io_uring: check for rollover of buffer ID when providing buffers

We already check if the chosen starting offset for the buffer IDs fit
within an unsigned short, as 65535 is the maximum value for a provided
buffer. But if the caller asks to add N buffers at offset M, and M + N
would exceed the size of the unsigned short, we simply add buffers with
wrapping around the ID.

This is not necessarily a bug and could in fact be a valid use case, but
it seems confusing and inconsistent with the initial check for starting
offset. Let's check for wrap consistently, and error the addition if we
do need to wrap.

Reported-by: Olivier Langlois <olivier@trillion01.com>
Link: https://github.com/axboe/liburing/issues/726
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 25cd724ade184ac452463d18e134d7e3ae469503..e2c46889d5fab614dbeb6b26a8a696d778709b8d 100644 (file)
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -346,6 +346,8 @@ 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)
+               return -EINVAL;
        p->bid = tmp;
        return 0;
 }