[PATCH v2 3/4] netlink: decode nlmsgerr attributes

[JingPiao Chen]

* netlink.c: Include "nlattr.h" and "xlat/nlmsgerr_attrs.h".
(print_cookie, decode_nlmsgerr_attr_cookie): New functions.
(nlmsgerr_nla_decoders): New array.
(decode_nlmsgerr): Use it.
* xlat/nlmsgerr_attrs.in: New file.
* NEWS: Mention this.
---
 NEWS                   |  1 +
 netlink.c              | 44 ++++++++++++++++++++++++++++++++++++++++++++
 xlat/nlmsgerr_attrs.in |  4 ++++
 3 files changed, 49 insertions(+)
 create mode 100644 xlat/nlmsgerr_attrs.in

diff --git a/NEWS b/NEWS
index e09e10f..bb199cb 100644
--- a/NEWS
+++ b/NEWS
@@ -15,6 +15,7 @@ Noteworthy changes in release ?.?? (????-??-??)
     packet_diag_msg, and smc_diag_msg netlink attributes of NETLINK_SOCK_DIAG.
   * Implemented NETLINK_SELINUX protocol specific decoding.
   * Implemented decoding of netlink message ack flags.
+  * Implemented decoding of nlmsgerr netlink attributes.
   * Updated lists of BPF_*, RWF_*, SCM_*, and SO_* constants.
 
 * Bug fixes
diff --git a/netlink.c b/netlink.c
index fc440da..7e1154b 100644
--- a/netlink.c
+++ b/netlink.c
@@ -29,6 +29,7 @@
 
 #include "defs.h"
 #include "netlink.h"
+#include "nlattr.h"
 #include <linux/audit.h>
 #include <linux/rtnetlink.h>
 #include <linux/xfrm.h>
@@ -46,6 +47,7 @@
 #include "xlat/nl_selinux_types.h"
 #include "xlat/nl_sock_diag_types.h"
 #include "xlat/nl_xfrm_types.h"
+#include "xlat/nlmsgerr_attrs.h"
 
 /*
  * Fetch a struct nlmsghdr from the given address.
@@ -284,6 +286,38 @@ print_nlmsghdr(struct tcb *tcp,
 	return family != NL_FAMILY_DEFAULT ? family : hdr_family;
 }
 
+static bool
+print_cookie(struct tcb *const tcp,
+	    void *const elem_buf,
+	    const size_t elem_size,
+	    void *const opaque_data)
+{
+	tprintf("%" PRIu8, *(uint8_t *) elem_buf);
+
+	return true;
+}
+
+static bool
+decode_nlmsgerr_attr_cookie(struct tcb *const tcp,
+			    const kernel_ulong_t addr,
+			    const kernel_ulong_t len,
+			    const void *const opaque_data)
+{
+	uint8_t cookie;
+	const size_t nmemb = len / sizeof(cookie);
+
+	print_array(tcp, addr, nmemb, &cookie, sizeof(cookie),
+		    umoven_or_printaddr, print_cookie, 0);
+
+	return true;
+}
+
+static const nla_decoder_t nlmsgerr_nla_decoders[] = {
+	[NLMSGERR_ATTR_MSG]	= decode_nla_str,
+	[NLMSGERR_ATTR_OFFS]	= decode_nla_u32,
+	[NLMSGERR_ATTR_COOKIE]	= decode_nlmsgerr_attr_cookie
+};
+
 static void
 decode_nlmsghdr_with_payload(struct tcb *const tcp,
 			     const int fd,
@@ -332,6 +366,16 @@ decode_nlmsgerr(struct tcb *const tcp,
 			decode_nlmsghdr_with_payload(tcp, fd, family,
 						     &err.msg, addr, payload);
 		}
+
+		addr += payload;
+		len -= payload;
+	}
+	if (len) {
+		tprints(", ");
+		decode_nlattr(tcp, addr, len,
+			      nlmsgerr_attrs, "NLMSGERR_ATTR_???",
+			      nlmsgerr_nla_decoders,
+			      ARRAY_SIZE(nlmsgerr_nla_decoders), NULL);
 	}
 
 	tprints("}");
diff --git a/xlat/nlmsgerr_attrs.in b/xlat/nlmsgerr_attrs.in
new file mode 100644
index 0000000..589bc55
--- /dev/null
+++ b/xlat/nlmsgerr_attrs.in
@@ -0,0 +1,4 @@
+NLMSGERR_ATTR_UNUSED	0
+NLMSGERR_ATTR_MSG	1
+NLMSGERR_ATTR_OFFS	2
+NLMSGERR_ATTR_COOKIE	3
-- 
2.7.4