linux-kernel - [PATCH] libbpf: avoid possible use of uninitialized mod

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Message-ID: <20250729094611.2065713-1-fossdd@pwned.life>
Date: Tue, 29 Jul 2025 11:45:53 +0200
From: Achill Gilgenast <fossdd@...ed.life>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Viktor Malik <vmalik@...hat.com>,
	bpf@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Achill Gilgenast <fossdd@...ed.life>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>
Subject: [PATCH] libbpf: avoid possible use of uninitialized mod_len

If not fn_name, mod_len does never get initialized which fails now with
gcc15 on Alpine Linux edge:

	libbpf.c: In function 'find_kernel_btf_id.constprop':
	libbpf.c:10100:33: error: 'mod_len' may be used uninitialized [-Werror=maybe-uninitialized]
	10100 |                 if (mod_name && strncmp(mod->name, mod_name, mod_len) != 0)
	      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	libbpf.c:10070:21: note: 'mod_len' was declared here
	10070 |         int ret, i, mod_len;
	      |                     ^~~~~~~

Fixes: 8f8a024272f3 ("libbpf: support "module: Function" syntax for tracing programs")
Signed-off-by: Achill Gilgenast <fossdd@...ed.life>
---
 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 e067cb5776bd..fb4d92c5c339 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10086,27 +10086,27 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd, int t
 	btf__free(btf);
 	if (err <= 0) {
 		pr_warn("%s is not found in prog's BTF\n", name);
 		goto out;
 	}
 out:
 	return err;
 }
 
 static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
 			      enum bpf_attach_type attach_type,
 			      int *btf_obj_fd, int *btf_type_id)
 {
-	int ret, i, mod_len;
+	int ret, i, mod_len = 0;
 	const char *fn_name, *mod_name = NULL;
 
 	fn_name = strchr(attach_name, ':');
 	if (fn_name) {
 		mod_name = attach_name;
 		mod_len = fn_name - mod_name;
 		fn_name++;
 	}
 
 	if (!mod_name || strncmp(mod_name, "vmlinux", mod_len) == 0) {
 		ret = find_attach_btf_id(obj->btf_vmlinux,
 					 mod_name ? fn_name : attach_name,
 					 attach_type);
-- 
2.50.1