udhcpc: fix OPTION_6RD parsing (could overflow its malloced buffer)
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/common.c b/networking/udhcp/common.c
index bc41c8d..680852c 100644
--- a/networking/udhcp/common.c
+++ b/networking/udhcp/common.c
@@ -142,7 +142,7 @@
* udhcp_str2optset: to determine how many bytes to allocate.
* xmalloc_optname_optval: to estimate string length
* from binary option length: (option[LEN] / dhcp_option_lengths[opt_type])
- * is the number of elements, multiply in by one element's string width
+ * is the number of elements, multiply it by one element's string width
* (len_of_option_as_string[opt_type]) and you know how wide string you need.
*/
const uint8_t dhcp_option_lengths[] ALIGN1 = {
@@ -162,7 +162,18 @@
[OPTION_S32] = 4,
/* Just like OPTION_STRING, we use minimum length here */
[OPTION_STATIC_ROUTES] = 5,
- [OPTION_6RD] = 22, /* ignored by udhcp_str2optset */
+ [OPTION_6RD] = 12, /* ignored by udhcp_str2optset */
+ /* The above value was chosen as follows:
+ * len_of_option_as_string[] for this option is >60: it's a string of the form
+ * "32 128 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff 255.255.255.255 ".
+ * Each additional ipv4 address takes 4 bytes in binary option and appends
+ * another "255.255.255.255 " 16-byte string. We can set [OPTION_6RD] = 4
+ * but this severely overestimates string length: instead of 16 bytes,
+ * it adds >60 for every 4 bytes in binary option.
+ * We cheat and declare here that option is in units of 12 bytes.
+ * This adds more than 60 bytes for every three ipv4 addresses - more than enough.
+ * (Even 16 instead of 12 should work, but let's be paranoid).
+ */
};