[PATCH 6.1 139/379] io_uring/kbuf: Fix check of BID wrapping in provided buffers

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

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

From: Gabriel Krisman Bertazi <krisman@xxxxxxx>

[ Upstream commit ab69838e7c75b0edb699c1a8f42752b30333c46f ]

Commit 3851d25c75ed0 ("io_uring: check for rollover of buffer ID when
providing buffers") introduced a check to prevent wrapping the BID
counter when sqe->off is provided, but it's off-by-one too
restrictive, rejecting the last possible BID (65534).

i.e., the following fails with -EINVAL.

     io_uring_prep_provide_buffers(sqe, addr, size, 0xFFFF, 0, 0);

Fixes: 3851d25c75ed ("io_uring: check for rollover of buffer ID when providing buffers")
Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxx>
Link: https://lore.kernel.org/r/20231005000531.30800-2-krisman@xxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 io_uring/kbuf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index acc37e5a6d4e1..e45602b02a9f1 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -347,7 +347,7 @@ int io_provide_buffers_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
 	tmp = READ_ONCE(sqe->off);
 	if (tmp > USHRT_MAX)
 		return -E2BIG;
-	if (tmp + p->nbufs >= USHRT_MAX)
+	if (tmp + p->nbufs > USHRT_MAX)
 		return -EINVAL;
 	p->bid = tmp;
 	return 0;
-- 
2.42.0






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