[PATCH Oneiric SRU] UBUNTU SAUCE: apparmor: fix IRQ stack overflow

Tim Gardner tim.gardner at canonical.com
Wed Sep 26 16:11:10 UTC 2012


From: John Johansen <john.johansen at canonical.com>

BugLink: http://bugs.launchpad.net/bugs/1056078

Profile replacement can cause a long chain of profiles to build up
that get freed in a cascading chain of free_profile calls. Because
free_profile is being called via aa_put_profile (and hence kref_put)
each profile free is done via what amounts to recursion. That is
free_profile indirectly calls free_profile on the next profile in the
chain via aa_put_profile.

Break this recursion by directly walking the chain, and as long as
a profile is being freed because it has no more references continue
on to the next profile. This results in at most 2 levels of free_profile
being called.

Signed-off-by: John Johansen <john.johansen at canonical.com>
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 security/apparmor/policy.c |   24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index 4d5ce13..b5c5b8b 100644
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -724,6 +724,8 @@ fail:
  */
 static void free_profile(struct aa_profile *profile)
 {
+	struct aa_profile *p;
+
 	AA_DEBUG("%s(%p)\n", __func__, profile);
 
 	if (!profile)
@@ -751,7 +753,27 @@ static void free_profile(struct aa_profile *profile)
 	aa_free_sid(profile->sid);
 	aa_put_dfa(profile->xmatch);
 
-	aa_put_profile(profile->replacedby);
+	/* put the profile reference, but not via put_profile/kref_put
+	 * replacedby can form a long chain that can result in cascading
+	 * frees that blows the stack lp#1056078. The long chain creation
+	 * should be addressed in profile replacement.
+	 * This just addresses recursion of free_profile causing the
+	 * stack to blow.
+	 */
+	for (p = profile->replacedby; p; ) {
+		if (atomic_dec_and_test(&p->base.count.refcount)) {
+			/* no more refs on p, grab its replacedby */
+			struct aa_profile *next = p->replacedby;
+			/* break the chain */
+			p->replacedby = NULL;
+			/* now free p, chain is broken */
+			free_profile(p);
+
+			/* follow up with next profile in the chain */
+			p = next;
+		} else
+			break;
+	}
 
 	kzfree(profile);
 }
-- 
1.7.9.5





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