[PATCH] tun: fix mismatch in mutex lock-unlock in tun_get_user()

[Alexey Khoroshilov]

There is a single error path where tfile->napi_mutex is left unlocked.
It can lead to a deadlock.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@xxxxxxxxx>
---
 drivers/net/tun.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 81e6cc951e7f..0072a9832532 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1879,6 +1879,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 			default:
 				this_cpu_inc(tun->pcpu_stats->rx_dropped);
 				kfree_skb(skb);
+				if (frags) {
+					tfile->napi.skb = NULL;
+					mutex_unlock(&tfile->napi_mutex);
+				}
 				return -EINVAL;
 			}
 		}
-- 
2.7.4