[PATCH RESEND 2/2] 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: 4fe2c963154c ("io_uring: add support for link with drain")
Signed-off-by: Jackie Liu <liuyu...@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 42a684e..1621243 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2357,6 +2357,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, struct 
sqe_submit *sqes,
                        io_queue_link_head(ctx, link, &link->submit, shadow_req,
                                                true);
                        link = NULL;
+                       shadow_req = NULL;
                }
                prev_was_link = (sqes[i].sqe->flags & IOSQE_IO_LINK) != 0;
 
@@ -2543,6 +2544,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, 
unsigned int to_submit,
                        io_queue_link_head(ctx, link, &link->submit, shadow_req,
                                                force_nonblock);
                        link = NULL;
+                       shadow_req = NULL;
                }
                prev_was_link = (s.sqe->flags & IOSQE_IO_LINK) != 0;
 
-- 
2.7.4