Commit e46bc2e7 authored by Pedro Falcato's avatar Pedro Falcato Committed by Andrew Morton
Browse files

mseal: fix is_madv_discard() 

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: 8be7258a ("mseal: add mseal syscall")
Signed-off-by: default avatarPedro Falcato <pedro.falcato@gmail.com>
Tested-by: default avatarJeff Xu <jeffxu@chromium.org>
Reviewed-by: default avatarJeff 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7c626ce4

mm/mseal.c

+11 −3
Original line number Diff line number Diff line
@@ -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)