Fix denial of service - memory corruption.

CVE-2011-0719

Fix bug #7949 (DoS in Winbind and smbd with many file descriptors open).

All current released versions of Samba are vulnerable to
a denial of service caused by memory corruption. Range
checks on file descriptors being used in the FD_SET macro
were not present allowing stack corruption. This can cause
the Samba code to crash or to loop attempting to select
on a bad file descriptor set.

A connection to a file share, or a local account is needed
to exploit this problem, either authenticated or unauthenticated
(guest connection).

Currently we do not believe this flaw is exploitable
beyond a crash or causing the code to loop, but on the
advice of our security reviewers we are releasing fixes
in case an exploit is discovered at a later date.

1 files changed, 6 insertions, 0 deletions

diff --git a/source/smbd/dnsregister.c b/source/smbd/dnsregister.c
index f02739ef8df..3c689b9cf3e 100644
--- a/source/smbd/dnsregister.c
+++ b/source/smbd/dnsregister.c
@@ -125,6 +125,9 @@ void dns_register_smbd(struct dns_reg_state ** dns_state_ptr,
 	 */
 	if (dns_state->srv_ref != NULL) {
 		mdnsd_conn_fd = DNSServiceRefSockFD(dns_state->srv_ref);
+		if (mdnsd_conn_fd < 0 || mdnsd_conn_fd >= FD_SETSIZE) {
+			return;
+		}
 		FD_SET(mdnsd_conn_fd, listen_set);
 		return;
 	}
@@ -156,6 +159,9 @@ void dns_register_smbd(struct dns_reg_state ** dns_state_ptr,
 	}
 
 	mdnsd_conn_fd = DNSServiceRefSockFD(dns_state->srv_ref);
+	if (mdnsd_conn_fd < 0 || mdnsd_conn_fd >= FD_SETSIZE) {
+		return;
+	}
 	FD_SET(mdnsd_conn_fd, listen_set);
 	*maxfd = MAX(*maxfd, mdnsd_conn_fd);
 	*timeout = timeval_zero();