[tipc-discussion] [PATCH v1 1/1] tipc: fix kernel warning when sending SYN message

[Tung N. <tun...@de...>]

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.

Signed-off-by: Tung Nguyen <tun...@de...>
---
 net/tipc/msg.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/tipc/msg.c b/net/tipc/msg.c
index 5c9fd4791c4b..f40cd9032b62 100644
--- a/net/tipc/msg.c
+++ b/net/tipc/msg.c
@@ -377,10 +377,14 @@ int tipc_msg_build(struct tipc_msg *mhdr, struct msghdr *m, int offset,
 	int pktno = 1;
 	char *pktpos;
 	int pktsz;
+	struct iovec iov;
 	int rc;
 
 	msg_set_size(mhdr, msz);
 
+	if (!dsz)
+		iov_iter_init(&m->msg_iter, ITER_SOURCE, &iov, 0, 0);
+
 	/* No fragmentation needed? */
 	if (likely(msz <= pktmax)) {
 		skb = tipc_buf_acquire(msz, GFP_KERNEL);
-- 
2.34.1