netdev - Re: [PATCH iproute2 v2 1/2] bpf: Fix segfault when custom pinning is used

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Date:   Wed, 22 Apr 2020 09:35:31 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     netdev@...r.kernel.org, dsahern@...il.com, aclaudi@...hat.com,
        daniel@...earbox.net, asmadeus@...ewreck.org,
        Jamal Hadi Salim <hadi@...atatu.com>
Subject: Re: [PATCH iproute2 v2 1/2] bpf: Fix segfault when custom pinning
 is used

On Wed, 22 Apr 2020 06:28:07 -0400
Jamal Hadi Salim <jhs@...atatu.com> wrote:

> From: Jamal Hadi Salim <hadi@...atatu.com>
> 

This is not a sufficient commit message. You need to describe what the
problem is and why this fixes it.


> Fixes: c0325b06382 ("bpf: replace snprintf with asprintf when dealing with long buffers")
> 
> Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
> ---
>  lib/bpf.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/bpf.c b/lib/bpf.c
> index 10cf9bf4..656cad02 100644
> --- a/lib/bpf.c
> +++ b/lib/bpf.c
> @@ -1509,15 +1509,15 @@ out:
>  static int bpf_make_custom_path(const struct bpf_elf_ctx *ctx,
>  				const char *todo)
>  {
> -	char *tmp = NULL;
> +	char tmp[PATH_MAX] = {};

Initializing the whole string to 0 is over kill here.

>  	char *rem = NULL;
>  	char *sub;
>  	int ret;
>  
> -	ret = asprintf(&tmp, "%s/../", bpf_get_work_dir(ctx->type));
> +	ret = snprintf(tmp, PATH_MAX, "%s/../", bpf_get_work_dir(ctx->type));

snprintf will never return -1.

>  	if (ret < 0) {
> -		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
> -		goto out;
> +		fprintf(stderr, "snprintf failed: %s\n", strerror(errno));
> +		return ret;
>  	}
>  
>  	ret = asprintf(&rem, "%s/", todo);
> @@ -1547,7 +1547,6 @@ static int bpf_make_custom_path(const struct bpf_elf_ctx *ctx,
>  	ret = 0;
>  out:
>  	free(rem);
> -	free(tmp);
>  	return ret;
>  }
>  

This patch needs to be reworked.