[PATCH iproute2 1/5] netlink: use a counter for sequence numbers

[Stephen Hemminger <stephen@networkplumber.org>]

Seeding the sequence number from time() breaks with a 32-bit time_t
after 2038: time() returns -1, the first request gets sequence zero,
and the range check in __rtnl_talk_iov() underflows, leaving ip
blocked in recvmsg(). The seed adds nothing since replies are already
matched by port id.

Drop the seed so libnetlink starts at 1, make the range check
wrap-safe, and replace the per-message time() in the mnl helpers with
a counter that starts at 1 and skips zero.

Reported-by: Florian Fainelli <f.fainelli@gmail.com>
Reported-by: Anthropic OSS scanner (ANT-2026-E6IHJA62)
Reported-by: Anthropic OSS scanner (ANT-2026-1UC2GBCD)
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 include/mnl_utils.h |  1 +
 lib/libnetlink.c    |  4 +---
 lib/mnl_utils.c     | 13 +++++++++++--
 rdma/utils.c        |  2 +-
 4 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/mnl_utils.h b/include/mnl_utils.h
index 4df9e398..d809383c 100644
--- a/include/mnl_utils.h
+++ b/include/mnl_utils.h
@@ -25,6 +25,7 @@ int mnlu_gen_socket_sndrcv(struct mnlu_gen_socket *nlg, const struct nlmsghdr *n
 
 struct mnl_socket *mnlu_socket_open(int bus);
 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);
 int mnlu_socket_recv_run(struct mnl_socket *nl, unsigned int seq, void *buf, size_t buf_size,
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index edf3a8ba..6ff9cace 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -15,7 +15,6 @@
 #include <netinet/in.h>
 #include <string.h>
 #include <errno.h>
-#include <time.h>
 #include <sys/uio.h>
 #include <linux/fib_rules.h>
 #include <linux/if_addrlabel.h>
@@ -246,7 +245,6 @@ int rtnl_open_byproto(struct rtnl_handle *rth, unsigned int subscriptions,
 			rth->local.nl_family);
 		goto err;
 	}
-	rth->seq = time(NULL);
 	return 0;
 err:
 	rtnl_close(rth);
@@ -1092,7 +1090,7 @@ next:
 
 			if (nladdr.nl_pid != 0 ||
 			    h->nlmsg_pid != rtnl->local.nl_pid ||
-			    h->nlmsg_seq > seq || h->nlmsg_seq < seq - iovlen) {
+			    (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));
diff --git a/lib/mnl_utils.c b/lib/mnl_utils.c
index 43b4cd1a..44e54aa8 100644
--- a/lib/mnl_utils.c
+++ b/lib/mnl_utils.c
@@ -5,7 +5,6 @@
 
 #include <errno.h>
 #include <string.h>
-#include <time.h>
 #include <libmnl/libmnl.h>
 #include <linux/genetlink.h>
 
@@ -40,6 +39,16 @@ int mnl_add_nl_group(struct mnl_socket *nl, unsigned int group)
 	return mnl_socket_bind(nl, group, MNL_SOCKET_AUTOPID);
 }
 
+/* Sequence number for next request, zero is reserved for kernel events */
+uint32_t mnlu_next_seq(void)
+{
+	static uint32_t seq;
+
+	if (++seq == 0)
+		seq = 1;
+	return seq;
+}
+
 struct nlmsghdr *mnlu_msg_prepare(void *buf, uint32_t nlmsg_type, uint16_t flags,
 				  void *extra_header, size_t extra_header_size)
 {
@@ -49,7 +58,7 @@ struct nlmsghdr *mnlu_msg_prepare(void *buf, uint32_t nlmsg_type, uint16_t flags
 	nlh = mnl_nlmsg_put_header(buf);
 	nlh->nlmsg_type = nlmsg_type;
 	nlh->nlmsg_flags = flags;
-	nlh->nlmsg_seq = time(NULL);
+	nlh->nlmsg_seq = mnlu_next_seq();
 
 	eh = mnl_nlmsg_put_extra_header(nlh, extra_header_size);
 	memcpy(eh, extra_header, extra_header_size);
diff --git a/rdma/utils.c b/rdma/utils.c
index f6605eef..a85e8422 100644
--- a/rdma/utils.c
+++ b/rdma/utils.c
@@ -685,7 +685,7 @@ int rd_exec_cmd(struct rd *rd, const struct rd_cmd *cmds, const char *str)
 
 void rd_prepare_msg(struct rd *rd, uint32_t cmd, uint32_t *seq, uint16_t flags)
 {
-	*seq = time(NULL);
+	*seq = mnlu_next_seq();
 
 	rd->nlh = mnl_nlmsg_put_header(rd->buff);
 	rd->nlh->nlmsg_type = RDMA_NL_GET_TYPE(RDMA_NL_NLDEV, cmd);
-- 
2.53.0