io_uring: limit size of provided buffer ring

The type of head and tail do not allow more than 2^15 entries in a
provided buffer ring, so do not allow this.
At 2^16 while each entry can be indexed, there is no way to
disambiguate full vs empty.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220613101157.3687-4-dylany@fb.com
Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6eea18e..85b116d 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -13002,6 +13002,10 @@ static int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
        if (!is_power_of_2(reg.ring_entries))
                return -EINVAL;
 
+       /* cannot disambiguate full vs empty due to head/tail size */
+       if (reg.ring_entries >= 65536)
+               return -EINVAL;
+
        if (unlikely(reg.bgid < BGID_ARRAY && !ctx->io_bl)) {
                int ret = io_init_bl_list(ctx);
                if (ret)