[Devel] [PATCH vz10 07/24] blk-cbt: don't WARN on a user-supplied ABI version mismatch

[Andrey Zhadchenko]

I don't like that. Customers do not run with panic_on_warn. If this 
fails in our test environment, that's actually great (it means something 
went very wrong). pr_warn_ratelimited is worse than WARN_ONCE regarding 
intentional spamming.

On 7/6/26 12:59, Konstantin Khorenko wrote:
> blk_cbt_ioctl() reads abi_version straight from the ioctl argument and
> WARN_ONCE()s if it does not match CBT_ABI_VERSION. The value is fully
> userspace-controlled, so any process issuing a BLKCBT* ioctl with a
> stale/newer struct taints the kernel, dumps a backtrace, and can panic a
> host that runs with panic_on_warn. Downgrade to pr_warn_ratelimited();
> the -EOPNOTSUPP return is the actual contract.
> 
> Fixes: 6e42f62a2c88 ("block/blk-cbt: introduce ABI versioning")
> Feature: cbt: changed block tracking (for backup)
> https://virtuozzo.atlassian.net/browse/VSTOR-137234
> Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
> ---
>   block/blk-cbt.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-cbt.c b/block/blk-cbt.c
> index 90219f58f1ae..91a888770411 100644
> --- a/block/blk-cbt.c
> +++ b/block/blk-cbt.c
> @@ -1093,8 +1093,8 @@ int blk_cbt_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
>   		return -EFAULT;
>   
>   	if (abi_version != CBT_ABI_VERSION) {
> -		WARN_ONCE(1, "blk-cbt ABI mimatch: kernel has %d, userspace uses %d",
> -			  CBT_ABI_VERSION, abi_version);
> +		pr_warn_ratelimited("blk-cbt: ABI mismatch: kernel has %d, userspace uses %d\n",
> +				    CBT_ABI_VERSION, abi_version);
>   		return -EOPNOTSUPP;
>   	}
>