[PATCH net 1/1] tipc: fix kernel warning when sending SYN message

* [PATCH net 1/1] tipc: fix kernel warning when sending SYN message
@ 2023-02-07  1:20 Tung Nguyen
  2023-02-08  5:34 ` Jakub Kicinski
  0 siblings, 1 reply; 4+ messages in thread
From: Tung Nguyen @ 2023-02-07  1:20 UTC (permalink / raw)
  To: netdev
  Cc: davem, kuba, edumazet, pabeni, jmaloy, ying.xue, viro,
	syzbot+d43608d061e8847ec9f3

When sending a SYN message, this kernel stack trace is observed:

...
[   13.396352] RIP: 0010:_copy_from_iter+0xb4/0x550
...
[   13.398494] Call Trace:
[   13.398630]  <TASK>
[   13.398630]  ? __alloc_skb+0xed/0x1a0
[   13.398630]  tipc_msg_build+0x12c/0x670 [tipc]
[   13.398630]  ? shmem_add_to_page_cache.isra.71+0x151/0x290
[   13.398630]  __tipc_sendmsg+0x2d1/0x710 [tipc]
[   13.398630]  ? tipc_connect+0x1d9/0x230 [tipc]
[   13.398630]  ? __local_bh_enable_ip+0x37/0x80
[   13.398630]  tipc_connect+0x1d9/0x230 [tipc]
[   13.398630]  ? __sys_connect+0x9f/0xd0
[   13.398630]  __sys_connect+0x9f/0xd0
[   13.398630]  ? preempt_count_add+0x4d/0xa0
[   13.398630]  ? fpregs_assert_state_consistent+0x22/0x50
[   13.398630]  __x64_sys_connect+0x16/0x20
[   13.398630]  do_syscall_64+0x42/0x90
[   13.398630]  entry_SYSCALL_64_after_hwframe+0x63/0xcd

It is because commit a41dad905e5a ("iov_iter: saner checks for attempt
to copy to/from iterator") has introduced sanity check for copying
from/to iov iterator. Lacking of copy direction from the iterator
viewpoint would lead to kernel stack trace like above.

This commit fixes this issue by initializing the iov iterator with
the correct copy direction.

Reported-by: syzbot+d43608d061e8847ec9f3@syzkaller.appspotmail.com
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Tung Nguyen <tung.q.nguyen@dektech.com.au>
---
 net/tipc/msg.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 5c9fd4791c4b..cce118fea07a 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -381,6 +381,9 @@ int tipc_msg_build(struct tipc_msg *mhdr, struct msghdr *m, int offset,
 
 	msg_set_size(mhdr, msz);
 
+	if (!dsz)
+		iov_iter_init(&m->msg_iter, ITER_SOURCE, NULL, 0, 0);
+
 	/* No fragmentation needed? */
 	if (likely(msz <= pktmax)) {
 		skb = tipc_buf_acquire(msz, GFP_KERNEL);
-- 
2.34.1


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