Re: [PATCH v4 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock

[mawupeng]

On 2023/3/20 18:54, David Hildenbrand wrote:
> On 20.03.23 03:47, Wupeng Ma wrote:
>> From: Ma Wupeng <mawupeng1@xxxxxxxxxx>
>>
>> While testing mlock, we have a problem if the len of mlock is ULONG_MAX.
>> The return value of mlock is zero. But nothing will be locked since the
>> len in do_mlock overflows to zero due to the following code in mlock:
>>
>>    len = PAGE_ALIGN(len + (offset_in_page(start)));
>>
>> The same problem happens in munlock.
>>
>> Add new check and return -EINVAL to fix this overflowing scenarios since
>> they are absolutely wrong.
> 
> Thinking again, wouldn't we reject mlock(0, ULONG_MAX) now as well?

mlock will return 0 if len is zero which is the same w/o this patchset.
Here is the calltrace if len is zero.

mlock(len == 0)
	do_mlock(len == 0)
		if (!len)
			return 0
			
Sorry for wasting your time in the wrong v4. Here is the latest v5:

  https://patchwork.kernel.org/project/linux-mm/list/?series=732216

> 
>>
>> Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
>> ---
>>   mm/mlock.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/mm/mlock.c b/mm/mlock.c
>> index 617469fce96d..eb68476da497 100644
>> --- a/mm/mlock.c
>> +++ b/mm/mlock.c
>> @@ -568,6 +568,7 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
>>       unsigned long locked;
>>       unsigned long lock_limit;
>>       int error = -ENOMEM;
>> +    size_t old_len = len;
>>         start = untagged_addr(start);
>>   @@ -577,6 +578,9 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
>>       len = PAGE_ALIGN(len + (offset_in_page(start)));
>>       start &= PAGE_MASK;
>>   +    if (old_len != 0 && len == 0)
> 
> if (old_len && !len)
> 
>> +        return -EINVAL;
>> +
>>       lock_limit = rlimit(RLIMIT_MEMLOCK);
>>       lock_limit >>= PAGE_SHIFT;
>>       locked = len >> PAGE_SHIFT;
>> @@ -631,12 +635,16 @@ SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
>>   SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
>>   {
>>       int ret;
>> +    size_t old_len = len;
>>         start = untagged_addr(start);
>>         len = PAGE_ALIGN(len + (offset_in_page(start)));
>>       start &= PAGE_MASK;
>>   +    if (old_len != 0 && len == 0)
> 
> if (old_len && !len)
> 
>> +        return -EINVAL;
>> +
>>       if (mmap_write_lock_killable(current->mm))
>>           return -EINTR;
>>       ret = apply_vma_lock_flags(start, len, 0);
>