netdev - [PATCH net] sctp: not free the new asoc when sctp_wait_for

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Message-Id: <6ee31cce8c2e36a7e189de11c13c257e8c45b42f.1539716772.git.lucien.xin@gmail.com>
Date:   Wed, 17 Oct 2018 03:06:12 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org
Cc:     davem@...emloft.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>
Subject: [PATCH net] sctp: not free the new asoc when sctp_wait_for_connect returns err

When sctp_wait_for_connect is called to wait for connect ready
for sp->strm_interleave in sctp_sendmsg_to_asoc, a panic could
be triggered if cpu is scheduled out and the new asoc is freed
elsewhere, as it will return err and later the asoc gets freed
again in sctp_sendmsg.

[  285.840764] list_del corruption, ffff9f0f7b284078->next is LIST_POISON1 (dead000000000100)
[  285.843590] WARNING: CPU: 1 PID: 8861 at lib/list_debug.c:47 __list_del_entry_valid+0x50/0xa0
[  285.846193] Kernel panic - not syncing: panic_on_warn set ...
[  285.846193]
[  285.848206] CPU: 1 PID: 8861 Comm: sctp_ndata Kdump: loaded Not tainted 4.19.0-rc7.label #584
[  285.850559] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[  285.852164] Call Trace:
...
[  285.872210]  ? __list_del_entry_valid+0x50/0xa0
[  285.872894]  sctp_association_free+0x42/0x2d0 [sctp]
[  285.873612]  sctp_sendmsg+0x5a4/0x6b0 [sctp]
[  285.874236]  sock_sendmsg+0x30/0x40
[  285.874741]  ___sys_sendmsg+0x27a/0x290
[  285.875304]  ? __switch_to_asm+0x34/0x70
[  285.875872]  ? __switch_to_asm+0x40/0x70
[  285.876438]  ? ptep_set_access_flags+0x2a/0x30
[  285.877083]  ? do_wp_page+0x151/0x540
[  285.877614]  __sys_sendmsg+0x58/0xa0
[  285.878138]  do_syscall_64+0x55/0x180
[  285.878669]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

This is a similar issue with the one fixed in Commit ca3af4dd28cf
("sctp: do not free asoc when it is already dead in sctp_sendmsg").
But this one can't be fixed by returning -ESRCH for the dead asoc
in sctp_wait_for_connect, as it will break sctp_connect's return
value to users.

This patch is to simply set err to -ESRCH before it returns to
sctp_sendmsg when any err is returned by sctp_wait_for_connect
for sp->strm_interleave, so that no asoc would be freed due to
this.

When users see this error, they will know the packet hasn't been
sent. And it also makes sense to not free asoc because waiting
connect fails, like the second call for sctp_wait_for_connect in
sctp_sendmsg_to_asoc.

Fixes: 668c9beb9020 ("sctp: implement assign_number for sctp_stream_interleave")
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/sctp/socket.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index e25a20f..1baa9d9 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1946,8 +1946,10 @@ static int sctp_sendmsg_to_asoc(struct sctp_association *asoc,
 		if (sp->strm_interleave) {
 			timeo = sock_sndtimeo(sk, 0);
 			err = sctp_wait_for_connect(asoc, &timeo);
-			if (err)
+			if (err) {
+				err = -ESRCH;
 				goto err;
+			}
 		} else {
 			wait_connect = true;
 		}
-- 
2.1.0