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Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , Bobby Eshleman , Pavel Begunkov , Ralf Lici Subject: Re: [PATCH net v1] net: devmem: prevent mixing fragments from different bindings Message-ID: References: <20261008033952.1399670-1-almasrymina@google.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20261008033952.1399670-1-almasrymina@google.com> On Thu, Oct 08, 2026 at 03:39:26AM +0000, Mina Almasry wrote: > validate_xmit_unreadable_skb() only inspects shinfo->frags[0] and > assumes all fragments in an unreadable skb belong to that same devmem > binding. However, tcp_sendmsg_locked() only checks that readability > matches the presence of a binding (skb_frags_readable(skb) != !binding), > allowing consecutive sendmsg() calls with different dmabuf bindings to > collapse into the same skb and bypass per-device and unbind checks in > validate_xmit_unreadable_skb(). > > Add net_devmem_skb_binding() to query the binding associated with an > skb, reuse it in validate_xmit_unreadable_skb(), and check in > zerocopy_fill_skb_from_devmem() that existing fragments match the target > binding. > > Fixes: bd61848900bff ("net: devmem: Implement TX path") > Cc: Pavel Begunkov > Cc: Stanislav Fomichev > Cc: Bobby Eshleman > Signed-off-by: Mina Almasry > --- > net/core/datagram.c | 2 +- > net/core/dev.c | 14 ++++---------- > net/core/devmem.h | 23 +++++++++++++++++++++++ > 3 files changed, 28 insertions(+), 11 deletions(-) > > diff --git a/net/core/datagram.c b/net/core/datagram.c > index 173b5d97bd409..ed8f1045f3cca 100644 > --- a/net/core/datagram.c > +++ b/net/core/datagram.c > @@ -712,7 +712,7 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from, > size_t virt_addr, size, off; > struct net_iov *niov; > > - if (i && skb_frags_readable(skb)) > + if (i && net_devmem_skb_binding(skb) != binding) > return -EFAULT; > > /* Devmem filling works by taking an IOVEC from the user where the > diff --git a/net/core/dev.c b/net/core/dev.c > index e76762e29360e..ad2b587dfee27 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -4054,8 +4054,7 @@ static struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb, > static struct sk_buff *validate_xmit_unreadable_skb(struct sk_buff *skb, > struct net_device *dev) > { > - struct skb_shared_info *shinfo; > - struct net_iov *niov; > + struct net_devmem_dmabuf_binding *binding; > > if (likely(skb_frags_readable(skb) || > dev->netmem_tx == NETMEM_TX_NO_DMA)) > @@ -4064,14 +4063,9 @@ static struct sk_buff *validate_xmit_unreadable_skb(struct sk_buff *skb, > if (dev->netmem_tx == NETMEM_TX_NONE) > goto out_free; > > - shinfo = skb_shinfo(skb); > - > - if (shinfo->nr_frags > 0) { > - niov = netmem_to_net_iov(skb_frag_netmem(&shinfo->frags[0])); > - if (net_is_devmem_iov(niov) && > - READ_ONCE(net_devmem_iov_binding(niov)->dev) != dev) > - goto out_free; > - } > + binding = net_devmem_skb_binding(skb); > + if (binding && READ_ONCE(binding->dev) != dev) > + goto out_free; > > out: > return skb; > diff --git a/net/core/devmem.h b/net/core/devmem.h > index 4a293a7d1149c..8c74037633ae8 100644 > --- a/net/core/devmem.h > +++ b/net/core/devmem.h > @@ -10,6 +10,7 @@ > #ifndef _NET_DEVMEM_H > #define _NET_DEVMEM_H > > +#include > #include > #include > > @@ -118,6 +119,22 @@ net_devmem_iov_binding(const struct net_iov *niov) > return net_devmem_iov_to_chunk_owner(niov)->binding; > } > > +static inline struct net_devmem_dmabuf_binding * > +net_devmem_skb_binding(const struct sk_buff *skb) > +{ > + const struct skb_shared_info *shinfo = skb_shinfo(skb); > + const struct net_iov *niov; > + > + if (skb_frags_readable(skb) || !shinfo->nr_frags) > + return NULL; > + > + niov = skb_frag_net_iov(&shinfo->frags[0]); > + if (!niov || !net_is_devmem_iov(niov)) > + return NULL; > + > + return net_devmem_iov_binding(niov); > +} > + > static inline u32 net_devmem_iov_binding_id(const struct net_iov *niov) > { > return net_devmem_iov_binding(niov)->id; > @@ -243,6 +260,12 @@ net_devmem_iov_binding(const struct net_iov *niov) > { > return NULL; > } > + > +static inline struct net_devmem_dmabuf_binding * > +net_devmem_skb_binding(const struct sk_buff *skb) > +{ > + return NULL; > +} > #endif > > #endif /* _NET_DEVMEM_H */ > > base-commit: 6d25ffca055a77787c21a36b66c253f76239411b > -- > 2.56.0.385.gd3acb90ef8-goog > Makes sense to me. Thanks. Reviewed-by: Bobby Eshleman