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[204.195.112.43]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b0fc1bc1e6sm5641735a91.0.2026.11.08.17.44.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Nov 2026 17:44:40 -0800 (PST) From: Stephen Hemminger To: netdev@vger.kernel.org Cc: dsahern@kernel.org, Stephen Hemminger Subject: [PATCH iproute2 4/5] netlink: handle unpadded last message in receive loops Date: Sun, 8 Nov 2026 17:44:01 -0800 Message-ID: <20261109014434.115922-5-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 The kernel may send a datagram whose last message has no trailing padding, for example Open vSwitch upcalls with OVS_DP_F_UNALIGNED. Subtracting the aligned length then leaves the byte count at -1..-3. __rtnl_talk_iov() and rtnl_listen() compare it as unsigned, read one more header past the datagram and exit with "malformed message"; rtnl_dump_filter_l() exits with "Remnant of size -3". Walk the datagram with NLMSG_OK()/NLMSG_NEXT() everywhere, and treat only a positive rest as a remnant. Reported-by: Anthropic OSS scanner (ANT-2026-S4ZHKVIW) Assisted-by: Claude:claude-opus-5-5 Signed-off-by: Stephen Hemminger --- lib/libnetlink.c | 76 +++++++++++++++++------------------------------- 1 file changed, 27 insertions(+), 49 deletions(-) diff --git a/lib/libnetlink.c b/lib/libnetlink.c index 6432d537..de0681ac 100644 --- a/lib/libnetlink.c +++ b/lib/libnetlink.c @@ -994,7 +994,8 @@ skip_it: fprintf(stderr, "Message truncated\n"); continue; } - if (msglen) { + /* negative if the last message had no padding */ + if (msglen > 0) { fprintf(stderr, "!!!Remnant of size %d\n", msglen); exit(1); } @@ -1088,29 +1089,13 @@ next: if (status < 0) return status; - for (h = (struct nlmsghdr *)buf; status >= sizeof(*h); ) { - int len = h->nlmsg_len; - int l = len - sizeof(*h); - - if (l < 0 || len > status) { - if (msg.msg_flags & MSG_TRUNC) { - fprintf(stderr, "Truncated message\n"); - free(buf); - return -1; - } - fprintf(stderr, - "!!!malformed message: len=%d\n", - len); - exit(1); - } + for (h = (struct nlmsghdr *)buf; NLMSG_OK(h, status); + h = NLMSG_NEXT(h, status)) { + int l = h->nlmsg_len - sizeof(*h); 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); - h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len)); + (unsigned int)(seq - h->nlmsg_seq) >= iovlen) continue; - } if (h->nlmsg_type == NLMSG_ERROR) { struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(h); @@ -1156,21 +1141,23 @@ next: } fprintf(stderr, "Unexpected reply!!!\n"); - - status -= NLMSG_ALIGN(len); - h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len)); } free(buf); + /* negative if the last message had no padding */ + if (status > 0) { + if (msg.msg_flags & MSG_TRUNC) { + fprintf(stderr, "Truncated message\n"); + return -1; + } + fprintf(stderr, "!!!Remnant of size %d\n", status); + exit(1); + } + if (msg.msg_flags & MSG_TRUNC) { fprintf(stderr, "Message truncated\n"); continue; } - - if (status) { - fprintf(stderr, "!!!Remnant of size %d\n", status); - exit(1); - } } } @@ -1294,38 +1281,29 @@ int rtnl_listen(struct rtnl_handle *rtnl, } } - for (h = (struct nlmsghdr *)buf; status >= sizeof(*h); ) { + for (h = (struct nlmsghdr *)buf; NLMSG_OK(h, status); + h = NLMSG_NEXT(h, status)) { int err; - int len = h->nlmsg_len; - int l = len - sizeof(*h); - - if (l < 0 || len > status) { - if (msg.msg_flags & MSG_TRUNC) { - fprintf(stderr, "Truncated message\n"); - return -1; - } - fprintf(stderr, - "!!!malformed message: len=%d\n", - len); - exit(1); - } err = handler(&ctrl, h, jarg); fflush(stdout); if (err < 0) return err; + } - status -= NLMSG_ALIGN(len); - h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len)); + /* negative if the last message had no padding */ + if (status > 0) { + if (msg.msg_flags & MSG_TRUNC) { + fprintf(stderr, "Truncated message\n"); + return -1; + } + fprintf(stderr, "!!!Remnant of size %d\n", status); + exit(1); } if (msg.msg_flags & MSG_TRUNC) { fprintf(stderr, "Message truncated\n"); continue; } - if (status) { - fprintf(stderr, "!!!Remnant of size %d\n", status); - exit(1); - } } } -- 2.53.0