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[67.230.185.89]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33ba4f55735sm11779694eec.24.2026.09.11.22.53.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Sep 2026 22:53:35 -0700 (PDT) From: Gris Ge To: David Ahern , Ido Schimmel , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Cosmin Ratiu , Gal Pressman , Kees Cook , Tariq Toukan , netdev@vger.kernel.org (open list:NETWORKING [IPv4/IPv6]), linux-kernel@vger.kernel.org (open list) Cc: Gris Ge , stable@vger.kernel.org Subject: [PATCH] net: ip_tunnel: initialize `options_len` before referencing options Date: Sat, 12 Sep 2026 13:53:03 +0800 Message-ID: <20260912055304.1415016-1-cnfourt@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The following command triggers a kernel panic: ip link add d0 type dummy; ip link set d0 up ip route add 10.30.0.0/16 \ encap ip id 300 geneve_opts 4660:66:11223344 dev d0 memcpy: detected buffer overflow: 4 byte write of buffer size 0 kernel BUG at lib/string_helpers.c:1044! ... ip_tun_parse_opts.part.0.cold+0x10/0x10 ip_tun_build_state+0x116/0x2a0 On kernels built with GCC 15+ and `CONFIG_FORTIFY_SOURCE`, the fortified `memcpy()` got 0 sized destination with request of 4 bytes length: static int ip_tun_parse_opts_geneve(...) { ... attr = tb[LWTUNNEL_IP_OPT_GENEVE_DATA]; data_len = nla_len(attr); /* == 4 */ struct geneve_opt *opt = ip_tunnel_info_opts(info) + opts_len; memcpy(opt->opt_data, nla_data(attr), data_len); /* ^^^^^^^^^^^^^ 0 since options_len is assigned afterwards */ Fixed by initializing the counter before the options are referenced matching what `ip_tunnel_info_opts_set()` already does Fixes: bb5e62f2d547 ("net: Add options as a flexible array to struct ip_tunnel_info") Cc: stable@vger.kernel.org Signed-off-by: Gris Ge --- net/ipv4/ip_tunnel_core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c index 5168d546ea2f..8fb4742aca92 100644 --- a/net/ipv4/ip_tunnel_core.c +++ b/net/ipv4/ip_tunnel_core.c @@ -711,6 +711,7 @@ static int ip_tun_build_state(struct net *net, struct nlattr *attr, new_state->type = LWTUNNEL_ENCAP_IP; tun_info = lwt_tun_info(new_state); + tun_info->options_len = opt_len; err = ip_tun_set_opts(tb[LWTUNNEL_IP_OPTS], tun_info, extack); if (err < 0) { @@ -753,7 +754,6 @@ static int ip_tun_build_state(struct net *net, struct nlattr *attr, } tun_info->mode = IP_TUNNEL_INFO_TX; - tun_info->options_len = opt_len; *ts = new_state; @@ -1005,6 +1005,7 @@ static int ip6_tun_build_state(struct net *net, struct nlattr *attr, new_state->type = LWTUNNEL_ENCAP_IP6; tun_info = lwt_tun_info(new_state); + tun_info->options_len = opt_len; err = ip_tun_set_opts(tb[LWTUNNEL_IP6_OPTS], tun_info, extack); if (err < 0) { @@ -1040,7 +1041,6 @@ static int ip6_tun_build_state(struct net *net, struct nlattr *attr, } tun_info->mode = IP_TUNNEL_INFO_TX | IP_TUNNEL_INFO_IPV6; - tun_info->options_len = opt_len; *ts = new_state; -- 2.55.0