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Mon, 26 Aug 2024 18:39:12 -0700 (PDT) Received: from n191-036-066.byted.org ([147.160.184.150]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-454fe1c5711sm48263401cf.82.2024.08.26.18.39.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Aug 2024 18:39:11 -0700 (PDT) From: zijianzhang@bytedance.com To: bpf@vger.kernel.org Cc: edumazet@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, dsahern@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, shuah@kernel.org, xiyou.wangcong@gmail.com, wangdongdong.6@bytedance.com, zhoufeng.zf@bytedance.com, Amery Hung , Zijian Zhang Subject: [PATCH bpf-next v2 1/2] bpf: tcp: prevent bpf_reserve_hdr_opt() from growing skb larger than MTU Date: Tue, 27 Aug 2024 01:37:35 +0000 Message-Id: <20240827013736.2845596-2-zijianzhang@bytedance.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20240827013736.2845596-1-zijianzhang@bytedance.com> References: <20240827013736.2845596-1-zijianzhang@bytedance.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net From: Amery Hung This series prevents sockops users from accidentally causing packet drops. This can happen when a BPF_SOCK_OPS_HDR_OPT_LEN_CB program reserves different option lengths in tcp_sendmsg(). Initially, sockops BPF_SOCK_OPS_HDR_OPT_LEN_CB program will be called to reserve a space in tcp_send_mss(), which will return the MSS for TSO. Then, BPF_SOCK_OPS_HDR_OPT_LEN_CB will be called in __tcp_transmit_skb() again to calculate the actual tcp_option_size and skb_push() the total header size. skb->gso_size is restored from TCP_SKB_CB(skb)->tcp_gso_size, which is derived from tcp_send_mss() where we first call HDR_OPT_LEN. If the reserved opt size is smaller than the actual header size, the len of the skb can exceed the MTU. As a result, ip(6)_fragment will drop the packet if skb->ignore_df is not set. To prevent this accidental packet drop, we need to make sure the second call to the BPF_SOCK_OPS_HDR_OPT_LEN_CB program reserves space not more than the first time. Since this cannot be done during verification time, we add a runtime sanity check to have bpf_reserve_hdr_opt return an error instead of causing packet drops later. Signed-off-by: Amery Hung Co-developed-by: Zijian Zhang Signed-off-by: Zijian Zhang --- include/net/tcp.h | 8 ++++++++ net/ipv4/tcp_input.c | 8 -------- net/ipv4/tcp_output.c | 13 +++++++++++-- 3 files changed, 19 insertions(+), 10 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 2aac11e7e1cc..e202eeb19be4 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1058,6 +1058,14 @@ static inline int tcp_skb_mss(const struct sk_buff *skb) return TCP_SKB_CB(skb)->tcp_gso_size; } +/* I wish gso_size would have a bit more sane initialization than + * something-or-zero which complicates things + */ +static inline int tcp_skb_seglen(const struct sk_buff *skb) +{ + return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); +} + static inline bool tcp_skb_can_collapse_to(const struct sk_buff *skb) { return likely(!TCP_SKB_CB(skb)->eor); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index e37488d3453f..c1ffe19b0717 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1550,14 +1550,6 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, return true; } -/* I wish gso_size would have a bit more sane initialization than - * something-or-zero which complicates things - */ -static int tcp_skb_seglen(const struct sk_buff *skb) -{ - return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); -} - /* Shifting pages past head area doesn't work */ static int skb_can_shift(const struct sk_buff *skb) { diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 16c48df8df4c..f5996cdbb2ba 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1033,10 +1033,19 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb if (unlikely(BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG))) { unsigned int remaining = MAX_TCP_OPTION_SPACE - size; + unsigned int old_remaining; - bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining); + if (skb) { + unsigned int reserved_opt_spc; + + reserved_opt_spc = tp->mss_cache - tcp_skb_seglen(skb); + if (reserved_opt_spc < remaining) + remaining = reserved_opt_spc; + } - size = MAX_TCP_OPTION_SPACE - remaining; + old_remaining = remaining; + bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining); + size += old_remaining - remaining; } return size;