From: Eric Dumazet <edumazet@google.com> [ Upstream commit 1efba987c48629c0c64703bb4ea76ca1a3771d17 ] 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: 90e33d459407 ("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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> --- drivers/net/tun.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 9ae854c..5589d6cd 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1899,6 +1899,10 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, if (ret != XDP_PASS) { rcu_read_unlock(); local_bh_enable(); + if (frags) { + tfile->napi.skb = NULL; + mutex_unlock(&tfile->napi_mutex); + } return total_len; } } -- 1.8.3