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mseal: fix is_madv_discard()

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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
Fixes: 8be7258aad ("mseal: add mseal syscall")
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
Tested-by: Jeff Xu <jeffxu@chromium.org>
Reviewed-by: Jeff Xu <jeffxu@chromium.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Pedro Falcato 2024-08-07 18:33:35 +01:00 • committed by Andrew Morton
parent 7c626ce4ba
commit e46bc2e7eb
1 changed files with 11 additions and 3 deletions
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14
mm/mseal.c
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@ -40,9 +40,17 @@ static bool can_modify_vma(struct vm_area_struct *vma)
static bool is_madv_discard(int behavior) static bool is_madv_discard(int behavior)
{ {
return behavior & switch (behavior) {
(MADV_FREE | MADV_DONTNEED | MADV_DONTNEED_LOCKED | case MADV_FREE:
MADV_REMOVE | MADV_DONTFORK | MADV_WIPEONFORK); 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) static bool is_ro_anon(struct vm_area_struct *vma)