Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
New issues: - [Critical] Mismatch between `dmabuf->size` alignment check and `niov_shift` allocation causes zero-sized allocations and heap out-of-bounds writes. - [High] Arithmetic right shift of a negative `ssize_t` causes out-of-bounds array access for dmabuf chunks larger than 2GB. Pre-existing issues: - [High] Truncation of 64-bit `dma_addr_t` to 32-bit `unsigned long` corrupts chunk address tracking, causing memory leaks. -- --- Patch [1]: [PATCH net-next v7 1/3] net: devmem: allow rx-page-size > PAGE_SIZE per dmabuf binding --- commit 721bc7584b49aea3874dba5c8bcb4896d26b75ed Author: Bobby Eshleman <[email protected]> net: devmem: allow rx-page-size > PAGE_SIZE per dmabuf binding Every devmem dmabuf binding today hands the page_pool PAGE_SIZE niovs. This caps a single RX descriptor at PAGE_SIZE, burning CPU on buffer churn for large flows. Add a bind-time netlink attribute, NETDEV_A_DMABUF_RX_PAGE_SIZE, that lets userspace request a larger niov size. The value must be a power of two >= PAGE_SIZE. > diff --git a/net/core/devmem.c b/net/core/devmem.c > --- a/net/core/devmem.c > +++ b/net/core/devmem.c [ ... ] > @@ -93,13 +93,14 @@ net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding > *binding) > ssize_t offset; > ssize_t index; > > - dma_addr = gen_pool_alloc_owner(binding->chunk_pool, PAGE_SIZE, > + dma_addr = gen_pool_alloc_owner(binding->chunk_pool, > + 1UL << binding->niov_shift, > (void **)&owner); > if (!dma_addr) > return NULL; > > offset = dma_addr - owner->base_dma_addr; > - index = offset / PAGE_SIZE; > + index = offset >> binding->niov_shift; [Severity: High] Will this right shift perform an arithmetic shift when offset is negative? In net_devmem_alloc_dmabuf(), offset is declared as ssize_t (a 32-bit signed integer on 32-bit architectures). For a DMA chunk larger than 2GB, the difference between dma_addr and owner->base_dma_addr will overflow into a negative value. Previously, offset / PAGE_SIZE would implicitly promote offset to unsigned long because PAGE_SIZE is unsigned, yielding the correct positive index. By changing this to a right shift by binding->niov_shift, the result of the shift retains the signed type of the left operand (ssize_t). Right-shifting a negative signed value performs sign extension, resulting in a negative index. Could this lead to an out-of-bounds access on owner->area.niovs[index]? > niov = &owner->area.niovs[index]; > > niov->desc.pp_magic = 0; [ ... ] > @@ -113,12 +114,13 @@ void net_devmem_free_dmabuf(struct net_iov *niov) > { > struct net_devmem_dmabuf_binding *binding = > net_devmem_iov_binding(niov); > unsigned long dma_addr = net_devmem_get_dma_addr(niov); > + size_t niov_size = 1UL << binding->niov_shift; > > if (WARN_ON(!gen_pool_has_addr(binding->chunk_pool, dma_addr, > - PAGE_SIZE))) > + niov_size))) [Severity: High] This is a pre-existing issue, but can the 64-bit dma_addr be truncated here on 32-bit systems? In net_devmem_free_dmabuf(), the 64-bit return value from net_devmem_get_dma_addr() is assigned to an unsigned long dma_addr and passed to gen_pool_has_addr(). A similar truncation occurs in net_devmem_bind_dmabuf() where sg_dma_address(sg) is passed to the unsigned long virt parameter of gen_pool_add_owner(). On 32-bit systems with PAE/LPAE, dma_addr_t is 64-bit. If the original 64-bit address plus the chunk size crosses a 4GB boundary, the truncated 32-bit end_addr in gen_pool wraps around, breaking the bounds check in gen_pool_has_addr(). This causes the teardown path to trigger the WARN_ON and abort without freeing the chunk. Does this cause a permanent memory leak? > return; > > - gen_pool_free(binding->chunk_pool, dma_addr, PAGE_SIZE); > + gen_pool_free(binding->chunk_pool, dma_addr, niov_size); > } [ ... ] > @@ -248,18 +256,14 @@ net_devmem_bind_dmabuf(struct net_device *dev, void > *vdev, > goto err_unmap; > } > binding->tx_vec = kvmalloc_objs(struct net_iov *, > - dmabuf->size / PAGE_SIZE); > + dmabuf->size >> niov_shift); [Severity: Critical] Can tx_vec be allocated as a zero-sized array here? In net_devmem_bind_dmabuf(), the alignment check prior to this allocation still verifies that dmabuf->size is a multiple of PAGE_SIZE rather than niov_size: if (!IS_ALIGNED(dmabuf->size, PAGE_SIZE)) { err = -EINVAL; NL_SET_ERR_MSG(extack, "TX dma-buf size must be a multiple of PAGE_SIZE"); goto err_unmap; } If userspace binds a dmabuf where PAGE_SIZE <= dmabuf->size < niov_size (for example, 4K size with 64K niov_size), this check will pass, but the tx_vec allocation (dmabuf->size >> niov_shift) will allocate 0 elements. Later, if the exporter padded the scatterlist segment to niov_size, the scatterlist parsing loop computes owner->area.num_niovs = 1 and writes to tx_vec[0]. Could this result in a heap out-of-bounds write? > if (!binding->tx_vec) { > err = -ENOMEM; > goto err_unmap; > } > } -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
