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Tue, 19 May 2026 14:07:47 -0700 (PDT) Received: from devvm29614.prn0.facebook.com ([2a03:2880:f814:1e::]) by smtp.gmail.com with ESMTPSA id af79cd13be357-910bc83bbf5sm1964749085a.28.2026.05.19.14.07.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 14:07:47 -0700 (PDT) Date: Tue, 19 May 2026 14:07:43 -0700 From: Bobby Eshleman To: David Carlier Cc: netdev@vger.kernel.org, stable@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, sdf@fomichev.me, sdf.kernel@gmail.com, kaiyuanz@google.com, almasrymina@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH net v2] net: devmem: reject dma-buf bind with non-page-aligned size or SG length Message-ID: References: <20260519203530.66310-1-devnexen@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260519203530.66310-1-devnexen@gmail.com> On Tue, May 19, 2026 at 09:35:30PM +0100, David Carlier wrote: > net_devmem_bind_dmabuf() trusts dmabuf->size and sg_dma_len() to be > PAGE_SIZE multiples without checking: > > - tx_vec is sized dmabuf->size / PAGE_SIZE, and > net_devmem_get_niov_at() only bounds-checks virt_addr < dmabuf->size > before indexing tx_vec[virt_addr / PAGE_SIZE]. With size = > N*PAGE_SIZE + r (1 <= r < PAGE_SIZE), sendmsg() at iov_base = > N*PAGE_SIZE passes the bound check and reads tx_vec[N] -- one past. > > - owner->area.num_niovs = len / PAGE_SIZE while gen_pool_add_owner() > covers the full byte len, so a non-page-multiple non-final sg > desyncs num_niovs from the gen_pool region for every later sg, on > both RX and TX. > > dma-buf does not require page-aligned sizes, so the bind path has to > enforce what its own indexing assumes. Reject both with -EINVAL. > > The size check is TX-only (only tx_vec is sized off dmabuf->size); the > SG-length check covers both directions. > > Fixes: bd61848900bf ("net: devmem: Implement TX path") > Cc: stable@vger.kernel.org > Signed-off-by: David Carlier > --- > Changes in v2: > - Reframe commit message around the kernel-side OOB instead of > "real exporters already page-align", which read as the OOB being > unreachable and undercut Cc: stable (Stanislav Fomichev). > - Hoist the SG-length check out of the if (TX) branch so it covers > RX too; RX has the same num_niovs / gen_pool desync on a > contract-violating exporter, just without an OOB. Keep the > size-multiple check TX-only (Stanislav Fomichev). > - Drop bool todevice; compare direction == DMA_TO_DEVICE inline to > match the existing call site at the tx_vec[] assignment > (Bobby Eshleman). > > net/core/devmem.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/net/core/devmem.c b/net/core/devmem.c > index 468344739db2..4f71de44c0fb 100644 > --- a/net/core/devmem.c > +++ b/net/core/devmem.c > @@ -241,6 +241,11 @@ net_devmem_bind_dmabuf(struct net_device *dev, > } > > if (direction == DMA_TO_DEVICE) { > + 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; > + } > binding->tx_vec = kvmalloc_objs(struct net_iov *, > dmabuf->size / PAGE_SIZE); > if (!binding->tx_vec) { > @@ -267,6 +272,12 @@ net_devmem_bind_dmabuf(struct net_device *dev, > size_t len = sg_dma_len(sg); > struct net_iov *niov; > > + if (!IS_ALIGNED(len, PAGE_SIZE)) { > + err = -EINVAL; > + NL_SET_ERR_MSG(extack, "dma-buf SG length must be PAGE_SIZE aligned"); > + goto err_free_chunks; > + } > + > owner = kzalloc_node(sizeof(*owner), GFP_KERNEL, > dev_to_node(&dev->dev)); > if (!owner) { > -- > 2.53.0 LGTM. Reviewed-by: Bobby Eshleman