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[204.195.112.43]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b0fc1bc1e6sm5641735a91.0.2026.11.08.17.44.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Nov 2026 17:44:39 -0800 (PST) From: Stephen Hemminger To: netdev@vger.kernel.org Cc: dsahern@kernel.org, Stephen Hemminger Subject: [PATCH iproute2 2/5] netlink: ignore messages not sent by the kernel Date: Sun, 8 Nov 2026 17:43:59 -0800 Message-ID: <20261109014434.115922-3-stephen@networkplumber.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109014434.115922-1-stephen@networkplumber.org> References: <20261109014434.115922-1-stephen@networkplumber.org> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A process with CAP_NET_ADMIN over the namespace can send unicast or multicast netlink datagrams to iproute2 tools. rtnl_listen() and mnlu_socket_recv_run() never checked the sender, so monitors print forged events and exit or overflow on malformed ones. The dump and talk loops checked nl_pid only after framing checks and after ss -D had recorded the datagram. Drop any datagram whose sender is not port id 0 right after recvmsg(), in rtnl_recvmsg(), rtnl_listen() and a new mnlu_socket_recvfrom(). Reported-by: Anthropic OSS scanner (ANT-2026-ISEFARJF) Reported-by: Anthropic OSS scanner (ANT-2026-GYQAKSVI) Assisted-by: Claude:claude-opus-5-5 Signed-off-by: Stephen Hemminger --- include/mnl_utils.h | 1 + lib/libnetlink.c | 36 ++++++++++++++++++++---------------- lib/mnl_utils.c | 35 ++++++++++++++++++++++++++++++++++- rdma/stat.c | 2 +- 4 files changed, 56 insertions(+), 18 deletions(-) diff --git a/include/mnl_utils.h b/include/mnl_utils.h index d809383c..19a49de6 100644 --- a/include/mnl_utils.h +++ b/include/mnl_utils.h @@ -28,6 +28,7 @@ int mnl_add_nl_group(struct mnl_socket *nl, unsigned int group); uint32_t mnlu_next_seq(void); struct nlmsghdr *mnlu_msg_prepare(void *buf, uint32_t nlmsg_type, uint16_t flags, void *extra_header, size_t extra_header_size); +ssize_t mnlu_socket_recvfrom(const struct mnl_socket *nl, void *buf, size_t buf_size); int mnlu_socket_recv_run(struct mnl_socket *nl, unsigned int seq, void *buf, size_t buf_size, mnl_cb_t cb, void *data); int mnlu_gen_socket_recv_run(struct mnlu_gen_socket *nlg, mnl_cb_t cb, diff --git a/lib/libnetlink.c b/lib/libnetlink.c index 6ff9cace..b923ba02 100644 --- a/lib/libnetlink.c +++ b/lib/libnetlink.c @@ -843,12 +843,22 @@ static int __rtnl_recvmsg(int fd, struct msghdr *msg, int flags) return len; } +/* Netlink datagrams from other processes are discarded */ +static bool rtnl_from_kernel(const struct msghdr *msg) +{ + const struct sockaddr_nl *nladdr = msg->msg_name; + + return msg->msg_namelen == sizeof(*nladdr) && nladdr->nl_pid == 0; +} + static int rtnl_recvmsg(int fd, struct msghdr *msg, char **answer) { struct iovec *iov = msg->msg_iov; char *buf; int len; +again: + msg->msg_namelen = sizeof(struct sockaddr_nl); iov->iov_base = NULL; iov->iov_len = 0; @@ -873,6 +883,11 @@ static int rtnl_recvmsg(int fd, struct msghdr *msg, char **answer) return len; } + if (!rtnl_from_kernel(msg)) { + free(buf); + goto again; + } + if (answer) *answer = buf; else @@ -918,8 +933,7 @@ static int rtnl_dump_filter_l(struct rtnl_handle *rth, h->nlmsg_flags &= ~a->nc_flags; - if (nladdr.nl_pid != 0 || - h->nlmsg_pid != rth->local.nl_pid || + if (h->nlmsg_pid != rth->local.nl_pid || h->nlmsg_seq != rth->dump) goto skip_it; @@ -1066,12 +1080,6 @@ next: if (status < 0) return status; - if (msg.msg_namelen != sizeof(nladdr)) { - fprintf(stderr, - "sender address length == %d\n", - msg.msg_namelen); - exit(1); - } for (h = (struct nlmsghdr *)buf; status >= sizeof(*h); ) { int len = h->nlmsg_len; int l = len - sizeof(*h); @@ -1088,8 +1096,7 @@ next: exit(1); } - if (nladdr.nl_pid != 0 || - h->nlmsg_pid != rtnl->local.nl_pid || + if (h->nlmsg_pid != rtnl->local.nl_pid || (unsigned int)(seq - h->nlmsg_seq) >= iovlen) { /* Don't forget to skip that message. */ status -= NLMSG_ALIGN(len); @@ -1246,6 +1253,7 @@ int rtnl_listen(struct rtnl_handle *rtnl, } iov.iov_len = sizeof(buf); + msg.msg_namelen = sizeof(nladdr); status = recvmsg(rtnl->fd, &msg, 0); if (status < 0) { @@ -1261,12 +1269,8 @@ int rtnl_listen(struct rtnl_handle *rtnl, fprintf(stderr, "EOF on netlink\n"); return -1; } - if (msg.msg_namelen != sizeof(nladdr)) { - fprintf(stderr, - "Sender address length == %d\n", - msg.msg_namelen); - exit(1); - } + if (!rtnl_from_kernel(&msg)) + continue; if (rtnl->flags & RTNL_HANDLE_F_LISTEN_ALL_NSID) { memset(&ctrl, 0, sizeof(ctrl)); diff --git a/lib/mnl_utils.c b/lib/mnl_utils.c index 44e54aa8..8ddf2b90 100644 --- a/lib/mnl_utils.c +++ b/lib/mnl_utils.c @@ -5,6 +5,7 @@ #include #include +#include #include #include @@ -111,6 +112,38 @@ static mnl_cb_t mnlu_cb_array[NLMSG_MIN_TYPE] = { [NLMSG_OVERRUN] = mnlu_cb_noop, }; +/* + * Like mnl_socket_recvfrom(), but discards datagrams that were + * not sent by the kernel. + */ +ssize_t mnlu_socket_recvfrom(const struct mnl_socket *nl, void *buf, size_t buf_size) +{ + struct sockaddr_nl addr; + struct iovec iov = { + .iov_base = buf, + .iov_len = buf_size, + }; + struct msghdr msg = { + .msg_name = &addr, + .msg_iov = &iov, + .msg_iovlen = 1, + }; + ssize_t ret; + + do { + msg.msg_namelen = sizeof(addr); + ret = recvmsg(mnl_socket_get_fd(nl), &msg, 0); + if (ret < 0) + return ret; + } while (msg.msg_namelen != sizeof(addr) || addr.nl_pid != 0); + + if (msg.msg_flags & MSG_TRUNC) { + errno = ENOSPC; + return -1; + } + return ret; +} + int mnlu_socket_recv_run(struct mnl_socket *nl, unsigned int seq, void *buf, size_t buf_size, mnl_cb_t cb, void *data) { @@ -118,7 +151,7 @@ int mnlu_socket_recv_run(struct mnl_socket *nl, unsigned int seq, void *buf, siz int err; do { - err = mnl_socket_recvfrom(nl, buf, buf_size); + err = mnlu_socket_recvfrom(nl, buf, buf_size); if (err <= 0) break; err = mnl_cb_run2(buf, err, seq, portid, diff --git a/rdma/stat.c b/rdma/stat.c index f2c2d173..01cc171b 100644 --- a/rdma/stat.c +++ b/rdma/stat.c @@ -735,7 +735,7 @@ static int stat_one_qp_unbind(struct rd *rd) * then rd_recv_msg() always return -1 here */ portid = mnl_socket_get_portid(rd->nl); - ret = mnl_socket_recvfrom(rd->nl, buf, sizeof(buf)); + ret = mnlu_socket_recvfrom(rd->nl, buf, sizeof(buf)); if (ret <= 0) return ret; -- 2.53.0