device_cgroup: fix RCU imbalance in error case

When dev_exception_add() returns an error (due to a failed memory
allocation), make sure that we move the RCU preemption count back to where
it was before we were called. We dropped the RCU read lock inside the loop
body, so we can't just "break".

sparse complains about this, too:

$ make -s C=2 security/device_cgroup.o
./include/linux/rcupdate.h:647:9: warning: context imbalance in
'propagate_exception' - unexpected unlock

Fixes: d591fb56618f ("device_cgroup: simplify cgroup tree walk in propagate_exception()")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index cd97929fac663f61250edeae3397e3ab75b5ff49..dc28914fa72e076405b238225dc54c172df5de40 100644 (file)
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -560,7 +560,7 @@ static int propagate_exception(struct dev_cgroup *devcg_root,
                    devcg->behavior == DEVCG_DEFAULT_ALLOW) {
                        rc = dev_exception_add(devcg, ex);
                        if (rc)
-                               break;
+                               return rc;
                } else {
                        /*
                         * in the other possible cases: