From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 68A99224CA; Mon, 25 Sep 2023 18:27:36 +0000 (UTC) Received: from mail-ot1-x336.google.com (mail-ot1-x336.google.com [IPv6:2607:f8b0:4864:20::336]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BFAD295; Mon, 25 Sep 2023 11:27:34 -0700 (PDT) Received: by mail-ot1-x336.google.com with SMTP id 46e09a7af769-6bf58009a8dso4353746a34.1; Mon, 25 Sep 2023 11:27:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1695666454; x=1696271254; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=hORITzYCrCj4rLhQhCGh606G9+/re5bZyItzl2r+Jjw=; b=B7qjSkIKyyjJgclQzFXrmqEp6H0IPyBDdviQo6W1qNfYtSXEtvogQWA6gUrNODQVyu 0sYiaE26+sRJV8Z5/f/sTn85M29bx9BKZtHC1yqHhaPufhqRRbooadOIJHLw/UhBQBKL 6BgnNm0Eui595fS+a7/pUgjuOCtDXYdGDepA5w/B2u98TOzpEnSi6ODx66uSpZZLZS72 SrVXalvvbZoF1jZy/M8wZ1C96S7fDeYCCqYCEFU1jDoFJqw/Mn0StnoKMbEsWN59vmy2 1DzdEuVCBRZG+5dLC9JLR2+xv9jXGoaD9uRmodA0CTs/FNcjmOOilQq2SWHpD4vYiwNl g7eQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695666454; x=1696271254; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=hORITzYCrCj4rLhQhCGh606G9+/re5bZyItzl2r+Jjw=; b=TKq373NEbJdaQtwxAs25rEzi6n2qIL4YL5oAb9C+XHOTY8+0rgQg5adZIBurDy2f7x gHTm+hnyPKh3HMNo3zWGKBYwsGV44GG3pzSRsbI/2dUKtDZ2Im3cIGAruSGezIJ8nITm iL9qyrmIHhlyvx2dzQ071InKFLgGYkHtoerqUy/ZXZ0UCzYjAHOiPa7XjNxAkrzhEFvj /MqYNnmRasUePCM/PdV/uMxciNDndDD9jSeT0HuF/n+AIk0BQB4JAB1H4bRTy9NshEZt 1eoOXzoLFBozC2wQO1ZFBJXcnBHVtH5bhIxa/jlP2MnwsAHWKsKQLAVKAkqBq0UQ7/E1 5YAA== X-Gm-Message-State: AOJu0YyMw6n9KWAbc31S3EcplhCDrECRwJ0NllQm4ArCMxmTKLby0x3p 7AS6jO74XkoRMXuuiBbX/mRkKNOc8Ls= X-Google-Smtp-Source: AGHT+IETQ+D4lE/eOVkhNhtvqvSBiHvKSq2Yx+ZFEpXDng3OTbYWEMx9xVDZhp3XYlfyl+BYhjdihA== X-Received: by 2002:a05:6830:2004:b0:6bd:63b:4b21 with SMTP id e4-20020a056830200400b006bd063b4b21mr7799078otp.15.1695666454009; Mon, 25 Sep 2023 11:27:34 -0700 (PDT) Received: from localhost ([2605:59c8:148:ba00:51e:699c:e63:c15a]) by smtp.gmail.com with ESMTPSA id g1-20020a62e301000000b0068bbd43a6e2sm8632708pfh.10.2023.09.25.11.27.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Sep 2023 11:27:33 -0700 (PDT) Date: Mon, 25 Sep 2023 11:27:32 -0700 From: John Fastabend To: Jakub Sitnicki , bpf@vger.kernel.org Cc: netdev@vger.kernel.org, kernel-team@cloudflare.com, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , John Fastabend , Cong Wang Message-ID: <6511d1143dc59_110e52088a@john.notmuch> In-Reply-To: <20230920102055.42662-1-jakub@cloudflare.com> References: <20230920102055.42662-1-jakub@cloudflare.com> Subject: RE: [PATCH bpf] bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Jakub Sitnicki wrote: > With a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages > sent from one TCP socket (s1) to actually egress from another TCP > socket (s2): > > tcp_bpf_sendmsg(s1) // = sk_prot->sendmsg > tcp_bpf_send_verdict(s1) // __SK_REDIRECT case > tcp_bpf_sendmsg_redir(s2) > tcp_bpf_push_locked(s2) > tcp_bpf_push(s2) > tcp_rate_check_app_limited(s2) // expects tcp_sock > tcp_sendmsg_locked(s2) // ditto > > There is a hard-coded assumption in the call-chain, that the egress > socket (s2) is a TCP socket. > > However in commit 122e6c79efe1 ("sock_map: Update sock type checks for > UDP") we have enabled redirects to non-TCP sockets. This was done for the > sake of BPF sk_skb programs. There was no indention to support sk_msg > send-to-egress use case. > > As a result, attempts to send-to-egress through a non-TCP socket lead to a > crash due to invalid downcast from sock to tcp_sock: > > BUG: kernel NULL pointer dereference, address: 000000000000002f > ... > Call Trace: > > ? show_regs+0x60/0x70 > ? __die+0x1f/0x70 > ? page_fault_oops+0x80/0x160 > ? do_user_addr_fault+0x2d7/0x800 > ? rcu_is_watching+0x11/0x50 > ? exc_page_fault+0x70/0x1c0 > ? asm_exc_page_fault+0x27/0x30 > ? tcp_tso_segs+0x14/0xa0 > tcp_write_xmit+0x67/0xce0 > __tcp_push_pending_frames+0x32/0xf0 > tcp_push+0x107/0x140 > tcp_sendmsg_locked+0x99f/0xbb0 > tcp_bpf_push+0x19d/0x3a0 > tcp_bpf_sendmsg_redir+0x55/0xd0 > tcp_bpf_send_verdict+0x407/0x550 > tcp_bpf_sendmsg+0x1a1/0x390 > inet_sendmsg+0x6a/0x70 > sock_sendmsg+0x9d/0xc0 > ? sockfd_lookup_light+0x12/0x80 > __sys_sendto+0x10e/0x160 > ? syscall_enter_from_user_mode+0x20/0x60 > ? __this_cpu_preempt_check+0x13/0x20 > ? lockdep_hardirqs_on+0x82/0x110 > __x64_sys_sendto+0x1f/0x30 > do_syscall_64+0x38/0x90 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Reject selecting a non-TCP sockets as redirect target from a BPF sk_msg > program to prevent the crash. When attempted, user will receive an EACCES > error from send/sendto/sendmsg() syscall. > > Fixes: 122e6c79efe1 ("sock_map: Update sock type checks for UDP") > Signed-off-by: Jakub Sitnicki > --- > FYI, I'm working on revamping the sockmap_listen selftest, which exercises > some of redirect combinations, to cover the whole combination matrix so > that we can catch these kinds of problems early on. Yes this would be appreciated. > > net/core/sock_map.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index cb11750b1df5..4292c2ed1828 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -668,6 +668,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg, > sk = __sock_map_lookup_elem(map, key); > if (unlikely(!sk || !sock_map_redirect_allowed(sk))) > return SK_DROP; > + if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk)) > + return SK_DROP; > > msg->flags = flags; > msg->sk_redir = sk; > @@ -1267,6 +1269,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg, > sk = __sock_hash_lookup_elem(map, key); > if (unlikely(!sk || !sock_map_redirect_allowed(sk))) > return SK_DROP; > + if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk)) > + return SK_DROP; As a stop gap I think this is fine. If anyone wants to add support though I do think as a use case it would make sense to redirect TCP into an AF_UNIX socket and vice versa. Acked-by: John Fastabend