io_uring: add build check for buf_index overflows

req->buf_index is u16 and so we rely on registered buffers indexes
fitting into it. Add a build check, so when the upper limit for the
number of buffers is lifted we get a compliation fail but not lurking
problems.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/787e8e1a17cea51ca6301426b1c4c4887b8bd676.1629920396.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 09194f7276babf67a76f50e4bd9d7ce21d825e07..53326449d68563a36a78451b4e9659d0e93fb8c4 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -10493,6 +10493,10 @@ static int __init io_uring_init(void)
                     sizeof(struct io_uring_rsrc_update));
        BUILD_BUG_ON(sizeof(struct io_uring_rsrc_update) >
                     sizeof(struct io_uring_rsrc_update2));
+
+       /* ->buf_index is u16 */
+       BUILD_BUG_ON(IORING_MAX_REG_BUFFERS >= (1u << 16));
+
        /* should fit into one byte */
        BUILD_BUG_ON(SQE_VALID_FLAGS >= (1 << 8));