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 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: Sumit Semwal <sumit.semwal@xxxxxxxxxx> Cc: Christian König <christian.koenig@xxxxxxx> Cc: "Christian König" <christian.koenig@xxxxxxx> Cc: linux-media@xxxxxxxxxxxxxxx Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- drivers/dma-buf/dma-buf.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 8fe5aa67b167..3743c63a9b59 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -1458,6 +1458,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF); int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma, unsigned long pgoff) { + unsigned long sum; + if (WARN_ON(!dmabuf || !vma)) return -EINVAL; @@ -1466,12 +1468,11 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma, return -EINVAL; /* check for offset overflow */ - if (pgoff + vma_pages(vma) < pgoff) + if (check_add_overflow(pgoff, vma_pages(vma), &sum)) return -EOVERFLOW; /* check for overflowing the buffer's size */ - if (pgoff + vma_pages(vma) > - dmabuf->size >> PAGE_SHIFT) + if (sum > dmabuf->size >> PAGE_SHIFT) return -EINVAL; /* readjust the vma */ -- 2.34.1
