From mboxrd@z Thu Jan  1 00:00:00 1970
From: Phil Sutter <phil@nwl.cc>
Subject: Re: [PATCH v3] ss: Enclose IPv6 address in brackets
Date: Tue, 1 Aug 2017 16:11:12 +0200
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 <17aba498-3d75-2659-5fdc-4c95b0d214fa@der-flo.net>
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Cc: netdev@vger.kernel.org
To: Florian Lehner <dev@der-flo.net>
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On Tue, Aug 01, 2017 at 12:05:13PM +0200, Florian Lehner wrote:
[...]
> @@ -114,9 +114,13 @@ int addr64_n2a(__u64 addr, char *buff, size_t len);
>  int af_bit_len(int af);
>  int af_byte_len(int af);
> 
> -const char *format_host_r(int af, int len, const void *addr,
> -			       char *buf, int buflen);
> -const char *format_host(int af, int lne, const void *addr);
> +const char *format_host_rb(int af, int len, const void *addr,
> +			       char *buf, int buflen, bool *resolved);
> +#define format_host_r(af, len, addr, buf, buflen) \
> +	format_host_rb(af, len, addr, buf, buflen, NULL)
> +const char *format_host_b(int af, int lne, const void *addr, bool
> *resolved);
> +#define format_host(af, lne, addr) \
> +	format_host_b(af, lne, addr, NULL)
>  #define format_host_rta(af, rta) \
>  	format_host(af, RTA_PAYLOAD(rta), RTA_DATA(rta))
>  const char *rt_addr_n2a_r(int af, int len, const void *addr,
> diff --git a/lib/utils.c b/lib/utils.c
> index 9aa3219..42c3bf5 100644
> --- a/lib/utils.c
> +++ b/lib/utils.c
> @@ -898,8 +898,8 @@ static const char *resolve_address(const void *addr,
> int len, int af)
>  }
>  #endif
> 
> -const char *format_host_r(int af, int len, const void *addr,
> -			char *buf, int buflen)
> +const char *format_host_rb(int af, int len, const void *addr,
> +			char *buf, int buflen, bool *resolved)
>  {
>  #ifdef RESOLVE_HOSTNAMES
>  	if (resolve_hosts) {
> @@ -909,17 +909,20 @@ const char *format_host_r(int af, int len, const
> void *addr,
> 
>  		if (len > 0 &&
>  		    (n = resolve_address(addr, len, af)) != NULL)
> +		{
> +			*resolved = true;
>  			return n;
> +		}
>  	}
>  #endif
>  	return rt_addr_n2a_r(af, len, addr, buf, buflen);
>  }

Did you test that? I guess calling format_host() will lead to
dereference of a NULL pointer.

Cheers, Phil