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udhcpc: sanitize hostnames in incoming packets. Closes 3979.
The following options are replaced with string "bad" if they contain malformed hostname: HOST_NAME, DOMAIN_NAME, NIS_DOMAIN, TFTP_SERVER_NAME function old new delta xmalloc_optname_optval 850 888 +38 attach_option 440 443 +3 len_of_option_as_string 13 14 +1 dhcp_option_lengths 13 14 +1 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 4/0 up/down: 43/0) Total: 43 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
parent
53782d9221
commit
7280d2017d
@ -29,9 +29,9 @@ const struct dhcp_optflag dhcp_optflags[] = {
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// { OPTION_IP | OPTION_LIST , 0x07 }, /* DHCP_LOG_SERVER */
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// { OPTION_IP | OPTION_LIST , 0x08 }, /* DHCP_COOKIE_SERVER */
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{ OPTION_IP | OPTION_LIST , 0x09 }, /* DHCP_LPR_SERVER */
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{ OPTION_STRING | OPTION_REQ, 0x0c }, /* DHCP_HOST_NAME */
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{ OPTION_STRING_HOST | OPTION_REQ, 0x0c }, /* DHCP_HOST_NAME */
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{ OPTION_U16 , 0x0d }, /* DHCP_BOOT_SIZE */
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{ OPTION_STRING | OPTION_REQ, 0x0f }, /* DHCP_DOMAIN_NAME */
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{ OPTION_STRING_HOST | OPTION_REQ, 0x0f }, /* DHCP_DOMAIN_NAME */
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{ OPTION_IP , 0x10 }, /* DHCP_SWAP_SERVER */
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{ OPTION_STRING , 0x11 }, /* DHCP_ROOT_PATH */
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{ OPTION_U8 , 0x17 }, /* DHCP_IP_TTL */
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@ -41,7 +41,7 @@ const struct dhcp_optflag dhcp_optflags[] = {
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//server would let us know anyway?
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{ OPTION_IP | OPTION_REQ, 0x1c }, /* DHCP_BROADCAST */
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{ OPTION_IP_PAIR | OPTION_LIST , 0x21 }, /* DHCP_ROUTES */
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{ OPTION_STRING , 0x28 }, /* DHCP_NIS_DOMAIN */
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{ OPTION_STRING_HOST , 0x28 }, /* DHCP_NIS_DOMAIN */
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{ OPTION_IP | OPTION_LIST , 0x29 }, /* DHCP_NIS_SERVER */
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{ OPTION_IP | OPTION_LIST | OPTION_REQ, 0x2a }, /* DHCP_NTP_SERVER */
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{ OPTION_IP | OPTION_LIST , 0x2c }, /* DHCP_WINS_SERVER */
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@ -49,7 +49,7 @@ const struct dhcp_optflag dhcp_optflags[] = {
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{ OPTION_IP , 0x36 }, /* DHCP_SERVER_ID */
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{ OPTION_STRING , 0x38 }, /* DHCP_ERR_MESSAGE */
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//TODO: must be combined with 'sname' and 'file' handling:
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{ OPTION_STRING , 0x42 }, /* DHCP_TFTP_SERVER_NAME */
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{ OPTION_STRING_HOST , 0x42 }, /* DHCP_TFTP_SERVER_NAME */
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{ OPTION_STRING , 0x43 }, /* DHCP_BOOT_FILE */
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//TODO: not a string, but a set of LASCII strings:
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// { OPTION_STRING , 0x4D }, /* DHCP_USER_CLASS */
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@ -148,6 +148,7 @@ const uint8_t dhcp_option_lengths[] ALIGN1 = {
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[OPTION_IP_PAIR] = 8,
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// [OPTION_BOOLEAN] = 1,
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[OPTION_STRING] = 1, /* ignored by udhcp_str2optset */
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[OPTION_STRING_HOST] = 1, /* ignored by udhcp_str2optset */
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#if ENABLE_FEATURE_UDHCP_RFC3397
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[OPTION_DNS_STRING] = 1, /* ignored by both udhcp_str2optset and xmalloc_optname_optval */
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[OPTION_SIP_SERVERS] = 1,
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@ -417,7 +418,9 @@ static NOINLINE void attach_option(
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/* actually 255 is ok too, but adding a space can overlow it */
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existing->data = xrealloc(existing->data, OPT_DATA + 1 + old_len + length);
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if ((optflag->flags & OPTION_TYPE_MASK) == OPTION_STRING) {
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if ((optflag->flags & OPTION_TYPE_MASK) == OPTION_STRING
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|| (optflag->flags & OPTION_TYPE_MASK) == OPTION_STRING_HOST
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) {
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/* add space separator between STRING options in a list */
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existing->data[OPT_DATA + old_len] = ' ';
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old_len++;
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@ -481,6 +484,7 @@ int FAST_FUNC udhcp_str2optset(const char *const_str, void *arg)
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retval = udhcp_str2nip(val, buffer + 4);
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break;
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case OPTION_STRING:
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case OPTION_STRING_HOST:
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#if ENABLE_FEATURE_UDHCP_RFC3397
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case OPTION_DNS_STRING:
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#endif
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@ -80,6 +80,9 @@ enum {
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OPTION_IP = 1,
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OPTION_IP_PAIR,
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OPTION_STRING,
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/* Opts of STRING_HOST type will be sanitized before they are passed
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* to udhcpc script's environment: */
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OPTION_STRING_HOST,
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// OPTION_BOOLEAN,
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OPTION_U8,
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OPTION_U16,
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@ -135,6 +135,63 @@ static int mton(uint32_t mask)
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return i;
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}
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/* Check if a given label represents a valid DNS label
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* Return pointer to the first character after the label upon success,
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* NULL otherwise.
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* See RFC1035, 2.3.1
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*/
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/* We don't need to be particularly anal. For example, allowing _, hyphen
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* at the end, or leading and trailing dots would be ok, since it
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* can't be used for attacks. (Leading hyphen can be, if someone uses
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* cmd "$hostname"
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* in the script: then hostname may be treated as an option)
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*/
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static const char *valid_domain_label(const char *label)
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{
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unsigned char ch;
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unsigned pos = 0;
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for (;;) {
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ch = *label;
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if ((ch|0x20) < 'a' || (ch|0x20) > 'z') {
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if (pos == 0) {
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/* label must begin with letter */
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return NULL;
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}
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if (ch < '0' || ch > '9') {
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if (ch == '\0' || ch == '.')
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return label;
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/* DNS allows only '-', but we are more permissive */
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if (ch != '-' && ch != '_')
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return NULL;
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}
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}
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label++;
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pos++;
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//Do we want this?
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//if (pos > 63) /* NS_MAXLABEL; labels must be 63 chars or less */
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// return NULL;
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}
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}
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/* Check if a given name represents a valid DNS name */
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/* See RFC1035, 2.3.1 */
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static int good_hostname(const char *name)
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{
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//const char *start = name;
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for (;;) {
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name = valid_domain_label(name);
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if (!name)
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return 0;
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if (!name[0])
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return 1;
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//Do we want this?
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//return ((name - start) < 1025); /* NS_MAXDNAME */
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name++;
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}
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}
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/* Create "opt_name=opt_value" string */
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static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_optflag *optflag, const char *opt_name)
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{
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@ -187,8 +244,11 @@ static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_
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* the case of list of options.
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*/
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case OPTION_STRING:
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case OPTION_STRING_HOST:
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memcpy(dest, option, len);
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dest[len] = '\0';
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if (type == OPTION_STRING_HOST && !good_hostname(dest))
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safe_strncpy(dest, "bad", len);
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return ret;
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case OPTION_STATIC_ROUTES: {
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/* Option binary format:
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@ -368,6 +428,7 @@ static char **fill_envp(struct dhcp_packet *packet)
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/* +1 element for each option, +2 for subnet option: */
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if (packet) {
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/* note: do not search for "pad" (0) and "end" (255) options */
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//TODO: change logic to scan packet _once_
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for (i = 1; i < 255; i++) {
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temp = udhcp_get_option(packet, i);
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if (temp) {
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