[PATCH v2] io_uring/net: ensure compat import handlers clear free_iov

[Jens Axboe <axboe@kernel.dk>]

If we're not allocating the vectors because the count is below
UIO_FASTIOV, we still do need to properly clear ->free_iov to prevent
an erronous free of on-stack data.

Reported-by: Jiri Slaby <jirislaby@gmail.com>
Fixes: 4c17a496a7a0 ("io_uring/net: fix cleanup double free free_iov init")
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

v2: let's play it a bit safer and just always clear at the top rather
    in the individual cases.

diff --git a/io_uring/net.c b/io_uring/net.c
index 5229976cb582..f76b688f476e 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -494,6 +494,7 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
 	if (req->flags & REQ_F_BUFFER_SELECT) {
 		compat_ssize_t clen;
 
+		iomsg->free_iov = NULL;
 		if (msg.msg_iovlen == 0) {
 			sr->len = 0;
 		} else if (msg.msg_iovlen > 1) {

-- 
Jens Axboe