[SRU OEM-6.1 4/4] io_uring/msg_ring: fix missing lock on overflow for IOPOLL

[Thadeu Lima de Souza Cascardo]

From: Jens Axboe <axboe at kernel.dk>

If the target ring is configured with IOPOLL, then we always need to hold
the target ring uring_lock before posting CQEs. We could just grab it
unconditionally, but since we don't expect many target rings to be of this
type, make grabbing the uring_lock conditional on the ring type.

Link: https://lore.kernel.org/io-uring/Y8krlYa52%2F0YGqkg@ip-172-31-85-199.ec2.internal/
Reported-by: Xingyuan Mo <hdthky0 at gmail.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(backported from commit e12d7a46f65ae4b7d58a5e0c1cbfa825cf8d830d)
[cascardo: no io_msg_tw_complete and io_post_aux_cqe still gets an overflow parameter]
CVE-2023-2430
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 io_uring/msg_ring.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index 59a0e5f9fdf9..e0250cec0133 100644
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -57,20 +57,29 @@ void io_msg_ring_cleanup(struct io_kiocb *req)
 	msg->src_file = NULL;
 }
 
-static int io_msg_ring_data(struct io_kiocb *req)
+static int io_msg_ring_data(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_ring_ctx *target_ctx = req->file->private_data;
 	struct io_msg *msg = io_kiocb_to_cmd(req, struct io_msg);
+	int ret;
 
 	if (msg->src_fd || msg->dst_fd || msg->flags)
 		return -EINVAL;
 	if (target_ctx->flags & IORING_SETUP_R_DISABLED)
 		return -EBADFD;
 
-	if (io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0, true))
-		return 0;
-
-	return -EOVERFLOW;
+	ret = -EOVERFLOW;
+	if (target_ctx->flags & IORING_SETUP_IOPOLL) {
+		if (unlikely(io_double_lock_ctx(target_ctx, issue_flags)))
+			return -EAGAIN;
+		if (io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0, true))
+			ret = 0;
+		io_double_unlock_ctx(target_ctx);
+	} else {
+		if (io_post_aux_cqe(target_ctx, msg->user_data, msg->len, 0, true))
+			ret = 0;
+	}
+	return ret;
 }
 
 static struct file *io_msg_grab_file(struct io_kiocb *req, unsigned int issue_flags)
@@ -179,7 +188,7 @@ int io_msg_ring(struct io_kiocb *req, unsigned int issue_flags)
 
 	switch (msg->cmd) {
 	case IORING_MSG_DATA:
-		ret = io_msg_ring_data(req);
+		ret = io_msg_ring_data(req, issue_flags);
 		break;
 	case IORING_MSG_SEND_FD:
 		ret = io_msg_send_fd(req, issue_flags);
-- 
2.34.1