apparmor: fix IRQ stack overflow during free_profile (2e680dd6) · Commits · 戴 / test

BugLink: http://bugs.launchpad.net/bugs/1056078 Profile replacement can cause long chains of profiles to build up when the profile being replaced is pinned. When the pinned profile is finally freed, it puts the reference to its replacement, which may in turn nest another call to free_profile on the stack. Because this may happen for each profile in the replacedby chain this can result in a recusion that causes the stack to overflow. Break this nesting by directly walking the chain of replacedby profiles (ie. use iteration instead of recursion to free the list). This results in at most 2 levels of free_profile being called, while freeing a replacedby chain. Signed-off-by:

John Johansen <john.johansen@canonical.com> Signed-off-by:

James Morris <james.l.morris@oracle.com>

security/apparmor/policy.c

+23 −1

Original line number	Diff line number	Diff line
		@@ -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_put_dfa(profile->xmatch);
		aa_put_dfa(profile->policy.dfa);

		aa_put_profile(profile->replacedby);
		/* put the profile reference for replacedby, but not via
		* put_profile(kref_put).
		* replacedby can form a long chain that can result in cascading
		* frees that blows the stack because kref_put makes a nested fn
		* call (it looks like recursion, with free_profile calling
		* free_profile) for each profile in the chain lp#1056078.
		*/
		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);
		}

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