[PATCH bpf] tools: bpftool: fix truncated netlink dumps

[Jakub Kicinski <kuba@kernel.org>]

Netlink requires that the recv buffer used during dumps is at least
min(PAGE_SIZE, 8k) (see the man page). Otherwise the messages will
get truncated. Make sure bpftool follows this requirement, avoid
missing information on systems with large pages.

Fixes: 7084566a236f ("tools/bpftool: Remove libbpf_internal.h usage in bpftool")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: qmo@kernel.org
CC: ast@kernel.org
CC: daniel@iogearbox.net
CC: andrii@kernel.org
CC: martin.lau@linux.dev
CC: eddyz87@gmail.com
CC: song@kernel.org
CC: yonghong.song@linux.dev
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CC: sdf@fomichev.me
CC: haoluo@google.com
CC: jolsa@kernel.org
CC: bpf@vger.kernel.org
---
 tools/bpf/bpftool/net.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/net.c b/tools/bpf/bpftool/net.c
index cfc6f944f7c3..7f248fc01332 100644
--- a/tools/bpf/bpftool/net.c
+++ b/tools/bpf/bpftool/net.c
@@ -156,7 +156,7 @@ static int netlink_recv(int sock, __u32 nl_pid, __u32 seq,
 	bool multipart = true;
 	struct nlmsgerr *err;
 	struct nlmsghdr *nh;
-	char buf[4096];
+	char buf[8192];
 	int len, ret;
 
 	while (multipart) {
@@ -201,6 +201,10 @@ static int netlink_recv(int sock, __u32 nl_pid, __u32 seq,
 					return ret;
 			}
 		}
+
+		if (len)
+	                fprintf(stderr, "Invalid message or trailing data in Netlink response: %d\n",
+				len);
 	}
 	ret = 0;
 done:
-- 
2.52.0