vnc: avoid underflow when accessing user-provided address

If hostlen is zero, there is a possibility that addrstr[hostlen - 1]
underflows and, if a closing bracked is there, hostlen - 2 is passed
to g_strndup() on the next line.  If websocket==false then
addrstr[0] would be a colon, but if websocket==true this could in
principle happen.

Fix it by checking hostlen.

Reported by Coverity.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 3f9c41c5df9617510d8533cf6588172efb3df34b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/ui/vnc.c b/ui/vnc.c
index bbd8b6baaeca46effb69eed9c255271856c7a2b0..9d8a24dd8a690fd2c7822c2eb9af9c250781c23b 100644 (file)
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -3751,7 +3751,7 @@ static int vnc_display_get_address(const char *addrstr,
 
         addr->type = SOCKET_ADDRESS_TYPE_INET;
         inet = &addr->u.inet;
-        if (addrstr[0] == '[' && addrstr[hostlen - 1] == ']') {
+        if (hostlen && addrstr[0] == '[' && addrstr[hostlen - 1] == ']') {
             inet->host = g_strndup(addrstr + 1, hostlen - 2);
         } else {
             inet->host = g_strndup(addrstr, hostlen);