. Failure to do so results in a stream of denials.

This state cannot be fixed reliably when the cgroup filesystem structure
is set-up as the SELinux policy is not yet loaded at this
moment. It also cannot be fixed later as the root of the cgroup
filesystem is remounted read-only. In order to fix it the root of the
cgroup filesystem needs to be temporary remounted read-write, relabelled
and remounted back read-only.
This commit is contained in:
Krzysztof Nowicki 2017-11-30 11:59:29 +01:00 committed by Lennart Poettering
parent 949befd3f0
commit 8739f23e3c
1 changed files with 11 additions and 1 deletions
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12
src/core/mount-setup.c
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@ -390,9 +390,19 @@ int mount_setup(bool loaded_policy) {
nftw("/dev/shm", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
nftw("/run", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
/* Temporarily remount the root cgroup filesystem to give it a proper label. */
r = cg_all_unified();
if (r == 0) {
(void) mount(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT, NULL);
label_fix("/sys/fs/cgroup", false, false);
nftw("/sys/fs/cgroup", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
(void) mount(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT|MS_RDONLY, NULL);
} else if (r < 0)
return log_error_errno(r, "Failed to determine whether we are in all unified mode: %m");
after_relabel = now(CLOCK_MONOTONIC);
log_info("Relabelled /dev and /run in %s.",
log_info("Relabelled /dev, /run and /sys/fs/cgroup in %s.",
format_timespan(timespan, sizeof(timespan), after_relabel - before_relabel, 0));
}
#endif