Re: [PATCH v4 2/2] mm/userfaultfd: add VM_WARN_ONCE()

[Muhammad Usama Anjum <usama.anjum@collabora.com>]

On 2/16/23 2:24 PM, David Hildenbrand wrote:
> On 16.02.23 10:16, Muhammad Usama Anjum wrote:
>> Add VM_WARN_ONCE() to uffd_wp_range() to detect range (start, len) abuse.
>>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
>> ---
>>   mm/userfaultfd.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
>> index 77c5839e591c..d89ed44d2668 100644
>> --- a/mm/userfaultfd.c
>> +++ b/mm/userfaultfd.c
>> @@ -717,6 +717,8 @@ long uffd_wp_range(struct mm_struct *dst_mm, struct
>> vm_area_struct *dst_vma,
>>       struct mmu_gather tlb;
>>       long ret;
>>   +    VM_WARN_ONCE(start < dst_vma->vm_start || start + len >
>> dst_vma->vm_end,
>> +             "The address range exceeds VMA boundary.\n");
> 
> VM_WARN_ON_ONCE is sufficient (sorry for spelling out the wrong variant
> earlier).
Will do in the next version. Thanks.

> 
> These kinds of bugs are expected to be found early during testing, still it
> might make sense to implement a backup path
> 
> if (WARN_ON_ONCE(...))
>     return -EINVAL;
> 
> But we can't use VM_WARN_ON_ONCE here, so we can't compile it out anymore
> ... so I guess a simple VM_WARN_ON_ONCE() is sufficient.
> 

-- 
BR,
Muhammad Usama Anjum