Re: [PATCH bpf-next 2/3] libbpf: add error reporting in XDP

[Alexei Starovoitov]

On Mon, Dec 25, 2017 at 11:13:24PM +0100, Eric Leblond wrote:
> Parse netlink ext attribute to get the error message returned by
> the card.
> 
> Signed-off-by: Eric Leblond 
...
> diff --git a/tools/lib/bpf/nlattr.c b/tools/lib/bpf/nlattr.c
> new file mode 100644
> index ..962de14f74e3
> --- /dev/null
> +++ b/tools/lib/bpf/nlattr.c
> @@ -0,0 +1,188 @@
> +
> +/*
> + * NETLINK  Netlink attributes
> + *
> + *   Authors:Thomas Graf 
> + *   Alexey Kuznetsov 
> + */
...
> diff --git a/tools/lib/bpf/nlattr.h b/tools/lib/bpf/nlattr.h
> new file mode 100644
> index ..b95f3e64c14d
> --- /dev/null
> +++ b/tools/lib/bpf/nlattr.h
> @@ -0,0 +1,164 @@
> +#ifndef __NLATTR_H
> +#define __NLATTR_H

Every file in kernel repo has to have SPDX license identifier.
Also note that tools/lib/bpf is LGPL whereas _if_ you're copying
these functions from kernel lib/nlattr.c then it's GPL which we cannot mix.
Probably easier to copy from libnl instead which is LGPL.

[PATCH bpf-next 2/3] libbpf: add error reporting in XDP

[Eric Leblond]

Parse netlink ext attribute to get the error message returned by
the card.

Signed-off-by: Eric Leblond 
---
 tools/lib/bpf/Build|   2 +-
 tools/lib/bpf/bpf.c|   9 +++
 tools/lib/bpf/nlattr.c | 188 +
 tools/lib/bpf/nlattr.h | 164 ++
 4 files changed, 362 insertions(+), 1 deletion(-)
 create mode 100644 tools/lib/bpf/nlattr.c
 create mode 100644 tools/lib/bpf/nlattr.h

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 1e3cfe6b9fce..cfd30a0cbce4 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -26,6 +26,7 @@
 #include 
 #include "bpf.h"
 #include "libbpf.h"
+#include "nlattr.h"
 #include 
 #include 
 #include 
@@ -436,6 +437,7 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
struct nlmsghdr *nh;
struct nlmsgerr *err;
socklen_t addrlen;
+   int one;
 
memset(, 0, sizeof(sa));
sa.nl_family = AF_NETLINK;
@@ -445,6 +447,12 @@ int bpf_set_link_xdp_fd(int ifindex, int fd, __u32 flags)
return -errno;
}
 
+   if (setsockopt(sock, SOL_NETLINK, NETLINK_EXT_ACK,
+  , sizeof(one)) < 0) {
+   /* debug/verbose message that it is not supported */
+   fprintf(stderr, "Netlink error reporting not supported\n"); 
+   }
+
if (bind(sock, (struct sockaddr *), sizeof(sa)) < 0) {
ret = -errno;
goto cleanup;
@@ -521,6 +529,7 @@ 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 ..962de14f74e3
--- /dev/null
+++ b/tools/lib/bpf/nlattr.c
@@ -0,0 +1,188 @@
+
+/*
+ * NETLINK  Netlink attributes
+ *
+ * Authors:Thomas Graf 
+ * Alexey Kuznetsov 
+ */
+
+#include 
+#include "nlattr.h"
+#include 
+#include 
+#include 
+
+static const __u8 nla_attr_minlen[NLA_TYPE_MAX+1] = {
+   [NLA_U8]= sizeof(__u8),
+   [NLA_U16]   = sizeof(__u16),
+   [NLA_U32]   = sizeof(__u32),
+   [NLA_U64]   = sizeof(__u64),
+   [NLA_MSECS] = sizeof(__u64),
+   [NLA_NESTED]= NLA_HDRLEN,
+   [NLA_S8]= sizeof(__s8),
+   [NLA_S16]   = sizeof(__s16),
+   [NLA_S32]   = sizeof(__s32),
+   [NLA_S64]   = sizeof(__s64),
+};
+
+static int validate_nla(const struct nlattr *nla, int maxtype,
+   const struct nla_policy *policy)
+{
+   const struct nla_policy *pt;
+   int minlen = 0, attrlen = nla_len(nla), type = nla_type(nla);
+
+   if (type <= 0 || type > maxtype)
+   return 0;
+
+   pt = [type];
+
+   if (pt->type > NLA_TYPE_MAX)
+   return -EINVAL;
+
+   switch (pt->type) {
+   case NLA_FLAG:
+   if (attrlen > 0)
+   return -ERANGE;
+   break;
+
+   case NLA_NUL_STRING:
+   if (pt->len)
+   minlen = min(attrlen, pt->len + 1);
+   else
+   minlen = attrlen;
+
+   if (!minlen || memchr(nla_data(nla), '\0', minlen) == NULL)
+   return -EINVAL;
+   /* fall through */
+
+   case NLA_STRING:
+   if (attrlen < 1)
+   return -ERANGE;
+
+   if (pt->len) {
+   char *buf = nla_data(nla);
+
+   if (buf[attrlen - 1] == '\0')
+   attrlen--;
+
+   if (attrlen > pt->len)
+   return -ERANGE;
+   }
+   break;
+
+   case NLA_BINARY:
+   if (pt->len && attrlen > pt->len)
+   return -ERANGE;
+   break;
+
+   case NLA_NESTED_COMPAT:
+   if (attrlen < pt->len)
+   return -ERANGE;
+   if (attrlen < NLA_ALIGN(pt->len))
+   break;
+   if (attrlen < NLA_ALIGN(pt->len) + NLA_HDRLEN)
+   return -ERANGE;
+   nla = nla_data(nla) + NLA_ALIGN(pt->len);
+   if (attrlen < NLA_ALIGN(pt->len) + NLA_HDRLEN + nla_len(nla))
+   return -ERANGE;
+   break;
+   case NLA_NESTED:
+   /* a nested attributes is allowed to be