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Date: Tue, 7 Jun 2022 22:23:37 +0800 From: Duoming Zhou <duoming@....edu.cn> To: linux-kernel@...r.kernel.org Cc: jreuter@...na.de, ralf@...ux-mips.org, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org, linux-hams@...r.kernel.org, thomas@...erried.de, Duoming Zhou <duoming@....edu.cn> Subject: [PATCH v2] net: ax25: Fix deadlock caused by skb_recv_datagram in ax25_recvmsg The skb_recv_datagram() in ax25_recvmsg() will hold lock_sock and block until it receives a packet from the remote. If the client doesn`t connect to server and calls read() directly, it will not receive any packets forever. As a result, the deadlock will happen. The fail log caused by deadlock is shown below: [ 369.606973] INFO: task ax25_deadlock:157 blocked for more than 245 seconds. [ 369.608919] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 369.613058] Call Trace: [ 369.613315] <TASK> [ 369.614072] __schedule+0x2f9/0xb20 [ 369.615029] schedule+0x49/0xb0 [ 369.615734] __lock_sock+0x92/0x100 [ 369.616763] ? destroy_sched_domains_rcu+0x20/0x20 [ 369.617941] lock_sock_nested+0x6e/0x70 [ 369.618809] ax25_bind+0xaa/0x210 [ 369.619736] __sys_bind+0xca/0xf0 [ 369.620039] ? do_futex+0xae/0x1b0 [ 369.620387] ? __x64_sys_futex+0x7c/0x1c0 [ 369.620601] ? fpregs_assert_state_consistent+0x19/0x40 [ 369.620613] __x64_sys_bind+0x11/0x20 [ 369.621791] do_syscall_64+0x3b/0x90 [ 369.622423] entry_SYSCALL_64_after_hwframe+0x46/0xb0 [ 369.623319] RIP: 0033:0x7f43c8aa8af7 [ 369.624301] RSP: 002b:00007f43c8197ef8 EFLAGS: 00000246 ORIG_RAX: 0000000000000031 [ 369.625756] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f43c8aa8af7 [ 369.626724] RDX: 0000000000000010 RSI: 000055768e2021d0 RDI: 0000000000000005 [ 369.628569] RBP: 00007f43c8197f00 R08: 0000000000000011 R09: 00007f43c8198700 [ 369.630208] R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff845e6afe [ 369.632240] R13: 00007fff845e6aff R14: 00007f43c8197fc0 R15: 00007f43c8198700 This patch moves the skb_recv_datagram() before lock_sock() in order that other functions that need lock_sock could be executed. Suggested-by: Thomas Osterried <thomas@...erried.de> Signed-off-by: Duoming Zhou <duoming@....edu.cn> Reported-by: Thomas Habets <thomas@@habets.se> --- Changes in v2: - Make commit messages clearer. net/ax25/af_ax25.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index 95393bb2760..02cd6087512 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -1665,6 +1665,11 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, int copied; int err = 0; + /* Now we can treat all alike */ + skb = skb_recv_datagram(sk, flags, &err); + if (!skb) + goto done; + lock_sock(sk); /* * This works for seqpacket too. The receiver has ordered the @@ -1675,11 +1680,6 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, goto out; } - /* Now we can treat all alike */ - skb = skb_recv_datagram(sk, flags, &err); - if (skb == NULL) - goto out; - if (!sk_to_ax25(sk)->pidincl) skb_pull(skb, 1); /* Remove PID */ @@ -1725,6 +1725,7 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, out: release_sock(sk); +done: return err; } -- 2.17.1
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