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

lock_limit = rlimit(RLIMIT_MEMLOCK);
@@ -635,7 +639,13 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)

start = untagged_addr(start);

+ if (!len)
+ return 0;
+
len = PAGE_ALIGN(len + (offset_in_page(start)));
+ if (!len)
+ return -EINVAL;
+
start &= PAGE_MASK;

if (mmap_write_lock_killable(current->mm))
--
2.25.1
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