Re: [PATCH] libbpf: Report error when a negative kprobe offset is specified

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 4/17/26 7:46 PM, Aaron Tomlin wrote:
> In attach_kprobe(), the parsing logic uses sscanf() to extract the
> target function name and offset from the section definition. Currently,
> if a user specifies a negative offset (e.g., SEC("kprobe/func+-100")),
> the input is not explicitly caught and reported as an error.
> 
> This commit updates the logic to explicitly notify the user when a
> negative integer is provided. To facilitate this check, the offset
> variable is changed from unsigned long to long so that sscanf()
> can accurately capture a negative input for evaluation.
> 
> If a negative offset is detected, the loader will now print an
> informative warning stating that the offset must be non-negative,
> and return -EINVAL.
> 
> Additionally, free(func) is called in this new error path to prevent
> a memory leak, as the function name string is dynamically allocated
> by sscanf().
> 
> Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
> ---
>   src/libbpf.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libbpf.c b/src/libbpf.c
> index 42bdba4..cd250fe 100644
> --- a/src/libbpf.c

The upstream of the libbpf is linux kernel repository (tools/lib/bpf). 
Is this patch for libbpf github repo? Please resend for linux kernel.

pw-bot: cr

> +++ b/src/libbpf.c
> @@ -12271,7 +12271,7 @@ error:
>   static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
>   {
>   	DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
> -	unsigned long offset = 0;
> +	long offset = 0;
>   	const char *func_name;
>   	char *func;
>   	int n;
> @@ -12293,6 +12293,13 @@ static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf
>   		pr_warn("kprobe name is invalid: %s\n", func_name);
>   		return -EINVAL;
>   	}
> +
> +	if (offset < 0) {
> +		free(func);
> +		pr_warn("kprobe offset must be a non-negative integer: %li\n", offset);
> +		return -EINVAL;
> +	}
> +
>   	if (opts.retprobe && offset != 0) {
>   		free(func);
>   		pr_warn("kretprobes do not support offset specification\n");