[PATCH v5 4/4] Netlink: handle multi netlink messages

[Fabien Siron]

This commit handles the case where there are several messages in the buffer.
This is very useful to some protocols like SOCK_DIAG.

* netlink.c (nlmsg_fetch, nlmsg_next): New functions.
(decode_netlink_msg): New function.
(decode_netlink): Call decode_netlink_msg().
* tests/netlink_parsing.c (send_query): Adapt test.
---
 netlink.c               | 45 +++++++++++++++++++++++++++++++++++++++++++--
 tests/netlink_parsing.c |  8 ++++----
 2 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/netlink.c b/netlink.c
index c43f6e7..fecc413 100644
--- a/netlink.c
+++ b/netlink.c
@@ -31,8 +31,34 @@
 #include "xlat/netlink_flags.h"
 #include "xlat/netlink_types.h"
 
-void
-decode_netlink(struct tcb *tcp, unsigned long addr, unsigned long size)
+/* since our target is not in the same process, here are some utils for nlmsg */
+static int
+nlmsg_fetch(struct tcb *tcp, struct nlmsghdr *nlmsghdr, unsigned long addr,
+	    unsigned long len) {
+	if (len < sizeof(struct nlmsghdr)) {
+		if (len != 0)
+			printstr(tcp, addr, len);
+		return 0;
+	}
+
+	if (umove_or_printaddr(tcp, addr, nlmsghdr) == -1)
+		return 0;
+
+	return nlmsghdr->nlmsg_len >= sizeof(struct nlmsghdr) &&
+		nlmsghdr->nlmsg_len <= len;
+}
+
+static unsigned long
+nlmsg_next(struct nlmsghdr *nlmsghdr, unsigned long addr, unsigned long *len) {
+	*len -= NLMSG_ALIGN(nlmsghdr->nlmsg_len);
+
+	return (unsigned long)
+		((char *)(addr) + NLMSG_ALIGN(nlmsghdr->nlmsg_len));
+}
+
+static void
+decode_netlink_msg(struct tcb *tcp, unsigned long addr,
+			    unsigned long size)
 {
 	struct nlmsghdr nlmsghdr;
 
@@ -62,3 +88,18 @@ decode_netlink(struct tcb *tcp, unsigned long addr, unsigned long size)
 
 	tprints("}");
 }
+
+void
+decode_netlink(struct tcb *tcp, unsigned long addr, unsigned long total_size) {
+	struct nlmsghdr nlmsghdr;
+	unsigned long size = total_size;
+
+	for (; nlmsg_fetch(tcp, &nlmsghdr, addr, size);
+	     addr = nlmsg_next(&nlmsghdr, addr, &size)) {
+		if (size != total_size)
+			tprints(", ");
+		tprints("{");
+		decode_netlink_msg(tcp, addr, size);
+		tprints("}");
+	}
+}
diff --git a/tests/netlink_parsing.c b/tests/netlink_parsing.c
index 3e7c983..61957cd 100644
--- a/tests/netlink_parsing.c
+++ b/tests/netlink_parsing.c
@@ -61,8 +61,8 @@ send_query(const int fd)
 	    (unsigned) sizeof(req))
 		perror_msg_and_skip("sendto");
 
-	printf("sendto(%d, {{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
-	       ", seq=0, pid=0}, \"abcd\"}, %u, MSG_DONTWAIT, NULL, 0) = %u\n",
+	printf("sendto(%d, {{{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
+	       ", seq=0, pid=0}, \"abcd\"}}, %u, MSG_DONTWAIT, NULL, 0) = %u\n",
 	       fd, (unsigned) sizeof(req), NLM_F_DUMP,
 	       (unsigned) sizeof(req), (unsigned) sizeof(req));
 
@@ -73,8 +73,8 @@ send_query(const int fd)
 	    (unsigned) sizeof(req.nlh))
 		perror_msg_and_skip("sendto");
 
-	printf("sendto(%d, {{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
-	       ", seq=0, pid=0}}, %u, MSG_DONTWAIT, NULL, 0) = %u\n",
+	printf("sendto(%d, {{{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
+	       ", seq=0, pid=0}}}, %u, MSG_DONTWAIT, NULL, 0) = %u\n",
 	       fd, (unsigned) sizeof(req.nlh), NLM_F_DUMP,
 	       (unsigned) sizeof(req.nlh), (unsigned) sizeof(req.nlh));
 
-- 
2.8.3