[PATCH 4/4] mseal: fix is_madv_discard()
jeffxu at chromium.org
jeffxu at chromium.org
Wed Nov 27 20:29:02 UTC 2024
From: Pedro Falcato <pedro.falcato at gmail.com>
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.
As a result the kernel could erroneously block certain madvises (e.g
MADV_RANDOM or MADV_HUGEPAGE) on sealed VMAs due to them sharing bits
with blocked MADV operations (e.g REMOVE or WIPEONFORK).
This is obviously incorrect, so use a switch statement instead.
Link: https://lkml.kernel.org/r/20240807173336.2523757-1-pedro.falcato@gmail.com
Link: https://lkml.kernel.org/r/20240807173336.2523757-2-pedro.falcato@gmail.com
Signed-off-by: Pedro Falcato <pedro.falcato at gmail.com>
Tested-by: Jeff Xu <jeffxu at chromium.org>
Reviewed-by: Jeff Xu <jeffxu at chromium.org>
Cc: Kees Cook <kees at kernel.org>
Cc: Liam R. Howlett <Liam.Howlett at oracle.com>
Cc: Shuah Khan <shuah at kernel.org>
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
(cherry picked from commit e46bc2e7eb90a370bc27fa2fd98cb8251e7da1ec)
Signed-off-by: Jeff Xu <jeffxu at chromium.org>
---
mm/mseal.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/mm/mseal.c b/mm/mseal.c
index bf783bba8ed0..15bba28acc00 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)
--
2.47.0.338.g60cca15819-goog
More information about the kernel-team
mailing list