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

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Date:   Wed, 22 Apr 2020 14:24:59 +0200
From:   Andrea Claudi <aclaudi@...hat.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        linux-netdev <netdev@...r.kernel.org>,
        David Ahern <dsahern@...il.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, Apr 22, 2020 at 12:28 PM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> From: Jamal Hadi Salim <hadi@...atatu.com>
>
> 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] = {};
>         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));

Shouldn't we check for the last argument length before? We should have
enough space for "/../" and the terminator, so we need the last
argument length to be less than PATH_MAX-5, right?


>         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;
>  }
>
> --
> 2.20.1
>