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 wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers 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 <c...@fb.com>
Cc: Josef Bacik <jo...@toxicpanda.com>
Cc: David Sterba <dste...@suse.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
fs/btrfs/ordered-data.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 59850dc17b22..2e0865693cee 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -813,7 +813,7 @@ int btrfs_wait_ordered_range(struct inode *inode, u64
start, u64 len)
u64 orig_end;
struct btrfs_ordered_extent *ordered;
- if (start + len < start) {
+ if (add_would_overflow(start, len)) {
orig_end = OFFSET_MAX;
} else {
orig_end = start + len - 1;
--
2.34.1
