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tun: add mutex_unlock() call and napi.skb clearing in tun_get_user()

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If both IFF_NAPI_FRAGS mode and XDP are enabled, and the XDP program
consumes the skb, we need to clear the napi.skb (or risk
a use-after-free) and release the mutex (or risk a deadlock)

WARNING: lock held when returning to user space!
5.5.0-rc6-syzkaller #0 Not tainted
------------------------------------------------
syz-executor.0/455 is leaving the kernel with locks still held!
1 lock held by syz-executor.0/455:
 #0: ffff888098f6e748 (&tfile->napi_mutex){+.+.}, at: tun_get_user+0x1604/0x3fc0 drivers/net/tun.c:1835

Fixes: 90e33d4594 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Petar Penkov <ppenkov@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2020-01-22 09:07:35 -08:00 committed by David S. Miller
parent 971de2e572
commit 1efba987c4
1 changed files with 4 additions and 0 deletions
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4
drivers/net/tun.c
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@ -1936,6 +1936,10 @@ drop:
if (ret != XDP_PASS) {
rcu_read_unlock();
local_bh_enable();
if (frags) {
tfile->napi.skb = NULL;
mutex_unlock(&tfile->napi_mutex);
}
return total_len;
}
}