5 files changed, 272 insertions, 2 deletions

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 64335bb94f9f..ec3fc8d88e87 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -45,7 +45,7 @@ hostprogs-y += xdp_rxq_info
 hostprogs-y += syscall_tp
 
 # Libbpf dependencies
-LIBBPF := ../../tools/lib/bpf/bpf.o
+LIBBPF := ../../tools/lib/bpf/bpf.o ../../tools/lib/bpf/nlattr.o
 CGROUP_HELPERS := ../../tools/testing/selftests/bpf/cgroup_helpers.o
 
 test_lru_dist-objs := test_lru_dist.o $(LIBBPF)
diff --git a/tools/lib/bpf/Build b/tools/lib/bpf/Build
index d8749756352d..64c679d67109 100644
--- a/tools/lib/bpf/Build
+++ b/tools/lib/bpf/Build
@@ -1 +1 @@
-libbpf-y := libbpf.o bpf.o
+libbpf-y := libbpf.o bpf.o nlattr.o
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index bf2772566240..9c88f6e4156d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -32,6 +32,10 @@
 #include <sys/socket.h>
 #include <errno.h>
 
+#ifndef SOL_NETLINK
+#define SOL_NETLINK 270
+#endif
+
 /*
  * When building perf, unistd.h is overridden. __NR_bpf is
  * required to be defined explicitly.
@@ -436,6 +440,7 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
         struct nlmsghdr *nh;
         struct nlmsgerr *err;
         socklen_t addrlen;
+        int one = 1;
 
         memset(&sa, 0, sizeof(sa));
         sa.nl_family = AF_NETLINK;
@@ -445,6 +450,11 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
                 return -errno;
         }
 
+        if (setsockopt(sock, SOL_NETLINK, NETLINK_EXT_ACK,
+                       &one, sizeof(one)) < 0) {
+                fprintf(stderr, "Netlink error reporting not supported\n");
+        }
+
         if (bind(sock, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
                 ret = -errno;
                 goto cleanup;
@@ -521,6 +531,7 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
                         if (!err->error)
                                 continue;
                         ret = err->error;
+                        nla_dump_errormsg(nh);
                         goto cleanup;
                 case NLMSG_DONE:
                         break;
diff --git a/tools/lib/bpf/nlattr.c b/tools/lib/bpf/nlattr.c
new file mode 100644
index 000000000000..4719434278b2
--- /dev/null
+++ b/tools/lib/bpf/nlattr.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: LGPL-2.1
+
+/*
+ * NETLINK      Netlink attributes
+ *
+ *      This library is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU Lesser General Public
+ *      License as published by the Free Software Foundation version 2.1
+ *      of the License.
+ *
+ * Copyright (c) 2003-2013 Thomas Graf <tgraf@suug.ch>
+ */
+
+#include <errno.h>
+#include "nlattr.h"
+#include <linux/rtnetlink.h>
+#include <string.h>
+#include <stdio.h>
+
+static uint16_t nla_attr_minlen[NLA_TYPE_MAX+1] = {
+        [NLA_U8]        = sizeof(uint8_t),
+        [NLA_U16]       = sizeof(uint16_t),
+        [NLA_U32]       = sizeof(uint32_t),
+        [NLA_U64]       = sizeof(uint64_t),
+        [NLA_STRING]    = 1,
+        [NLA_FLAG]      = 0,
+};
+
+static int nla_len(const struct nlattr *nla)
+{
+        return nla->nla_len - NLA_HDRLEN;
+}
+
+static struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
+{
+        int totlen = NLA_ALIGN(nla->nla_len);
+
+        *remaining -= totlen;
+        return (struct nlattr *) ((char *) nla + totlen);
+}
+
+static int nla_ok(const struct nlattr *nla, int remaining)
+{
+        return remaining >= sizeof(*nla) &&
+               nla->nla_len >= sizeof(*nla) &&
+               nla->nla_len <= remaining;
+}
+
+static void *nla_data(const struct nlattr *nla)
+{
+        return (char *) nla + NLA_HDRLEN;
+}
+
+static int nla_type(const struct nlattr *nla)
+{
+        return nla->nla_type & NLA_TYPE_MASK;
+}
+
+static int validate_nla(struct nlattr *nla, int maxtype,
+                        struct nla_policy *policy)
+{
+        struct nla_policy *pt;
+        unsigned int minlen = 0;
+        int type = nla_type(nla);
+
+        if (type < 0 || type > maxtype)
+                return 0;
+
+        pt = &policy[type];
+
+        if (pt->type > NLA_TYPE_MAX)
+                return 0;
+
+        if (pt->minlen)
+                minlen = pt->minlen;
+        else if (pt->type != NLA_UNSPEC)
+                minlen = nla_attr_minlen[pt->type];
+
+        if (nla_len(nla) < minlen)
+                return -1;
+
+        if (pt->maxlen && nla_len(nla) > pt->maxlen)
+                return -1;
+
+        if (pt->type == NLA_STRING) {
+                char *data = nla_data(nla);
+                if (data[nla_len(nla) - 1] != '\0')
+                        return -1;
+        }
+
+        return 0;
+}
+
+static inline int nlmsg_len(const struct nlmsghdr *nlh)
+{
+        return nlh->nlmsg_len - NLMSG_HDRLEN;
+}
+
+/**
+ * Create attribute index based on a stream of attributes.
+ * @arg tb              Index array to be filled (maxtype+1 elements).
+ * @arg maxtype         Maximum attribute type expected and accepted.
+ * @arg head            Head of attribute stream.
+ * @arg len             Length of attribute stream.
+ * @arg policy          Attribute validation policy.
+ *
+ * Iterates over the stream of attributes and stores a pointer to each
+ * attribute in the index array using the attribute type as index to
+ * the array. Attribute with a type greater than the maximum type
+ * specified will be silently ignored in order to maintain backwards
+ * compatibility. If \a policy is not NULL, the attribute will be
+ * validated using the specified policy.
+ *
+ * @see nla_validate
+ * @return 0 on success or a negative error code.
+ */
+static int nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head, int len,
+                     struct nla_policy *policy)
+{
+        struct nlattr *nla;
+        int rem, err;
+
+        memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
+
+        nla_for_each_attr(nla, head, len, rem) {
+                int type = nla_type(nla);
+
+                if (type > maxtype)
+                        continue;
+
+                if (policy) {
+                        err = validate_nla(nla, maxtype, policy);
+                        if (err < 0)
+                                goto errout;
+                }
+
+                if (tb[type])
+                        fprintf(stderr, "Attribute of type %#x found multiple times in message, "
+                                  "previous attribute is being ignored.\n", type);
+
+                tb[type] = nla;
+        }
+
+        err = 0;
+errout:
+        return err;
+}
+
+/* dump netlink extended ack error message */
+int nla_dump_errormsg(struct nlmsghdr *nlh)
+{
+        struct nla_policy extack_policy[NLMSGERR_ATTR_MAX + 1] = {
+                [NLMSGERR_ATTR_MSG]     = { .type = NLA_STRING },
+                [NLMSGERR_ATTR_OFFS]    = { .type = NLA_U32 },
+        };
+        struct nlattr *tb[NLMSGERR_ATTR_MAX + 1], *attr;
+        struct nlmsgerr *err;
+        char *errmsg = NULL;
+        int hlen, alen;
+
+        /* no TLVs, nothing to do here */
+        if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
+                return 0;
+
+        err = (struct nlmsgerr *)NLMSG_DATA(nlh);
+        hlen = sizeof(*err);
+
+        /* if NLM_F_CAPPED is set then the inner err msg was capped */
+        if (!(nlh->nlmsg_flags & NLM_F_CAPPED))
+                hlen += nlmsg_len(&err->msg);
+
+        attr = (struct nlattr *) ((void *) err + hlen);
+        alen = nlh->nlmsg_len - hlen;
+
+        if (nla_parse(tb, NLMSGERR_ATTR_MAX, attr, alen, extack_policy) != 0) {
+                fprintf(stderr,
+                        "Failed to parse extended error attributes\n");
+                return 0;
+        }
+
+        if (tb[NLMSGERR_ATTR_MSG])
+                errmsg = (char *) nla_data(tb[NLMSGERR_ATTR_MSG]);
+
+        fprintf(stderr, "Kernel error message: %s\n", errmsg);
+
+        return 0;
+}
diff --git a/tools/lib/bpf/nlattr.h b/tools/lib/bpf/nlattr.h
new file mode 100644
index 000000000000..931a71f68f93
--- /dev/null
+++ b/tools/lib/bpf/nlattr.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: LGPL-2.1 */
+
+/*
+ * NETLINK      Netlink attributes
+ *
+ *      This library is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU Lesser General Public
+ *      License as published by the Free Software Foundation version 2.1
+ *      of the License.
+ *
+ * Copyright (c) 2003-2013 Thomas Graf <tgraf@suug.ch>
+ */
+
+#ifndef __NLATTR_H
+#define __NLATTR_H
+
+#include <stdint.h>
+#include <linux/netlink.h>
+/* avoid multiple definition of netlink features */
+#define __LINUX_NETLINK_H
+
+/**
+ * Standard attribute types to specify validation policy
+ */
+enum {
+        NLA_UNSPEC,     /**< Unspecified type, binary data chunk */
+        NLA_U8,         /**< 8 bit integer */
+        NLA_U16,        /**< 16 bit integer */
+        NLA_U32,        /**< 32 bit integer */
+        NLA_U64,        /**< 64 bit integer */
+        NLA_STRING,     /**< NUL terminated character string */
+        NLA_FLAG,       /**< Flag */
+        NLA_MSECS,      /**< Micro seconds (64bit) */
+        NLA_NESTED,     /**< Nested attributes */
+        __NLA_TYPE_MAX,
+};
+
+#define NLA_TYPE_MAX (__NLA_TYPE_MAX - 1)
+
+/**
+ * @ingroup attr
+ * Attribute validation policy.
+ *
+ * See section @core_doc{core_attr_parse,Attribute Parsing} for more details.
+ */
+struct nla_policy {
+        /** Type of attribute or NLA_UNSPEC */
+        uint16_t        type;
+
+        /** Minimal length of payload required */
+        uint16_t        minlen;
+
+        /** Maximal length of payload allowed */
+        uint16_t        maxlen;
+};
+
+/**
+ * @ingroup attr
+ * Iterate over a stream of attributes
+ * @arg pos     loop counter, set to current attribute
+ * @arg head    head of attribute stream
+ * @arg len     length of attribute stream
+ * @arg rem     initialized to len, holds bytes currently remaining in stream
+ */
+#define nla_for_each_attr(pos, head, len, rem) \
+        for (pos = head, rem = len; \
+             nla_ok(pos, rem); \
+             pos = nla_next(pos, &(rem)))
+
+int nla_dump_errormsg(struct nlmsghdr *nlh);
+
+#endif /* __NLATTR_H */