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

[Andrey Zhadchenko]

Probably spitting WARNs on user supplied output looks more like a debug 
approach. So if this WARN_ONCE is breaking some tests we should just 
remove that instead of changing it into pr_warn_ratelimited.

On 7/6/26 14:11, Andrey Zhadchenko wrote:
> 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;
>>       }
> 
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