netdev - [PATCH bpf-next 4/6] libbpf: fix string comparison for guessing eBPF program type

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Date:   Tue, 16 Jan 2018 15:51:48 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     daniel@...earbox.net, alexei.starovoitov@...il.com
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        Quentin Monnet <quentin.monnet@...ronome.com>
Subject: [PATCH bpf-next 4/6] libbpf: fix string comparison for guessing eBPF program type

From: Quentin Monnet <quentin.monnet@...ronome.com>

libbpf is able to deduce the type of a program from the name of the ELF
section in which it is located. However, the comparison is made on the
first n characters, n being determined with sizeof() applied to the
reference string (e.g. "xdp"). When such section names are supposed to
receive a suffix separated with a slash (e.g. "kprobe/"), using sizeof()
takes the final NUL character of the reference string into account,
which implies that both strings must be equal. Instead, the desired
behaviour would consist in taking the length of the string, *without*
accounting for the ending NUL character, and to make sure the reference
string is a prefix to the ELF section name.

Subtract 1 to the total size of the string for obtaining the length for
the comparison.

Fixes: 583c90097f72 ("libbpf: add ability to guess program type based on section name")
Signed-off-by: Quentin Monnet <quentin.monnet@...ronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e9c4b7cabcf2..30c776375118 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1803,7 +1803,7 @@ BPF_PROG_TYPE_FNS(tracepoint, BPF_PROG_TYPE_TRACEPOINT);
 BPF_PROG_TYPE_FNS(xdp, BPF_PROG_TYPE_XDP);
 BPF_PROG_TYPE_FNS(perf_event, BPF_PROG_TYPE_PERF_EVENT);

-#define BPF_PROG_SEC(string, type) { string, sizeof(string), type }
+#define BPF_PROG_SEC(string, type) { string, sizeof(string) - 1, type }
 static const struct {
 	const char *sec;
 	size_t len;
-- 
2.15.1