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

[Wupeng Ma <mawupeng1@huawei.com>]

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