tree e58c6519f8e825a9feb2367660126bdff6dbfeb1
parent f1c668268e9ddaedd8d78d7ae44cd26db1e8469f
author Pablo Neira Ayuso <pablo@netfilter.org> 1343610531 +0200
committer Pablo Neira Ayuso <pablo@netfilter.org> 1343612212 +0200

iptables-restore: fix parameter parsing (shows up with gcc-4.7)

This patch fixes parameter parsing in iptables-restore since time ago. The
problem has shown up with gcc-4.7. This version of gcc seem to perform more
agressive memory management than previous.

Peter Lekensteyn provided the following sample code similar to the one
in iptables-restore:

int i = 0;

for (;;) {
	char x[5];

	x[i] = '0' + i;
	if (++i == 4) {
		x[i] = '\0'; /* terminate string with null byte */
		printf("%s\n", x);
		break;
	}
}

Many may expect 0123 as output. But GCC 4.7 does not do that when compiling
with optimization enabled (-O1 and higher). It instead puts random data in the
first bytes of the character array, which becomes:

| 0  |  1  |  2  |  3  |  4   |
|     RANDOM     | '3' | '\0' |

Since the array is declared inside the scope of loop's body, you can think of
it as of a new array being allocated in the automatic storage area for each
loop iteration.

The correct code should be:

char x[5];

for (;;) {
	x[i] = '0' + i;
	if (++i == 4) {
		x[i] = '\0'; /* terminate string with null byte */
		printf("%s\n", x);
		break;
	}
}

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>