Messages in this thread | | | Date | Wed, 8 May 2024 12:26:37 -0700 | From | Breno Leitao <> | Subject | Re: [PATCH net-next] af_unix: Fix data races in unix_release_sock/unix_stream_sendmsg |
| |
On Wed, May 08, 2024 at 10:33:24AM -0700, Kuniyuki Iwashima wrote: > From: Breno Leitao <leitao@debian.org> > Date: Wed, 8 May 2024 04:17:45 -0700 > > A data-race condition has been identified in af_unix. In one data path, > > the write function unix_release_sock() atomically writes to > > sk->sk_shutdown using WRITE_ONCE. However, on the reader side, > > unix_stream_sendmsg() does not read it atomically. Consequently, this > > issue is causing the following KCSAN splat to occur: > > > > BUG: KCSAN: data-race in unix_release_sock / unix_stream_sendmsg > > > > write (marked) to 0xffff88867256ddbb of 1 bytes by task 7270 on cpu 28: > > unix_release_sock (net/unix/af_unix.c:640) > > unix_release (net/unix/af_unix.c:1050) > > sock_close (net/socket.c:659 net/socket.c:1421) > > __fput (fs/file_table.c:422) > > __fput_sync (fs/file_table.c:508) > > __se_sys_close (fs/open.c:1559 fs/open.c:1541) > > __x64_sys_close (fs/open.c:1541) > > x64_sys_call (arch/x86/entry/syscall_64.c:33) > > do_syscall_64 (arch/x86/entry/common.c:?) > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) > > > > read to 0xffff88867256ddbb of 1 bytes by task 989 on cpu 14: > > unix_stream_sendmsg (net/unix/af_unix.c:2273) > > __sock_sendmsg (net/socket.c:730 net/socket.c:745) > > ____sys_sendmsg (net/socket.c:2584) > > __sys_sendmmsg (net/socket.c:2638 net/socket.c:2724) > > __x64_sys_sendmmsg (net/socket.c:2753 net/socket.c:2750 net/socket.c:2750) > > x64_sys_call (arch/x86/entry/syscall_64.c:33) > > do_syscall_64 (arch/x86/entry/common.c:?) > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) > > > > value changed: 0x01 -> 0x03 > > > > The line numbers are related to commit dd5a440a31fa ("Linux 6.9-rc7"). > > > > Commit e1d09c2c2f57 ("af_unix: Fix data races around sk->sk_shutdown.") > > addressed a comparable issue in the past regarding sk->sk_shutdown. > > However, it overlooked resolving this particular data path. > > > > To prevent potential race conditions in the future, all read accesses to > > sk->sk_shutdown in af_unix need be marked with READ_ONCE(). > > Let's not add READ_ONCE() if not needed. Othwewise, someone reading > the code would assess wrongly that the value could be updated locklessly > elsewhere. > > You can find all writers of sk->sk_shutdown do that update under > unix_state_lock(). > > > > Although > > there are additional reads in other->sk_shutdown without atomic reads, > > I'm excluding them as I'm uncertain about their potential parallel > > execution. > > > > Signed-off-by: Breno Leitao <leitao@debian.org> > > --- > > net/unix/af_unix.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c > > index 9a6ad5974dff..74795e6d13c6 100644 > > --- a/net/unix/af_unix.c > > +++ b/net/unix/af_unix.c > > @@ -2270,7 +2270,7 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg, > > goto out_err; > > } > > > > - if (sk->sk_shutdown & SEND_SHUTDOWN) > > + if (READ_ONCE(sk->sk_shutdown) & SEND_SHUTDOWN) > > goto pipe_err; > > > > while (sent < len) { > > @@ -2446,7 +2446,7 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size, > > unix_state_lock(sk); > > /* Signal EOF on disconnected non-blocking SEQPACKET socket. */ > > if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN && > > - (sk->sk_shutdown & RCV_SHUTDOWN)) > > + (READ_ONCE(sk->sk_shutdown) & RCV_SHUTDOWN)) > > Here we locked unix_state_lock() just before accessing sk_shutdown, > so no need for READ_ONCE(). > > > > err = 0; > > unix_state_unlock(sk); > > goto out; > > @@ -2566,7 +2566,7 @@ static long unix_stream_data_wait(struct sock *sk, long timeo, > > if (tail != last || > > (tail && tail->len != last_len) || > > sk->sk_err || > > - (sk->sk_shutdown & RCV_SHUTDOWN) || > > + (READ_ONCE(sk->sk_shutdown) & RCV_SHUTDOWN) || > > signal_pending(current) || > > !timeo) > > break; > > Same here, > > > > @@ -2764,7 +2764,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state, > > err = sock_error(sk); > > if (err) > > goto unlock; > > - if (sk->sk_shutdown & RCV_SHUTDOWN) > > + if (READ_ONCE(sk->sk_shutdown) & RCV_SHUTDOWN) > > goto unlock; > > > > unix_state_unlock(sk); > > and here. > > Could you update the changelog and repost v2 for unix_stream_sendmsg() > targetting net tree with this Fixes tag ?
Sure. I will keep the READ_ONCE only in unix_stream_sendmsg() then.
Thanks for the review!
| |