[PATCH v4 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.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
---
 mm/mlock.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/mlock.c b/mm/mlock.c
index 617469fce96d..eb68476da497 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -568,6 +568,7 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
 	unsigned long locked;
 	unsigned long lock_limit;
 	int error = -ENOMEM;
+	size_t old_len = len;
 
 	start = untagged_addr(start);
 
@@ -577,6 +578,9 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
 	len = PAGE_ALIGN(len + (offset_in_page(start)));
 	start &= PAGE_MASK;
 
+	if (old_len != 0 && len == 0)
+		return -EINVAL;
+
 	lock_limit = rlimit(RLIMIT_MEMLOCK);
 	lock_limit >>= PAGE_SHIFT;
 	locked = len >> PAGE_SHIFT;
@@ -631,12 +635,16 @@ SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 {
 	int ret;
+	size_t old_len = len;
 
 	start = untagged_addr(start);
 
 	len = PAGE_ALIGN(len + (offset_in_page(start)));
 	start &= PAGE_MASK;
 
+	if (old_len != 0 && len == 0)
+		return -EINVAL;
+
 	if (mmap_write_lock_killable(current->mm))
 		return -EINTR;
 	ret = apply_vma_lock_flags(start, len, 0);
-- 
2.25.1