Messages in this thread | | | Date | Wed, 8 Feb 2023 14:51:08 +0100 | Subject | Re: [PATCH v3 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock | From | David Hildenbrand <> |
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On 07.02.23 02:24, mawupeng wrote: > > > On 2023/2/7 1:05, David Hildenbrand wrote: >> On 06.02.23 01:48, mawupeng wrote: >>> >>> >>> On 2023/2/4 1:14, David Hildenbrand wrote: >>>> On 28.01.23 07:32, 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. >>>>> >>>>> Return 0 early to avoid burn a bunch of cpu cycles if len == 0. >>>>> >>>>> Signed-off-by: Ma Wupeng <mawupeng1@huawei.com> >>>>> --- >>>>> mm/mlock.c | 14 ++++++++++++-- >>>>> 1 file changed, 12 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/mm/mlock.c b/mm/mlock.c >>>>> index 7032f6dd0ce1..eb09968ba27f 100644 >>>>> --- a/mm/mlock.c >>>>> +++ b/mm/mlock.c >>>>> @@ -478,8 +478,6 @@ static int apply_vma_lock_flags(unsigned long start, size_t len, >>>>> end = start + len; >>>>> if (end < start) >>>>> return -EINVAL; >>>>> - if (end == start) >>>>> - return 0; >>>>> vma = mas_walk(&mas); >>>>> if (!vma) >>>>> return -ENOMEM; >>>>> @@ -575,7 +573,13 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla >>>>> if (!can_do_mlock()) >>>>> return -EPERM; >>>>> + if (!len) >>>>> + return 0; >>>>> + >>>>> len = PAGE_ALIGN(len + (offset_in_page(start))); >>>>> + if (!len) >>>>> + return -EINVAL; >>>>> + >>>>> start &= PAGE_MASK; >>>> >>>> The "ordinary" overflows are detected in apply_vma_lock_flags(), correct? >>> >>> Overflow is not checked anywhere however the ordinary return early if len == 0 is detected in apply_vma_lock_flags(). >>> >> >> I meant the >> >> end = start + len; >> if (end < start) >> return -EINVAL; >> >> Essentially, what I wanted to double-check is that with your changes, we catch all kinds of overflows as documented in the man page, correct? > > Oh i see. You are right, The "ordinary" overflows are detected for mlock/munlock in apply_vma_lock_flags(). > > Yes, we may need to update the man page for all these four syscalls.
E.g., mlock() already documents "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)."
Just to rephrase my question what I wanted to double-check: are we now identifying all such overflows or are you aware of other corner cases?
-- Thanks,
David / dhildenb
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