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If the snprintf in ifcmd_raw() fails, then we can restore the buffer to

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its original state by zeroing out the data that was appended to the buffer
by the failed snprintf.

This trick allows ifcmd_raw() to never fail in a way that would attach
corrupt commands to the output buffer.
This commit is contained in:
Nicholas J. Kain 2014-03-19 06:14:50 -04:00
parent a2e8136bc9
commit 2de848f2c7
1 changed files with 7 additions and 8 deletions
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15
ndhc/ifchange.c
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@ -59,8 +59,12 @@ static int ifcmd_raw(char *buf, size_t buflen, char *optname,
int ioptlen = (int)optlen;
ssize_t olen = snprintf(buf, buflen, "%s:%.*s;",
optname, ioptlen, optdata);
if (olen < 0 || (size_t)olen >= buflen)
return -2;
if (olen < 0 || (size_t)olen >= buflen) {
log_warning("%s: (%s) '%s' option would truncate, so it was dropped.",
client_config.interface, __func__, optname);
memset(buf, 0, buflen);
return -1;
}
return olen;
}
@ -306,13 +310,8 @@ static size_t send_cmd(char *out, size_t olen, struct dhcpmsg *packet,
oldlen = get_dhcp_opt(&cfg_packet, code, olddata, sizeof olddata);
if (oldlen == optlen && !memcmp(optdata, olddata, optlen))
return 0;
int r = ifchd_cmd(buf, sizeof buf, optdata, optlen, code);
if (r == -1)
if (ifchd_cmd(buf, sizeof buf, optdata, optlen, code) < 0)
return 0;
else if (r < -1) {
log_warning("Error happened generating ifch cmd string.");
return 0;
}
strnkcat(out, buf, olen);
return strlen(buf);
}