[PATCH 2/2] ax25: Fix deadlock hang during concurrent read and write on socket.
STALE1819d
From: Ralf Baechle <hidden>
Date: 2021-10-12 20:20:58
Also in:
linux-hams
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Thomas Habets <redacted> Before this patch, this hangs, because the read(2) blocks the write(2). Before: strace -f -eread,write ./examples/client_lockcheck M0THC-9 M0THC-0 M0THC-2 strace: Process 3888 attached [pid 3888] read(3, <unfinished ...> [pid 3887] write(3, "hello world", 11 [hang] After: strace -f -eread,write ./examples/client_lockcheck M0THC-9 M0THC-0 M0THC-2 strace: Process 2433 attached [pid 2433] read(3, <unfinished ...> [pid 2432] write(3, "hello world", 11) = 11 [pid 2433] <... read resumed> "yo", 1000) = 2 [pid 2433] write(1, "yo\n", 3yo ) = 3 [successful exit] Signed-off-by: Thomas Habets <redacted> Signed-off-by: Ralf Baechle <redacted> --- net/ax25/af_ax25.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 5e7ab76f7f9b..d2d0dd744bb4 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c@@ -1624,22 +1624,22 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, int copied; int err = 0; - lock_sock(sk); /* * This works for seqpacket too. The receiver has ordered the * queue for us! We do one quick check first though */ if (sk->sk_type == SOCK_SEQPACKET && sk->sk_state != TCP_ESTABLISHED) { err = -ENOTCONN; - goto out; + goto out_nolock; } /* Now we can treat all alike */ skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT, flags & MSG_DONTWAIT, &err); if (skb == NULL) - goto out; + goto out_nolock; + lock_sock(sk); if (!sk_to_ax25(sk)->pidincl) skb_pull(skb, 1); /* Remove PID */
@@ -1684,6 +1684,7 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, out: release_sock(sk); +out_nolock: return err; }
--
2.31.1