5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Gavrilov Ilia Ilia.Gavrilov@infotecs.ru
[ Upstream commit 0b9130247f3b6a1122478471ff0e014ea96bb735 ]
syzbot reported a memory leak in nr_create() [0].
Commit 409db27e3a2e ("netrom: Fix use-after-free of a listening socket.") added sock_hold() to the nr_heartbeat_expiry() function, where a) a socket has a SOCK_DESTROY flag or b) a listening socket has a SOCK_DEAD flag.
But in the case "a," when the SOCK_DESTROY flag is set, the file descriptor has already been closed and the nr_release() function has been called. So it makes no sense to hold the reference count because no one will call another nr_destroy_socket() and put it as in the case "b."
nr_connect nr_establish_data_link nr_start_heartbeat
nr_release switch (nr->state) case NR_STATE_3 nr->state = NR_STATE_2 sock_set_flag(sk, SOCK_DESTROY);
nr_rx_frame nr_process_rx_frame switch (nr->state) case NR_STATE_2 nr_state2_machine() nr_disconnect() nr_sk(sk)->state = NR_STATE_0 sock_set_flag(sk, SOCK_DEAD)
nr_heartbeat_expiry switch (nr->state) case NR_STATE_0 if (sock_flag(sk, SOCK_DESTROY) || (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) sock_hold() // ( !!! ) nr_destroy_socket()
To fix the memory leak, let's call sock_hold() only for a listening socket.
Found by InfoTeCS on behalf of Linux Verification Center (linuxtesting.org) with Syzkaller.
[0]: https://syzkaller.appspot.com/bug?extid=d327a1f3b12e1e206c16
Reported-by: syzbot+d327a1f3b12e1e206c16@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d327a1f3b12e1e206c16 Fixes: 409db27e3a2e ("netrom: Fix use-after-free of a listening socket.") Signed-off-by: Gavrilov Ilia Ilia.Gavrilov@infotecs.ru Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/netrom/nr_timer.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/netrom/nr_timer.c b/net/netrom/nr_timer.c index 4e7c968cde2dc..5e3ca068f04e0 100644 --- a/net/netrom/nr_timer.c +++ b/net/netrom/nr_timer.c @@ -121,7 +121,8 @@ static void nr_heartbeat_expiry(struct timer_list *t) is accepted() it isn't 'dead' so doesn't get removed. */ if (sock_flag(sk, SOCK_DESTROY) || (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) { - sock_hold(sk); + if (sk->sk_state == TCP_LISTEN) + sock_hold(sk); bh_unlock_sock(sk); nr_destroy_socket(sk); goto out;