io_uring/kbuf: Fix check of BID wrapping in provided buffers

[ 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@suse.de>
Link: https://lore.kernel.org/r/20231005000531.30800-2-krisman@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index acc37e5..e45602b 100644 (file)
--- 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;