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@xxxxxxxxx>
> ---
> 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@xxxxxxxxx
> 
> To: Andrii Nakryiko <andrii@xxxxxxxxxx>
> To: Eduard Zingerman <eddyz87@xxxxxxxxx>
> To: Ihor Solodrai <ihor.solodrai@xxxxxxxxx>
> To: Alexei Starovoitov <ast@xxxxxxxxxx>
> To: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> To: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> To: Martin KaFai Lau <martin.lau@xxxxxxxxx>
> To: Song Liu <song@xxxxxxxxxx>
> To: Yonghong Song <yonghong.song@xxxxxxxxx>
> To: Jiri Olsa <jolsa@xxxxxxxxxx>
> To: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>
> Cc: bpf@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---

Acked-by: Mykyta Yatsenko <yatsenko@xxxxxxxx>

>  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@xxxxxxxxx>
>