When nr_segs equal to zero in iovec_from_user, the object msg->msg_iter.iov is uninit stack memory in caif_seqpkt_sendmsg which is defined in ___sys_sendmsg. So we cann't just judge msg->msg_iter.iov->base directlly. We can use nr_segs to judge msg in caif_seqpkt_sendmsg whether has data buffers.

===================================================== BUG: KMSAN: uninit-value in caif_seqpkt_sendmsg+0x693/0xf60 net/caif/caif_socket.c:542 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c9/0x220 lib/dump_stack.c:118 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118 __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215 caif_seqpkt_sendmsg+0x693/0xf60 net/caif/caif_socket.c:542 sock_sendmsg_nosec net/socket.c:652 [inline] sock_sendmsg net/socket.c:672 [inline] ____sys_sendmsg+0x12b6/0x1350 net/socket.c:2343 ___sys_sendmsg net/socket.c:2397 [inline] __sys_sendmmsg+0x808/0xc90 net/socket.c:2480 __compat_sys_sendmmsg net/compat.c:656 [inline]

Reported-by: syzbot+09a5d591c1f98cf5efcb@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=1ace85e8fc9b0d5a45c08c2656c3e91762daa9b... Fixes: bece7b2398d0 ("caif: Rewritten socket implementation") Signed-off-by: Ziyang Xuan william.xuanziyang@huawei.com --- net/caif/caif_socket.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c index 647554c..e12fd3c 100644 --- a/net/caif/caif_socket.c +++ b/net/caif/caif_socket.c @@ -539,7 +539,8 @@ static int caif_seqpkt_sendmsg(struct socket *sock, struct msghdr *msg, goto err;

ret = -EINVAL; - if (unlikely(msg->msg_iter.iov->iov_base == NULL)) + if (unlikely(msg->msg_iter.nr_segs == 0) || + unlikely(msg->msg_iter.iov->iov_base == NULL)) goto err; noblock = msg->msg_flags & MSG_DONTWAIT;