netdev - Re: [PATCH iproute2] ss: Fix allocation of cong control alg name

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Date:	Fri, 29 May 2015 04:04:05 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vadim Kochan <vadim4j@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH iproute2] ss: Fix allocation of cong control alg name

On Fri, 2015-05-29 at 13:30 +0300, Vadim Kochan wrote:
> From: Vadim Kochan <vadim4j@...il.com>
> 
> Use strdup instead of malloc, and get rid of bad strcpy.
> 
> Signed-off-by: Vadim Kochan <vadim4j@...il.com>
> ---
>  misc/ss.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/misc/ss.c b/misc/ss.c
> index 347e3a1..a719466 100644
> --- a/misc/ss.c
> +++ b/misc/ss.c
> @@ -1908,8 +1908,7 @@ 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);
> +			s.cong_alg = strdup(cong_attr);
>  		}
>  
>  		if (TCPI_HAS_OPT(info, TCPI_OPT_WSCALE)) {

I doubt TCP_CA_NAME_MAX will ever change in the kernel : 16 bytes.

Its typically "cubic" and less than 8 bytes.

Using 8 bytes to point to a malloc(8) is a waste.

Please remove the memory allocation, or store the pointer, since
tcp_show_info() does the malloc()/free() before return.

diff --git a/misc/ss.c b/misc/ss.c
index 347e3a1..9fe229f 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);
@@ -1906,11 +1906,10 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r,
 			s.has_fastopen_opt = TCPI_HAS_OPT(info, TCPI_OPT_SYN_DATA);
 		}
 
-		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);
-		}
+		if (tb[INET_DIAG_CONG])
+			strncpy(s.cong_alg,
+				rta_getattr_str(tb[INET_DIAG_CONG]),
+				sizeof(s.cong_alg) - 1);
 
 		if (TCPI_HAS_OPT(info, TCPI_OPT_WSCALE)) {
 			s.has_wscale_opt  = true;
@@ -1984,8 +1983,6 @@ 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);
 	}
 }
 


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