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SubjectRe: [PATCH v4 2/4] mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check
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On 2/3/22 10:46, Vlastimil Babka wrote:
> On 2/2/22 21:30, Waiman Long wrote:
>> The snprintf() function can return a length greater than the given
>> input size. That will require a check for buffer overrun after each
>> invocation of snprintf(). scnprintf(), on the other hand, will never
>> return a greater length. By using scnprintf() in selected places, we
>> can avoid some buffer overrun checks except after stack_depot_snprint()
>> and after the last snprintf().
>>
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> Acked-by: David Rientjes <rientjes@google.com>
>> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Looks like this will work, but note that if the purpose of patch 1/4 was
> that after the first scnprintf() that overflows the following calls will be
> short-cut thanks to passing the size as 0, AFAICS that won't work. Because
> scnprintf() returns the number without trailing zero, 'ret' will be 'count -
> 1' after the overflow, so 'count - ret' will be 1, never 0.

Yes, I am aware of that. Patch 1 is just a micro-optimization for the
very rare case.

Cheers,
Longman


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