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

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Message-Id: <20230207012046.8683-1-tung.q.nguyen@dektech.com.au>
Date:   Tue,  7 Feb 2023 01:20:46 +0000
From:   Tung Nguyen <tung.q.nguyen@...tech.com.au>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
        pabeni@...hat.com, jmaloy@...hat.com, ying.xue@...driver.com,
        viro@...iv.linux.org.uk,
        syzbot+d43608d061e8847ec9f3@...kaller.appspotmail.com
Subject: [PATCH net 1/1] tipc: fix kernel warning when sending SYN message

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@...kaller.appspotmail.com
Acked-by: Jon Maloy <jmaloy@...hat.com>
Signed-off-by: Tung Nguyen <tung.q.nguyen@...tech.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