Messages in this thread | | | Date | Fri, 22 May 2015 07:51:19 -0700 | From | Mark Salyzyn <> | Subject | Re: net/unix: sk_socket can disappear when state is unlocked |
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On 05/22/2015 02:50 AM, Hannes Frederic Sowa wrote: > On Do, 2015-05-21 at 09:25 -0700, Mark Salyzyn wrote: >> got a rare NULL pointer dereference in clear_bit >> >> Signed-off-by: Mark Salyzyn <salyzyn@android.com> >> --- >> net/unix/af_unix.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c >> index 5266ea7..37a8925 100644 >> --- a/net/unix/af_unix.c >> +++ b/net/unix/af_unix.c >> @@ -1880,6 +1880,11 @@ static long unix_stream_data_wait(struct sock *sk, long timeo, >> unix_state_unlock(sk); >> timeo = freezable_schedule_timeout(timeo); >> unix_state_lock(sk); >> + >> + /* sk_socket may have been killed while unlocked */ >> + if (!sk->sk_socket) >> + break; >> + >> clear_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags); >> } >> > Canonical way is to test for sock_flag(sk, SOCK_DEAD). Also it does not > seem like we are returning an error to user space but are still looping > to try to dequeue skbs from sk_receive_queue, which is concurrently > emptied by unix_release (maybe, without holding unix_state_lock). > > Bye, > Hannes > I will send an updated patch shortly.
It may be acceptable given the expectation that sk_set_socket(sk, NULL) occurs after SOCK_DEAD flag is set since we would not be here during the socket initialization/connection phases. As such, for all phases (and I re-iterate, we can only be here if in connected state), it is not a generic guarantee of sk_socket != NULL. But I only saw one apparent example (in net/decnet/dn_nsp_in.c) of using sock_flag(sk, SOCK_DEAD) as protection against a possible deference NULL access with sk_socket, and many KISS examples of checking sk_socket for NULL to protect against thus.
Thanks for making me look though, it appears that I missed the same problem in net/caif/caif_socket.c and will add it!
Sincerely -- Mark Salyzyn
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