Messages in this thread | | | Date | Wed, 8 Jun 2022 09:02:10 +0800 (GMT+08:00) | From | duoming@zju ... | Subject | Re: [PATCH v2] net: ax25: Fix deadlock caused by skb_recv_datagram in ax25_recvmsg |
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Hello,
On Tue, 7 Jun 2022 10:06:27 -0700 Eric Dumazet wrote:
> On Tue, Jun 7, 2022 at 7:24 AM Duoming Zhou <duoming@zju.edu.cn> wrote: > > > > 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@osterried.de> > > Signed-off-by: Duoming Zhou <duoming@zju.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; > > + > > So at this point we have skb=something. This means that the following > branch will leak it. > > if (sk->sk_type == SOCK_SEQPACKET && sk->sk_state != TCP_ESTABLISHED) { > err = -ENOTCONN; > goto out; // skb will be leaked > } >
Thank your for pointing out the problem! I will add skb_free_datagram() before goto out in order to mitigate the memory leak.
if (sk->sk_type == SOCK_SEQPACKET && sk->sk_state != TCP_ESTABLISHED) { err = -ENOTCONN; + skb_free_datagram(sk, skb); goto out; }
Best regards, Duoming Zhou
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