Subject: Re: [Patch] net: fix an array index overflow

From: Eric Dumazet <[email-masked]>
Date: Tue, 01 Dec 2009 09:48:56 +0100

Amerigo Wang a écrit :
> Don't use the address of an out-of-boundary element.
> 
> Maybe this is not harmful at runtime, but it is still
> good to improve it.

Why ?

for (ptr = start; ptr < end; ptr++) {}

is valid, even if 'end' is 'outside of bounds'

It also works if start == end.

> 
> Signed-off-by: WANG Cong <[email-masked]>
> Cc: David S. Miller <[email-masked]>
> 
> ---
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index 57737b8..2669361 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1586,7 +1586,7 @@ static int __init inet_init(void)
>  #endif
>  
>  	/* Register the socket-side information for inet_create. */
> -	for (r = &inetsw[0]; r < &inetsw[SOCK_MAX]; ++r)
> +	for (r = &inetsw[0]; r <= &inetsw[SOCK_MAX-1]; ++r)
>  		INIT_LIST_HEAD(r);
>  
>  	for (q = inetsw_array; q < &inetsw_array[INETSW_ARRAY_LEN]; ++q)
> --

I wonder why you want to 'fix' this loop and let following loop unchanged...

	for (q = inetsw_array; q < &inetsw_array[INETSW_ARRAY_LEN]; ++q)
		inet_register_protosw(q);

If this really hurts your eyes, why not using basic loops ?

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 7d12c6a..476cda7 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1540,8 +1540,7 @@ static struct packet_type ip_packet_type __read_mostly = {
 static int __init inet_init(void)
 {
 	struct sk_buff *dummy_skb;
-	struct inet_protosw *q;
-	struct list_head *r;
+	int i;
 	int rc = -EINVAL;
 
 	BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb));
@@ -1584,11 +1583,11 @@ static int __init inet_init(void)
 #endif
 
 	/* Register the socket-side information for inet_create. */
-	for (r = &inetsw[0]; r < &inetsw[SOCK_MAX]; ++r)
-		INIT_LIST_HEAD(r);
+	for (i = 0; i < SOCK_MAX; i++)
+		INIT_LIST_HEAD(&inetsw[i]);
 
-	for (q = inetsw_array; q < &inetsw_array[INETSW_ARRAY_LEN]; ++q)
-		inet_register_protosw(q);
+	for (i = 0; i < INETSW_ARRAY_LEN; i++)
+		inet_register_protosw(&inetsw_array[i]);
 
 	/*
 	 *	Set the ARP module up