Messages in this thread | | | Date | Wed, 22 Mar 2023 10:01:16 +0100 | Subject | Re: [PATCH v4 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock | From | David Hildenbrand <> |
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On 22.03.23 09:54, David Hildenbrand wrote: > On 22.03.23 03:14, mawupeng wrote: >> >> >> On 2023/3/21 22:19, David Hildenbrand wrote: >>> On 21.03.23 08:44, mawupeng wrote: >>>> >>>> >>>> On 2023/3/20 18:54, David Hildenbrand wrote: >>>>> On 20.03.23 03:47, Wupeng Ma wrote: >>>>>> From: Ma Wupeng <mawupeng1@huawei.com> >>>>>> >>>>>> 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 >>>> >>> >>> I was asking about addr=0, len=ULONG_MAX. >>> >>> IIUC, that used to work but could now fail? I haven't played with it, though. >> >> Thanks for reviewing. >> >> Previous for add = 0 and len == ULONG_MAX, mlock will return ok(0) since len overflows to zero. >> IFAICT, this is not right since mlock do noting(lock nothing) and return ok(0). >> >> With this patch, for the same situation, mlock can return EINVAL as expected. > > Quoting the man page: > > "EINVAL (mlock(), mlock2(), and munlock()) The result of the addition > addr+len was less than addr (e.g., the addition may have resulted in an > overflow)." > > ULONG_MAX+0 = ULONG_MAX > > There is no overflow expected. The proper way to implement it would be > to handle that case and not fail with EINVAL. > > At least that would be expected when reading the man page. >
As a side note, I agree that failing with EINVAL is better than doing noting (mlocking nothing). But I am not sure what we are expected to do in that case ... the man page is a bit vague on that.
-- Thanks,
David / dhildenb
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