apparmor: fix refcount race when finding a child profile

When finding a child profile via an rcu critical section, the profile
may be put and scheduled for deletion after the child is found but
before its refcount is incremented.

Protect against this by repeating the lookup if the profiles refcount
is 0 and is one its way to deletion.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index ca402d028db8b06a0306e79341e249294ffe1ab2..780712553651d04e9888bad6830441445167e1f3 100644 (file)
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -766,7 +766,9 @@ struct aa_profile *aa_find_child(struct aa_profile *parent, const char *name)
        struct aa_profile *profile;
 
        rcu_read_lock();
-       profile = aa_get_profile(__find_child(&parent->base.profiles, name));
+       do {
+               profile = __find_child(&parent->base.profiles, name);
+       } while (profile && !aa_get_profile_not0(profile));
        rcu_read_unlock();
 
        /* refcount released by caller */