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: "Rafael J. Wysocki" <rafael@xxxxxxxxxx> Cc: Len Brown <lenb@xxxxxxxxxx> Cc: linux-acpi@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- drivers/acpi/custom_method.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c index d39a9b474727..0789317f4a1a 100644 --- a/drivers/acpi/custom_method.c +++ b/drivers/acpi/custom_method.c @@ -54,7 +54,7 @@ static ssize_t cm_write(struct file *file, const char __user *user_buf, if ((*ppos > max_size) || (*ppos + count > max_size) || - (*ppos + count < count) || + (add_would_overflow(count, *ppos)) || (count > uncopied_bytes)) { kfree(buf); buf = NULL; -- 2.34.1
