[PATCH v6 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               | 59 ++++++++++++++++++++++++++++++++++++++++++++++---
 tests/netlink_parsing.c | 19 +++++++++++++++-
 2 files changed, 74 insertions(+), 4 deletions(-)

diff --git a/netlink.c b/netlink.c
index c43f6e7..ada6f91 100644
--- a/netlink.c
+++ b/netlink.c
@@ -31,8 +31,37 @@
 #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);
+
+	if (NLMSG_ALIGN(nlmsghdr->nlmsg_len) == 0 ||
+	    NLMSG_ALIGN(nlmsghdr->nlmsg_len) > *len)
+		return 0;
+
+	return (unsigned long)((addr) + NLMSG_ALIGN(nlmsghdr->nlmsg_len));
+}
+
+static void
+decode_netlink_msg(struct tcb *tcp, unsigned long addr,
+			    unsigned long size)
 {
 	struct nlmsghdr nlmsghdr;
 
@@ -57,8 +86,32 @@ decode_netlink(struct tcb *tcp, unsigned long addr, unsigned long size)
 	if (size - sizeof(struct nlmsghdr) > 0) {
 		tprints(", ");
 		printstr(tcp, addr + sizeof(struct nlmsghdr),
-			 size - sizeof(struct nlmsghdr));
+			 nlmsghdr.nlmsg_len - sizeof(struct nlmsghdr));
 	}
 
 	tprints("}");
 }
+
+void
+decode_netlink(struct tcb *tcp, unsigned long addr, unsigned long total_size) {
+	struct nlmsghdr nlmsghdr;
+	unsigned long elt, size = total_size;
+
+	for (elt = 0; nlmsg_fetch(tcp, &nlmsghdr, addr, size);
+	     addr = nlmsg_next(&nlmsghdr, addr, &size), elt++) {
+		if (elt == max_strlen && abbrev(tcp)) {
+			tprints("...");
+			break;
+		}
+		if (size != total_size)
+			tprints(", ");
+		else if (NLMSG_ALIGN(nlmsghdr.nlmsg_len) < total_size)
+			tprints("[");
+		decode_netlink_msg(tcp, addr, size);
+	}
+	if (nlmsghdr.nlmsg_len != (unsigned) -1 &&
+	    nlmsghdr.nlmsg_len != 0 &&
+	    NLMSG_ALIGN(nlmsghdr.nlmsg_len) < total_size) {
+		tprints("]");
+	}
+}
diff --git a/tests/netlink_parsing.c b/tests/netlink_parsing.c
index 3e7c983..657b05d 100644
--- a/tests/netlink_parsing.c
+++ b/tests/netlink_parsing.c
@@ -43,7 +43,7 @@
 static void
 send_query(const int fd)
 {
-	struct {
+	struct req {
 		struct nlmsghdr nlh;
 		char magic[4];
 	} req = {
@@ -54,6 +54,14 @@ send_query(const int fd)
 		},
 		.magic = "abcd"
 	};
+	struct {
+		struct req req1;
+		char padding[NLMSG_ALIGN(sizeof(req)) - sizeof(req)];
+		struct req req2;
+	} reqs = {
+		.req1 = req,
+		.req2 = req
+	};
 
 	const void *const efault = tail_alloc(sizeof(struct nlmsghdr) - 1);
 
@@ -90,6 +98,15 @@ send_query(const int fd)
 
 	printf("sendto(%d, %p, %u, MSG_DONTWAIT, NULL, 0) = -1 "
 	       "EFAULT (%m)\n", fd, efault, (unsigned) sizeof(struct nlmsghdr));
+
+	sendto(fd, &reqs, sizeof(reqs), MSG_DONTWAIT, NULL, 0);
+
+	printf("sendto(%d, [{{len=%u, type=NLMSG_NOOP, flags=NLM_F_REQUEST|0x%x"
+	       ", seq=0, pid=0}, \"abcd\"}, {{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), NLM_F_DUMP,
+	       (unsigned) sizeof(reqs), (unsigned) sizeof(reqs));
 }
 
 int main(void)
-- 
2.8.3