bpftool: Fix truncated netlink dumps

kuba-moo · qmonnet · commit f38edf17bc0e · 2026-03-13T03:28:46.000Z
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. Acked-by: Quentin Monnet <qmo@kernel.org> Fixes: 7084566a236f ("tools/bpftool: Remove libbpf_internal.h usage in bpftool") Signed-off-by: Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/r/20260217194150.734701-1-kuba@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/src/net.c b/src/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 +201,9 @@ static int netlink_recv(int sock, __u32 nl_pid, __u32 seq,
 					return ret;
 			}
 		}
+
+		if (len)
+			p_err("Invalid message or trailing data in Netlink response: %d bytes left", len);
 	}
 	ret = 0;
 done:

Original file line number	Diff line number	Diff line change
`@@ -156,7 +156,7 @@ static int netlink_recv(int sock, __u32 nl_pid, __u32 seq,`
`156`	`156`	`bool multipart = true;`
`157`	`157`	`struct nlmsgerr *err;`
`158`	`158`	`struct nlmsghdr *nh;`
`159`		`- char buf[4096];`
	`159`	`+ char buf[8192];`
`160`	`160`	`int len, ret;`
`161`	`161`
`162`	`162`	`while (multipart) {`
`@@ -201,6 +201,9 @@ static int netlink_recv(int sock, __u32 nl_pid, __u32 seq,`
`201`	`201`	`return ret;`
`202`	`202`	`}`
`203`	`203`	`}`
	`204`	`+`
	`205`	`+ if (len)`
	`206`	`+ p_err("Invalid message or trailing data in Netlink response: %d bytes left", len);`
`204`	`207`	`}`
`205`	`208`	`ret = 0;`
`206`	`209`	`done:`