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: Mikulas Patocka <miku...@artax.karlin.mff.cuni.cz>
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
fs/hpfs/alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/hpfs/alloc.c b/fs/hpfs/alloc.c
index 66617b1557c6..e9c7cc6033b5 100644
--- a/fs/hpfs/alloc.c
+++ b/fs/hpfs/alloc.c
@@ -99,7 +99,7 @@ static int chk_if_allocated(struct super_block *s, secno sec,
char *msg)
int hpfs_chk_sectors(struct super_block *s, secno start, int len, char *msg)
{
- if (start + len < start || start < 0x12 ||
+ if (add_would_overflow(start, len) || start < 0x12 ||
start + len > hpfs_sb(s)->sb_fs_size) {
hpfs_error(s, "sector(s) '%s' badly placed at %08x", msg,
start);
return 1;
--
2.34.1
