io_uring/zcrx: warn on freelist violations

The freelist is appropriately sized to always be able to take a free
niov, but let's be more defensive and check the invariant with a
warning. That should help to catch any double-free issues.

Suggested-by: Kai Aizen <kai@snailsploit.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://patch.msgid.link/2f3cea363b04649755e3b6bb9ab66485a95936d5.1776760901.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index 2eb09219f0a07d330973beb2a1b170257925bfce..7b93c87b8371b463b43e2dd88fe5617ee485c20d 100644 (file)
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -602,6 +602,8 @@ static void io_zcrx_return_niov_freelist(struct net_iov *niov)
        struct io_zcrx_area *area = io_zcrx_iov_to_area(niov);
 
        guard(spinlock_bh)(&area->freelist_lock);
+       if (WARN_ON_ONCE(area->free_count >= area->nia.num_niovs))
+               return;
        area->freelist[area->free_count++] = net_iov_idx(niov);
 }