linux-kernel - [PATCH 4.4 166/168] device_cgroup: fix RCU imbalance in error case

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Date:   Wed, 24 Apr 2019 19:10:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Michal Hocko <mhocko@...e.com>, Tejun Heo <tj@...nel.org>
Subject: [PATCH 4.4 166/168] device_cgroup: fix RCU imbalance in error case

From: Jann Horn <jannh@...gle.com>

commit 0fcc4c8c044e117ac126ab6df4138ea9a67fa2a9 upstream.

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@...r.kernel.org
Signed-off-by: Jann Horn <jannh@...gle.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 security/device_cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -568,7 +568,7 @@ static int propagate_exception(struct de
 		    devcg->behavior == DEVCG_DEFAULT_ALLOW) {
 			rc = dev_exception_add(devcg, ex);
 			if (rc)
-				break;
+				return rc;
 		} else {
 			/*
 			 * in the other possible cases: