On Mon, 2024-05-20 at 18:41 -0300, Thadeu Lima de Souza Cascardo wrote: > sk_psock_get will return NULL if the refcount of psock has gone to 0, which > will happen when the last call of sk_psock_put is done. However, > sk_psock_drop may not have finished yet, so the close callback will still > point to sock_map_close despite psock being NULL. > > This can be reproduced with a thread deleting an element from the sock map, > while the second one creates a socket, adds it to the map and closes it. > > That will trigger the WARN_ON_ONCE: > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 7220 at net/core/sock_map.c:1701 sock_map_close+0x2a2/0x2d0 net/core/sock_map.c:1701 > Modules linked in: > CPU: 1 PID: 7220 Comm: syz-executor380 Not tainted 6.9.0-syzkaller-07726-g3c999d1ae3c7 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024 > RIP: 0010:sock_map_close+0x2a2/0x2d0 net/core/sock_map.c:1701 > Code: df e8 92 29 88 f8 48 8b 1b 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 79 29 88 f8 4c 8b 23 eb 89 e8 4f 15 23 f8 90 <0f> 0b 90 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d e9 13 26 3d 02 > RSP: 0018:ffffc9000441fda8 EFLAGS: 00010293 > RAX: ffffffff89731ae1 RBX: ffffffff94b87540 RCX: ffff888029470000 > RDX: 0000000000000000 RSI: ffffffff8bcab5c0 RDI: ffffffff8c1faba0 > RBP: 0000000000000000 R08: ffffffff92f9b61f R09: 1ffffffff25f36c3 > R10: dffffc0000000000 R11: fffffbfff25f36c4 R12: ffffffff89731840 > R13: ffff88804b587000 R14: ffff88804b587000 R15: ffffffff89731870 > FS: 000055555e080380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000000 CR3: 00000000207d4000 CR4: 0000000000350ef0 > Call Trace: > <TASK> > unix_release+0x87/0xc0 net/unix/af_unix.c:1048 > __sock_release net/socket.c:659 [inline] > sock_close+0xbe/0x240 net/socket.c:1421 > __fput+0x42b/0x8a0 fs/file_table.c:422 > __do_sys_close fs/open.c:1556 [inline] > __se_sys_close fs/open.c:1541 [inline] > __x64_sys_close+0x7f/0x110 fs/open.c:1541 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7fb37d618070 > Code: 00 00 48 c7 c2 b8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff eb d4 e8 10 2c 00 00 80 3d 31 f0 07 00 00 74 17 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c > RSP: 002b:00007ffcd4a525d8 EFLAGS: 00000202 ORIG_RAX: 0000000000000003 > RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fb37d618070 > RDX: 0000000000000010 RSI: 00000000200001c0 RDI: 0000000000000004 > RBP: 0000000000000000 R08: 0000000100000000 R09: 0000000100000000 > R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > </TASK> > > Use sk_psock, which will only check that the pointer is not been set to > NULL yet, which should only happen after the callbacks are restored. If, > then, a reference can still be gotten, we may call sk_psock_stop and cancel > psock->work. > > After that change, the reproducer does not trigger the WARN_ON_ONCE > anymore. > > Reported-by: syzbot+07a2e4a1a57118ef7355@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=07a2e4a1a57118ef7355 > Fixes: aadb2bb83ff7 ("sock_map: Fix a potential use-after-free in sock_map_close()") > Fixes: 5b4a79ba65a1 ("bpf, sockmap: Don't let sock_map_{close,destroy,unhash} call itself") > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxx> > --- > net/core/sock_map.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index 9402889840bf..13267e667a4c 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -1680,19 +1680,23 @@ void sock_map_close(struct sock *sk, long timeout) > > lock_sock(sk); > rcu_read_lock(); > - psock = sk_psock_get(sk); > + psock = sk_psock(sk); > if (unlikely(!psock)) { > + saved_close = READ_ONCE(sk->sk_prot)->close; > rcu_read_unlock(); > release_sock(sk); > - saved_close = READ_ONCE(sk->sk_prot)->close; > } else { > saved_close = psock->saved_close; > sock_map_remove_links(sk, psock); > + psock = sk_psock_get(sk); > rcu_read_unlock(); > - sk_psock_stop(psock); > + if (psock) > + sk_psock_stop(psock); > release_sock(sk); > - cancel_delayed_work_sync(&psock->work); > - sk_psock_put(sk, psock); > + if (psock) { > + cancel_delayed_work_sync(&psock->work); > + sk_psock_put(sk, psock); > + } > } > > /* Make sure we do not recurse. This is a bug. As a personal opinion I think the code will become simple reordering the condition, something alike: if (psock) { saved_close = psock->saved_close; sock_map_remove_links(sk, psock); psock = sk_psock_get(sk); if (!psock) goto no_psock; rcu_read_unlock(); sk_psock_stop(psock); release_sock(sk); cancel_delayed_work_sync(&psock->work); sk_psock_put(sk, psock); } else { no_psock: saved_close = READ_ONCE(sk->sk_prot)->close; rcu_read_unlock(); release_sock(sk); } Overall looks safe to me, but I would appreciate an explicit ack from Jakub S. or John. Cheers, Paolo
