libxtables: Fix for warning in xtables_ipmask_to_numeric

Gcc complains:

| xtables.c: In function 'xtables_ipmask_to_numeric':
| xtables.c:1491:34: warning: '__builtin___sprintf_chk' may write a terminating nul past the end of the destination [-Wformat-overflow=]
|  1491 |                 sprintf(buf, "/%s", xtables_ipaddr_to_numeric(mask));
|       |                                  ^

Indeed, xtables_ipaddr_to_numeric() returns a pointer to a 20 byte
buffer and xtables_ipmask_to_numeric() writes its content into a buffer
of same size at offset 1. Yet length of returned string is deterministic
as it is an IPv4 address. So shrink it to the minimum of 16 bytes which
eliminates the warning as well.

Fixes: a96166c24eaac ("libxtables: add xtables_ip[6]mask_to_cidr")
Signed-off-by: Phil Sutter <phil@nwl.cc>

diff --git a/libxtables/xtables.c b/libxtables/xtables.c
index 094cbd87ec1edecbbbe4152fd6c6cfc2436e6338..5f47f627df440cddb951ead00e69aa189cd8a04a 100644 (file)
--- a/libxtables/xtables.c
+++ b/libxtables/xtables.c
@@ -1418,7 +1418,7 @@ void xtables_param_act(unsigned int status, const char *p1, ...)
 
 const char *xtables_ipaddr_to_numeric(const struct in_addr *addrp)
 {
-       static char buf[20];
+       static char buf[16];
        const unsigned char *bytep = (const void *)&addrp->s_addr;
 
        sprintf(buf, "%u.%u.%u.%u", bytep[0], bytep[1], bytep[2], bytep[3]);