[PATCH v5] fuse: clear ent->fuse_req in commit_fetch error path

[Bernd Schubert via B4 Relay]

From: Zhenghang Xiao <kipreyyy@xxxxxxxxx>

fuse_uring_commit_fetch() error path called fuse_request_end(req) without
clearing ent->fuse_req when fuse_ring_ent_set_commit() fails. The
still-pending fuse_uring_send_in_task() task-work later dereferences the
dangling pointer through fuse_uring_prepare_send(), causing a
use-after-free.

End the request with fuse_uring_req_end(), which handles all conditions
already.

Annotation/edition by Bernd: The UAF should be fixed by other means already
and actually has to be avoided that way.
Just checking for ent->fuse_req == NULL in fuse_uring_send_in_task()
would be prone to race conditions, because if malicious userspace
would commit requests that have passed the NULL check, but are
in doing args copy, it would still trigger a use-after-free.
Setting ent->fuse_req = NULL in fuse_uring_commit_fetch() still
makes sense, though.

Reported-by: Shuvam Pandey <shuvampandey1@xxxxxxxxx>
Reported-by: Berkant Koc <me@xxxxxxxxxx>
Signed-off-by: Zhenghang Xiao <kipreyyy@xxxxxxxxx>
Signed-off-by: Bernd Schubert <bernd@xxxxxxxxxxx>
---
This is to fix race conditions reported by Berkant and Zhenghang.

Changes in v5:
- Rebased against Miklos' for-next branch - all except one patch already
  picked up
- Use fuse_uring_req_end() instead of hand coding what it does
---
 fs/fuse/dev_uring.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index ba5edf5d01b3..77c8cec43d9c 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -1003,9 +1003,7 @@ static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
 		pr_info_ratelimited("qid=%d commit_id %llu state %d",
 				    queue->qid, commit_id, ent->state);
 		spin_unlock(&queue->lock);
-		req->out.h.error = err;
-		clear_bit(FR_SENT, &req->flags);
-		fuse_request_end(req);
+		fuse_uring_req_end(ent, req, err);
 		return err;
 	}
 

---
base-commit: bb43b4c7ea2a8265141aa93240f3f0ca71d85c0e
change-id: 20260518-fuse-io-uring-race-fixes-59760420d2ae

Best regards,
--  
Bernd Schubert <bernd@xxxxxxxxxxx>