[PATCH] io_uring: fix use-after-free of shadow_req

[PATCH] io_uring: fix use-after-free of shadow_req

[Jackie Liu]

There is a potential dangling pointer problem. we never clean
shadow_req, if there are multiple link lists in this series of
sqes, then the shadow_req will not reallocate, and continue to
use the last one. but in the previous, his memory has been
released, thus forming a dangling pointer. let's clean up him
and make sure that every new link list can reapply for a new
shadow_req.

Fixes: 4fe2c96315 ("io_uring: add support for link with drain")
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b03630ced9ae..45ed66d17a64 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2341,6 +2341,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, struct sqe_submit *sqes,
 		if (!prev_was_link && link) {
 			io_queue_link_head(ctx, link, &link->submit, shadow_req);
 			link = NULL;
+			shadow_req = NULL;
 		}
 		prev_was_link = (sqes[i].sqe->flags & IOSQE_IO_LINK) != 0;
 
@@ -2524,6 +2525,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 		if (!prev_was_link && link) {
 			io_queue_link_head(ctx, link, &link->submit, shadow_req);
 			link = NULL;
+			shadow_req = NULL;
 		}
 		prev_was_link = (s.sqe->flags & IOSQE_IO_LINK) != 0;
 
-- 
2.23.0