[PATCH bpf-next v2] libbpf: Fix program log buffer size validation

[PATCH bpf-next v2] libbpf: Fix program log buffer size validation

[Luis Vieira]

bpf_program__set_log_buf() checks the existing prog->log_size instead
of the incoming log_size argument when enforcing the UINT_MAX limit.
As a result, an oversized value can be accepted.

The setter also accepts a non-NULL log_buf with a zero log_size, while
bpf_prog_load() rejects mismatched log buffer and size values.

Validate the log buffer and size pair consistently with bpf_prog_load(),
and check the supplied log_size against UINT_MAX.

Signed-off-by: Luis Vieira <luisflavieira@gmail.com>
---
Changes in v2:
- Target bpf-next instead of bpf and drop the Fixes tag.
- Drop the regression selftest.
- Validate log_buf and log_size consistently with bpf_prog_load().
- Link to v1: https://patch.msgid.link/20260914-libbpf-log-buf-fix-v1-1-f592caffcc71@gmail.com

To: Andrii Nakryiko <andrii@kernel.org>
To: Eduard Zingerman <eddyz87@gmail.com>
To: Ihor Solodrai <ihor.solodrai@linux.dev>
To: Alexei Starovoitov <ast@kernel.org>
To: Daniel Borkmann <daniel@iogearbox.net>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
To: Martin KaFai Lau <martin.lau@linux.dev>
To: Song Liu <song@kernel.org>
To: Yonghong Song <yonghong.song@linux.dev>
To: Jiri Olsa <jolsa@kernel.org>
To: Emil Tsalapatis <emil@etsalapatis.com>
Cc: bpf@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 tools/lib/bpf/libbpf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 613afae26519..f7a0517d8fa8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9966,9 +9966,9 @@ const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_siz
 
 int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size)
 {
-	if (log_size && !log_buf)
+	if (!!log_buf != !!log_size)
 		return libbpf_err(-EINVAL);
-	if (prog->log_size > UINT_MAX)
+	if (log_size > UINT_MAX)
 		return libbpf_err(-EINVAL);
 	if (prog->obj->state >= OBJ_LOADED)
 		return libbpf_err(-EBUSY);

---
base-commit: 5ef40d69b38a93bc9951dadb1a15c85c597e1a40
change-id: 20260913-libbpf-log-buf-fix-49f5038caa5d

Best regards,
--  
Luis Vieira <luisflavieira@gmail.com>

Re: [PATCH bpf-next v2] libbpf: Fix program log buffer size validation

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 940 bytes --]

>     libbpf: Fix program log buffer size validation
>
>     bpf_program__set_log_buf() checks the existing prog->log_size instead
>     of the incoming log_size argument when enforcing the UINT_MAX limit.
>     As a result, an oversized value can be accepted.
>
>     The setter also accepts a non-NULL log_buf with a zero log_size, while
>     bpf_prog_load() rejects mismatched log buffer and size values.
>
>     Validate the log buffer and size pair consistently with bpf_prog_load(),
>     and check the supplied log_size against UINT_MAX.
>
>     Signed-off-by: Luis Vieira <luisflavieira@gmail.com>

This looks like a bug fix. Should this include:

  Fixes: 847b98421362 ("adding ci files")


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/35007077686

Re: [PATCH bpf-next v2] libbpf: Fix program log buffer size validation

[Mykyta Yatsenko]

On 9/15/26 7:13 PM, Luis Vieira wrote:
> bpf_program__set_log_buf() checks the existing prog->log_size instead
> of the incoming log_size argument when enforcing the UINT_MAX limit.
> As a result, an oversized value can be accepted.
> 
> The setter also accepts a non-NULL log_buf with a zero log_size, while
> bpf_prog_load() rejects mismatched log buffer and size values.
> 
> Validate the log buffer and size pair consistently with bpf_prog_load(),
> and check the supplied log_size against UINT_MAX.
> 
> Signed-off-by: Luis Vieira <luisflavieira@gmail.com>
> ---
> Changes in v2:
> - Target bpf-next instead of bpf and drop the Fixes tag.
> - Drop the regression selftest.
> - Validate log_buf and log_size consistently with bpf_prog_load().
> - Link to v1: https://patch.msgid.link/20260914-libbpf-log-buf-fix-v1-1-f592caffcc71@gmail.com
> 
> To: Andrii Nakryiko <andrii@kernel.org>
> To: Eduard Zingerman <eddyz87@gmail.com>
> To: Ihor Solodrai <ihor.solodrai@linux.dev>
> To: Alexei Starovoitov <ast@kernel.org>
> To: Daniel Borkmann <daniel@iogearbox.net>
> To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> To: Martin KaFai Lau <martin.lau@linux.dev>
> To: Song Liu <song@kernel.org>
> To: Yonghong Song <yonghong.song@linux.dev>
> To: Jiri Olsa <jolsa@kernel.org>
> To: Emil Tsalapatis <emil@etsalapatis.com>
> Cc: bpf@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---

Acked-by: Mykyta Yatsenko <yatsenko@meta.com>

>  tools/lib/bpf/libbpf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 613afae26519..f7a0517d8fa8 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9966,9 +9966,9 @@ const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_siz
>  
>  int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size)
>  {
> -	if (log_size && !log_buf)
> +	if (!!log_buf != !!log_size)
>  		return libbpf_err(-EINVAL);
> -	if (prog->log_size > UINT_MAX)
> +	if (log_size > UINT_MAX)
>  		return libbpf_err(-EINVAL);
>  	if (prog->obj->state >= OBJ_LOADED)
>  		return libbpf_err(-EBUSY);
> 
> ---
> base-commit: 5ef40d69b38a93bc9951dadb1a15c85c597e1a40
> change-id: 20260913-libbpf-log-buf-fix-49f5038caa5d
> 
> Best regards,
> --  
> Luis Vieira <luisflavieira@gmail.com>
>