Messages in this thread | | | Date | Wed, 22 Mar 2023 12:27:40 +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 10:20, mawupeng wrote: > > > On 2023/3/22 17:01, David Hildenbrand wrote: >> 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 for you reviewing. > > Can we try to expand the man page since overflow is considered in man page?
I guess we could spell out that Linux aligns the length up to the next page boundary, and that overflow checks are performed on this aligned length.
-- Thanks,
David / dhildenb
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