[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 <khoroshi...@ispras.ru>
---
 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