Re: [PATCH v3 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock

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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@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().


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?

--
Thanks,

David / dhildenb





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