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

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Date:   Tue, 21 Apr 2020 21:38:38 +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,
        Jamal Hadi Salim <hadi@...atatu.com>
Subject: Re: [PATCH iproute2 1/1] bpf: Fix segfault when custom pinning is used

On Tue, Apr 21, 2020 at 8:05 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 | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/lib/bpf.c b/lib/bpf.c
> index 10cf9bf4..cf636c9e 100644
> --- a/lib/bpf.c
> +++ b/lib/bpf.c
> @@ -1509,12 +1509,12 @@ 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 = sprintf(tmp, "%s/../", bpf_get_work_dir(ctx->type));
>         if (ret < 0) {
>                 fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
>                 goto out;
> @@ -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
>

Hi Jamal,
Are you sure this fixes your issue? I think asprintf could segfault
only if ctx is null, but this case is not addressed in your patch.
I remember that Stephen asked me to use asprintf to avoid allocating
huge buffers on stack; anyway I've no objection to sprintf, if needed.

Andrea