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Fri, 11 Sep 2026 10:23:59 -0700 (PDT) From: Shihuang Liu To: netdev@vger.kernel.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, john.fastabend@gmail.com, sdf@fomichev.me, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, akpm@linux-foundation.org, leon.hwang@linux.dev, yatsenko@meta.com, kpsingh@kernel.org, dmitry.baryshkov@oss.qualcomm.com, jordan@jrife.io, nhudson@akamai.com, avinash.duduskar@gmail.com, rongtao@cestc.cn, joe@wand.net.nz, Shihuang Liu Subject: [PATCH bpf v2 2/2] bpf: revalidate assigned sockets after protocol change Date: Sat, 12 Sep 2026 01:23:13 +0800 Message-ID: <20260911172313.64009-2-shlomojune6@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260911172313.64009-1-shlomojune6@gmail.com> References: <20260911172313.64009-1-shlomojune6@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit An IPv4 packet can be assigned to an AF_INET socket and then translated to IPv6 by bpf_skb_change_proto(). Since the translation preserves the socket assignment, the IPv6 packet can still be delivered to the IPv4 socket, bypassing the family check in bpf_sk_assign(). After a successful protocol change, recheck any prefetched socket against the new protocol and call skb_orphan() if its address family is incompatible. This releases the assignment through the existing skb destructor, allowing normal socket lookup or a new assignment by the BPF program. Fixes: cf7fbe660f2d ("bpf: Add socket assign support") Assisted-by: LLM Signed-off-by: Shihuang Liu --- Changes since v1: - Revalidate prefetched sockets after bpf_skb_change_proto() changes the packet protocol, closing a bypass of assignment-time validation. - Preserve compatible dual-stack assignments and release incompatible assignments through their existing skb destructor. - Split the fix into two patches and target the BPF fixes tree. v1: https://lore.kernel.org/netdev/20260823101809.26802-1-shlomojune6@gmail.com/ include/uapi/linux/bpf.h | 4 ++++ net/core/filter.c | 5 +++++ tools/include/uapi/linux/bpf.h | 4 ++++ 3 files changed, 13 insertions(+) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 5d8f5e2c8db38..0de7967077a2e 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -2659,6 +2659,10 @@ union bpf_attr { * checked and segments are recalculated by the GSO/GRO engine. * The size for GSO target is adapted as well. * + * On success, an assigned socket is released if its address + * family is incompatible with the new protocol. Assign a + * compatible socket after translation if required. + * * All values for *flags* are reserved for future usage, and must * be left at zero. * diff --git a/net/core/filter.c b/net/core/filter.c index e9cc76b775c0c..79a0e484d9dd4 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -3547,6 +3547,11 @@ BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto, if (ret) return ret; + /* Protocol translation can invalidate an earlier socket assignment. */ + if (skb_sk_is_prefetched(skb) && + !bpf_sk_assign_family_ok(skb, skb->sk)) + skb_orphan(skb); + if (skb_valid_dst(skb)) skb_dst_drop(skb); diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 5d8f5e2c8db38..0de7967077a2e 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -2659,6 +2659,10 @@ union bpf_attr { * checked and segments are recalculated by the GSO/GRO engine. * The size for GSO target is adapted as well. * + * On success, an assigned socket is released if its address + * family is incompatible with the new protocol. Assign a + * compatible socket after translation if required. + * * All values for *flags* are reserved for future usage, and must * be left at zero. * -- 2.43.0