On 2023/2/4 1:14, David Hildenbrand wrote: > On 28.01.23 07:32, 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. >> >> Return 0 early to avoid burn a bunch of cpu cycles if len == 0. >> >> Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx> >> --- >> 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(). do_mlock apply_vma_lock_flags end = start + len; if (end == start) return 0; Move the checking to the begin is easier to detect overflows and make the logic clearer and avoid burn a bunch of cpu cycles. >
