[PATCH 6.1 281/481] io_uring/kbuf: check if target buffer list is still legacy on recycle

Greg Kroah-Hartman
2026-03-23T16:21:14Z

6.1-stable review patch. If anyone has any objections, please let me know.

------------------

From: Jens Axboe <axboe@kernel.dk>

Commit c2c185be5c85d37215397c8e8781abf0a69bec1f upstream.

There's a gap between when the buffer was grabbed and when it
potentially gets recycled, where if the list is empty, someone could've
upgraded it to a ring provided type. This can happen if the request
is forced via io-wq. The legacy recycling is missing checking if the
buffer_list still exists, and if it's of the correct type. Add those
checks.

Cc: stable@vger.kernel.org
Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
Reported-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/kbuf.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -69,9 +69,15 @@ void io_kbuf_recycle_legacy(struct io_ki

buf = req->kbuf;
bl = io_buffer_get_list(ctx, buf->bgid);
- list_add(&buf->list, &bl->buf_list);
+ /*
+ * If the buffer list was upgraded to a ring-based one, or removed,
+ * while the request was in-flight in io-wq, drop it.
+ */
+ if (bl && !bl->buf_nr_pages)
+ list_add(&buf->list, &bl->buf_list);
req->flags &= ~REQ_F_BUFFER_SELECTED;
req->buf_index = buf->bgid;
+ req->kbuf = NULL;

io_ring_submit_unlock(ctx, issue_flags);
return;