[PATCH 1/2] mseal: Fix is_madv_discard()

[Pedro Falcato]

is_madv_discard did its check wrong. MADV_ flags are not bitwise,
they're normal sequential numbers. So, for instance:
	behavior & (/* ... */ | MADV_REMOVE)

tagged both MADV_REMOVE and MADV_RANDOM (bit 0 set) as
discard operations. This is obviously incorrect, so use
a switch statement instead.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 8be7258aad44 ("mseal: add mseal syscall")
Signed-off-by: Pedro Falcato <pedro.falcato@xxxxxxxxx>
---
 mm/mseal.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/mseal.c b/mm/mseal.c
index bf783bba8ed..15bba28acc0 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -40,9 +40,17 @@ static bool can_modify_vma(struct vm_area_struct *vma)
 
 static bool is_madv_discard(int behavior)
 {
-	return	behavior &
-		(MADV_FREE | MADV_DONTNEED | MADV_DONTNEED_LOCKED |
-		 MADV_REMOVE | MADV_DONTFORK | MADV_WIPEONFORK);
+	switch (behavior) {
+	case MADV_FREE:
+	case MADV_DONTNEED:
+	case MADV_DONTNEED_LOCKED:
+	case MADV_REMOVE:
+	case MADV_DONTFORK:
+	case MADV_WIPEONFORK:
+		return true;
+	}
+
+	return false;
 }
 
 static bool is_ro_anon(struct vm_area_struct *vma)
-- 
2.46.0