tools: bpftool: fix truncated netlink dumps

PATCH Applied Jakub Kicinski 3 participants 3 messages Feb 17 – Feb 18

Subsystems (3)

BPF libbpf bpftool

lore

Share & tools

lore

Jakub Kicinski

author

2026-02-17 19:41 UTC #0 lore raw

PATCH v3 1/1 tools: bpftool: fix truncated netlink dumps

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 <[email protected]>

Fixes 7084566a236f ("tools/bpftool: Remove libbpf_internal.h usage in bpftool")

Signed-off-by Jakub Kicinski <[email protected]>

---
v3:
- add missing new line
v2: https://lore.kernel.org/[email protected]
- make the same change in libbpf_netlink_recv()
note that libbpf_netlink_recv() does a PEEK and then realloc if the message is larger, so it's technically already safe but probably better if we are consistent
- fprintf(stderr) -> p_err()
- adjust msg
v1: https://lore.kernel.org/bpf/[email protected]/

CC [email protected]

---
 tools/bpf/bpftool/net.c | 5 ++++-
 tools/lib/bpf/netlink.c | 4 +++-
 2 files changed, 7 insertions(+), 2 deletions(-)

tools/bpf/bpftool/net.c +4 -1

index f25d66c8395e..974189da8a91 100644
@@ -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:

tools/lib/bpf/netlink.c +3 -1

index c997e69d507f..c9a78fb16f11 100644
@@ -143,7 +143,7 @@ static int libbpf_netlink_recv(int sock, __u32 nl_pid, int seq,
 	struct nlmsghdr *nh;
 	int len, ret;
 
-	ret = alloc_iov(&iov, 4096);
+	ret = alloc_iov(&iov, 8192);
 	if (ret)
 		goto done;

@@ -212,6 +212,8 @@ static int libbpf_netlink_recv(int sock, __u32 nl_pid, int seq,
 				}
 			}
 		}
+		if (len)
+			pr_warn("Invalid message or trailing data in Netlink response: %d bytes left\n", len);
 	}
 	ret = 0;
 done:

Signature · 1 line

2.53.0

Alexei Starovoitov

Applied

2026-02-18 00:56 UTC #1 lore raw

Quoted 9 lines · Jakub Kicinski

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 <[email protected]>
Fixes 7084566a236f ("tools/bpftool: Remove libbpf_internal.h usage in bpftool")
Signed-off-by Jakub Kicinski <[email protected]>

Applied to bpf tree.

[email protected]

CI Applied

2026-02-18 01:00 UTC #2 lore raw

In reply to Jakub Kicinski

This patch was applied to bpf/bpf.git (master) by Alexei Starovoitov <[email protected]>:

Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <[email protected]>:

Quoted 10 lines · On Tue, 17 Feb 2026 11:41:50 -0800 you wrote:

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 <[email protected]>
Fixes 7084566a236f ("tools/bpftool: Remove libbpf_internal.h usage in bpftool")
Signed-off-by Jakub Kicinski <[email protected]>
[...]

Here is the summary with links:
- [bpf,v3] tools: bpftool: fix truncated netlink dumps

    https://git.kernel.org/bpf/bpf/c/3b39d73cc337

You are awesome, thank you!

Signature · 2 lines

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