block/curl: disable extra protocols to prevent CVE-2013-0249

There is a buffer overflow in libcurl POP3/SMTP/IMAP.  The workaround is
simple: disable extra protocols so that they cannot be exploited.  Full
details here:

  http://curl.haxx.se/docs/adv_20130206.html

QEMU only cares about HTTP, HTTPS, FTP, FTPS, and TFTP.  I have tested
that this fix prevents the exploit on my host with
libcurl-7.27.0-5.fc18.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block/curl.c

@@ -34,6 +34,10 @@
 #define DPRINTF(fmt, ...) do { } while (0)
 #endif
 
+#define PROTOCOLS (CURLPROTO_HTTP | CURLPROTO_HTTPS | \
+                   CURLPROTO_FTP | CURLPROTO_FTPS | \
+                   CURLPROTO_TFTP)
+
 #define CURL_NUM_STATES 8
 #define CURL_NUM_ACB    8
 #define SECTOR_SIZE     512
@@ -302,6 +306,13 @@ static CURLState *curl_init_state(BDRVCURLState *s)
     curl_easy_setopt(state->curl, CURLOPT_ERRORBUFFER, state->errmsg);
     curl_easy_setopt(state->curl, CURLOPT_FAILONERROR, 1);
 
+    /* Restrict supported protocols to avoid security issues in the more
+     * obscure protocols.  For example, do not allow POP3/SMTP/IMAP see
+     * CVE-2013-0249.
+     */
+    curl_easy_setopt(state->curl, CURLOPT_PROTOCOLS, PROTOCOLS);
+    curl_easy_setopt(state->curl, CURLOPT_REDIR_PROTOCOLS, PROTOCOLS);
+
 #ifdef DEBUG_VERBOSE
     curl_easy_setopt(state->curl, CURLOPT_VERBOSE, 1);
 #endif