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: Alexander Viro <v...@zeniv.linux.org.uk>
Cc: Christian Brauner <brau...@kernel.org>
Cc: Jan Kara <j...@suse.cz>
Cc: linux-fsde...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
fs/remap_range.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/remap_range.c b/fs/remap_range.c
index f8c1120b8311..15e91bf2c5e3 100644
--- a/fs/remap_range.c
+++ b/fs/remap_range.c
@@ -45,7 +45,7 @@ static int generic_remap_checks(struct file *file_in, loff_t
pos_in,
return -EINVAL;
/* Ensure offsets don't wrap. */
- if (pos_in + count < pos_in || pos_out + count < pos_out)
+ if (add_would_overflow(pos_in, count) || add_would_overflow(pos_out,
count))
return -EINVAL;
size_in = i_size_read(inode_in);
--
2.34.1
