| Message ID | 20240123002814.1396804-13-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | overflow: Refactor open-coded arithmetic wrap-around | expand |
On Mon, Jan 22, 2024 at 04:26:48PM -0800, Kees Cook wrote: > In an effort to separate intentional arithmetic wrap-around from > unexpected wrap-around, we need to refactor places that depend on this > kind of math. One of the most common code patterns of this is: > > VAR + value < VAR > > Notably, this is considered "undefined behavior" for signed and pointer > types, which the kernel works around by using the -fno-strict-overflow > option in the build[1] (which used to just be -fwrapv). Regardless, we > want to get the kernel source to the position where we can meaningfully > instrument arithmetic wrap-around conditions and catch them when they > are unexpected, regardless of whether they are signed[2], unsigned[3], > or pointer[4] types. > > Refactor open-coded unsigned wrap-around addition test to use > check_add_overflow(), retaining the result for later usage (which removes > the redundant open-coded addition). This paves the way to enabling the > wrap-around sanitizer in the future. > > Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] > Link: https://github.com/KSPP/linux/issues/26 [2] > Link: https://github.com/KSPP/linux/issues/27 [3] > Link: https://github.com/KSPP/linux/issues/344 [4] > Cc: Chris Mason <clm@fb.com> > Cc: Josef Bacik <josef@toxicpanda.com> > Cc: David Sterba <dsterba@suse.com> > Cc: linux-btrfs@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c index b61099bf97a8..29a649507857 100644 --- a/fs/btrfs/extent_map.c +++ b/fs/btrfs/extent_map.c @@ -73,9 +73,11 @@ void free_extent_map(struct extent_map *em) /* Do the math around the end of an extent, handling wrapping. */ static u64 range_end(u64 start, u64 len) { - if (start + len < start) + u64 sum; + + if (check_add_overflow(start, len, &sum)) return (u64)-1; - return start + len; + return sum; } static int tree_insert(struct rb_root_cached *root, struct extent_map *em) diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h index e380fc08bbe4..3c4a6b977662 100644 --- a/fs/btrfs/extent_map.h +++ b/fs/btrfs/extent_map.h @@ -108,9 +108,11 @@ static inline int extent_map_in_tree(const struct extent_map *em) static inline u64 extent_map_end(const struct extent_map *em) { - if (em->start + em->len < em->start) + u64 sum; + + if (check_add_overflow(em->start, em->len, &sum)) return (u64)-1; - return em->start + em->len; + return sum; } void extent_map_tree_init(struct extent_map_tree *tree);
In an effort to separate intentional arithmetic wrap-around from unexpected wrap-around, we need to refactor places that depend on this kind of math. One of the most common code patterns of this is: VAR + value < VAR Notably, this is considered "undefined behavior" for signed and pointer types, which the kernel works around by using the -fno-strict-overflow option in the build[1] (which used to just be -fwrapv). Regardless, we want to get the kernel source to the position where we can meaningfully instrument arithmetic wrap-around conditions and catch them when they are unexpected, regardless of whether they are signed[2], unsigned[3], or pointer[4] types. Refactor open-coded unsigned wrap-around addition test to use check_add_overflow(), retaining the result for later usage (which removes the redundant open-coded addition). This paves the way to enabling the wrap-around sanitizer in the future. Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] Link: https://github.com/KSPP/linux/issues/26 [2] Link: https://github.com/KSPP/linux/issues/27 [3] Link: https://github.com/KSPP/linux/issues/344 [4] Cc: Chris Mason <clm@fb.com> Cc: Josef Bacik <josef@toxicpanda.com> Cc: David Sterba <dsterba@suse.com> Cc: linux-btrfs@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- fs/btrfs/extent_map.c | 6 ++++-- fs/btrfs/extent_map.h | 6 ++++-- 2 files changed, 8 insertions(+), 4 deletions(-)