netdev - Re: [PATCH iproute2-next] bpf: fix snprintf truncation warning

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Date:   Wed, 4 Sep 2019 18:28:53 +0200
From:   Andrea Claudi <aclaudi@...hat.com>
To:     linux-netdev <netdev@...r.kernel.org>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH iproute2-next] bpf: fix snprintf truncation warning

On Wed, Sep 4, 2019 at 5:50 PM Andrea Claudi <aclaudi@...hat.com> wrote:
>
> gcc v9.2.1 produces the following warning compiling iproute2:
>
> bpf.c: In function ‘bpf_get_work_dir’:
> bpf.c:784:49: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
>   784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
>       |                                                 ^
> bpf.c:784:2: note: ‘snprintf’ output between 2 and 4097 bytes into a destination of size 4096
>   784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Fix it extending bpf_wrk_dir size by 1 byte for the extra "/" char.
>
> Signed-off-by: Andrea Claudi <aclaudi@...hat.com>
> ---
>  lib/bpf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/bpf.c b/lib/bpf.c
> index 7d2a322ffbaec..95de7894a93ce 100644
> --- a/lib/bpf.c
> +++ b/lib/bpf.c
> @@ -742,7 +742,7 @@ static int bpf_gen_hierarchy(const char *base)
>  static const char *bpf_get_work_dir(enum bpf_prog_type type)
>  {
>         static char bpf_tmp[PATH_MAX] = BPF_DIR_MNT;
> -       static char bpf_wrk_dir[PATH_MAX];
> +       static char bpf_wrk_dir[PATH_MAX + 1];
>         static const char *mnt;
>         static bool bpf_mnt_cached;
>         const char *mnt_env = getenv(BPF_ENV_MNT);
> --
> 2.21.0
>

Sorry, I forgot to add:

Fixes: e42256699cac ("bpf: make tc's bpf loader generic and move into lib")