[iproute2,v2] ss: Fix allocation of cong control alg name

From: Vadim Kochan <vadim4j@gmail.com>

Used 16 char array for cong alg name instead of malloc.

Fixes: 8250bc9ff4e5 ("ss: Unify inet sockets output")
Reported-by: Jose R. Guzman Mosqueda <jose.r.guzman.mosqueda@intel.com>
Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
---
v2:
   Used 16 byte array for cong alg name instead of malloc
   	suggested by Eric Dumazet <eric.dumazet@gmail.com>

 misc/ss.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

On Fri, 29 May 2015 21:09:54 +0300
Vadim Kochan <vadim4j@gmail.com> wrote:

> From: Vadim Kochan <vadim4j@gmail.com>
> 
> Used 16 char array for cong alg name instead of malloc.
> 
> Fixes: 8250bc9ff4e5 ("ss: Unify inet sockets output")
> Reported-by: Jose R. Guzman Mosqueda <jose.r.guzman.mosqueda@intel.com>
> Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
> ---
> v2:
>    Used 16 byte array for cong alg name instead of malloc
>    	suggested by Eric Dumazet <eric.dumazet@gmail.com>
> 
>  misc/ss.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/misc/ss.c b/misc/ss.c
> index 347e3a1..0bab8a2 100644
> --- a/misc/ss.c
> +++ b/misc/ss.c
> @@ -755,7 +755,7 @@ struct tcpstat
>  	int		    timer;
>  	int		    timeout;
>  	int		    probes;
> -	char		    *cong_alg;
> +	char		    cong_alg[16];
>  	double		    rto, ato, rtt, rttvar;
>  	int		    qack, cwnd, ssthresh, backoff;
>  	double		    send_bps;
> @@ -1664,7 +1664,7 @@ static void tcp_stats_print(struct tcpstat *s)
>  		printf(" ecnseen");
>  	if (s->has_fastopen_opt)
>  		printf(" fastopen");
> -	if (s->cong_alg)
> +	if (s->cong_alg[0])
>  		printf(" %s", s->cong_alg);
>  	if (s->has_wscale_opt)
>  		printf(" wscale:%d,%d", s->snd_wscale, s->rcv_wscale);
> @@ -1907,9 +1907,9 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
>  		}
>  
>  		if (tb[INET_DIAG_CONG]) {
> -			const char *cong_attr = rta_getattr_str(tb[INET_DIAG_CONG]);
> -			s.cong_alg = malloc(strlen(cong_attr + 1));
> -			strcpy(s.cong_alg, cong_attr);
> +			strncpy(s.cong_alg,
> +					rta_getattr_str(tb[INET_DIAG_CONG]),
> +					sizeof(s.cong_alg) - 1);
>  		}
>  
>  		if (TCPI_HAS_OPT(info, TCPI_OPT_WSCALE)) {
> @@ -1984,8 +1984,6 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
>  		tcp_stats_print(&s);
>  		if (s.dctcp)
>  			free(s.dctcp);
> -		if (s.cong_alg)
> -			free(s.cong_alg);
>  	}
>  }
>  

Why not use strdupa? I handles arbitrary size?
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On Fri, 2015-05-29 at 15:02 -0700, Stephen Hemminger wrote:


> Why not use strdupa? I handles arbitrary size?

I doubt this will please security guys.

RETURN VALUE
       The alloca() function returns a pointer to the beginning of the
allocated space.  If the allocation causes stack overflow, program
behavior is undefined.


Could we please stick with this 16 bytes value ?

I am confident we wont increase kernel side because of various backward
compatibility issues anyway.



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