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 unsigned wrap-around sanitizer[2] 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: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Uladzislau Rezki <urezki@xxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx> Cc: linux-mm@xxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- mm/vmalloc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index d12a17fc0c17..7932ac99e9d3 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1223,6 +1223,7 @@ is_within_this_va(struct vmap_area *va, unsigned long size, unsigned long align, unsigned long vstart) { unsigned long nva_start_addr; + unsigned long sum; if (va->va_start > vstart) nva_start_addr = ALIGN(va->va_start, align); @@ -1230,11 +1231,11 @@ is_within_this_va(struct vmap_area *va, unsigned long size, nva_start_addr = ALIGN(vstart, align); /* Can be overflowed due to big size or alignment. */ - if (nva_start_addr + size < nva_start_addr || + if (check_add_overflow(nva_start_addr, size, &sum) || nva_start_addr < vstart) return false; - return (nva_start_addr + size <= va->va_end); + return (sum <= va->va_end); } /* -- 2.34.1
