Re: [PATCH] rbd: check snap_count against RBD_MAX_SNAP_COUNT

[Alex Elder <elder@ieee.org>]

On 5/29/26 8:12 PM, Rosen Penev wrote:
> snap_count is u32 but the comparison is against a SIZE_MAX-derived value
> (~2^61 on 64-bit), which clang flags as always false with
> -Wtautological-constant-out-of-range-compare.
> 
> The proper check here should be that snap_count does not go over
> RBD_MAX_SNAP_COUNT.
> 
> Assisted-by: Opencode:Big-pickle
> Signed-off-by: Rosen Penev <rosenp@gmail.com>

Looks good to me.

Reviewed-by: Alex Elder <elder@riscstar.com>

> ---
>   drivers/block/rbd.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 94709466ad19..25215c209484 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -6075,12 +6075,9 @@ static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev,
>   
>   	/*
>   	 * Make sure the reported number of snapshot ids wouldn't go
> -	 * beyond the end of our buffer.  But before checking that,
> -	 * make sure the computed size of the snapshot context we
> -	 * allocate is representable in a size_t.
> +	 * beyond the end of our buffer.
>   	 */
> -	if (snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context))
> -				 / sizeof (u64)) {
> +	if (snap_count > RBD_MAX_SNAP_COUNT) {
>   		ret = -EINVAL;
>   		goto out;
>   	}