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[PATCH] libbpf: avoid possible use of uninitialized mod_len

Achill Gilgenast posted 1 patch 2 months, 1 week ago
There is a newer version of this series
tools/lib/bpf/libbpf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
[PATCH] libbpf: avoid possible use of uninitialized mod_len
Posted by Achill Gilgenast 2 months, 1 week ago 
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@pwned.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
Re: [PATCH] libbpf: avoid possible use of uninitialized mod_len
Posted by Yonghong Song 2 months, 1 week ago 

On 7/29/25 2:45 AM, Achill Gilgenast wrote:
> 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@pwned.life>

The code itself is actually okay. The error is triggered due to'maybe-uninitialized'.
To silence the compilation error, I think this change is okay.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

> ---
>   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);
Re: [PATCH] libbpf: avoid possible use of uninitialized mod_len
Posted by Eduard Zingerman 2 months, 1 week ago 
On Tue, 2025-07-29 at 09:17 -0700, Yonghong Song wrote:
> 
> On 7/29/25 2:45 AM, Achill Gilgenast wrote:
> > 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@pwned.life>
> 
> The code itself is actually okay. The error is triggered due to'maybe-uninitialized'.
> To silence the compilation error, I think this change is okay.
> 
> Acked-by: Yonghong Song <yonghong.song@linux.dev>

I agree with Yonghong, `mod_len` is only read if mod_name != NULL,
meaning that "if (fn_name) { ... mod_name = ...; mod_len = ... }"
block was executed.

Please drop the "Fixes" tag.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]
[PATCH] libbpf: avoid possible use of uninitialized mod_len
Posted by Achill Gilgenast 2 months ago 
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;
	      |                     ^~~~~~~

Signed-off-by: Achill Gilgenast <fossdd@pwned.life>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20250729094611.2065713-1-fossdd@pwned.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
Re: [PATCH] libbpf: avoid possible use of uninitialized mod_len
Posted by Achill Gilgenast 2 months ago 
On Fri Aug 1, 2025 at 1:46 PM CEST, Achill Gilgenast wrote:
> 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;
> 	      |                     ^~~~~~~
>
> Signed-off-by: Achill Gilgenast <fossdd@pwned.life>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
> Link: https://lore.kernel.org/bpf/20250729094611.2065713-1-fossdd@pwned.life/

Oops, the subject should've been v2. I forgot to pass -v2 to git
send-email.
Re: [PATCH] libbpf: avoid possible use of uninitialized mod_len
Posted by Alexei Starovoitov 2 months ago 
On Fri, Aug 1, 2025 at 5:05 AM Achill Gilgenast <fossdd@pwned.life> wrote:
>
> On Fri Aug 1, 2025 at 1:46 PM CEST, Achill Gilgenast wrote:
> > 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;
> >             |                     ^~~~~~~
> >
> > Signed-off-by: Achill Gilgenast <fossdd@pwned.life>
> > Acked-by: Yonghong Song <yonghong.song@linux.dev>
> > Acked-by: Eduard Zingerman <eddyz87@gmail.com>
> > Link: https://lore.kernel.org/bpf/20250729094611.2065713-1-fossdd@pwned.life/
>
> Oops, the subject should've been v2. I forgot to pass -v2 to git
> send-email.

No. It was already applied.

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