selinux: fix double free in selinux_parse_opts_str()

commit 023f108dcc187e34ef864bf10ed966cf25e14e2a upstream.

This patch is based on a discussion generated by an earlier patch
from Tetsuo Handa:

* https://marc.info/?t=149035659300001&r=1&w=2

The double free problem involves the mnt_opts field of the
security_mnt_opts struct, selinux_parse_opts_str() frees the memory
on error, but doesn't set the field to NULL so if the caller later
attempts to call security_free_mnt_opts() we trigger the problem.

In order to play it safe we change selinux_parse_opts_str() to call
security_free_mnt_opts() on error instead of free'ing the memory
directly.  This should ensure that everything is handled correctly,
regardless of what the caller may do.

Fixes: e000752989 ("LSM/SELinux: Interfaces to allow FS to control mount options")
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Paul Moore 2017-06-07 16:48:19 -04:00 committed by syphyr
parent 5b2ec0a38d
commit cb4e7ced75
1 changed files with 2 additions and 3 deletions

View File

@ -971,10 +971,8 @@ static int selinux_parse_opts_str(char *options,
goto out_err;
opts->mnt_opts_flags = kcalloc(NUM_SEL_MNT_OPTS, sizeof(int), GFP_ATOMIC);
if (!opts->mnt_opts_flags) {
kfree(opts->mnt_opts);
if (!opts->mnt_opts_flags)
goto out_err;
}
if (fscontext) {
opts->mnt_opts[num_mnt_opts] = fscontext;
@ -997,6 +995,7 @@ static int selinux_parse_opts_str(char *options,
return 0;
out_err:
security_free_mnt_opts(opts);
kfree(context);
kfree(defcontext);
kfree(fscontext);