path: root/package/samba/samba-3.3.14-CVE-2011-0719.patch

From 724e44eed299c618066dec411530aa9f156119ec Mon Sep 17 00:00:00 2001
From: Karolin Seeger <kseeger@samba.org>
Date: Sun, 27 Feb 2011 18:28:29 +0100
Subject: [PATCH] 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.
---
 source/client/client.c          |    4 +++-
 source/client/dnsbrowse.c       |   12 ++++++++++++
 source/lib/events.c             |   13 +++++++++++++
 source/lib/packet.c             |    5 +++++
 source/lib/readline.c           |    5 +++++
 source/lib/select.c             |    6 ++++++
 source/lib/util_sock.c          |   11 +++++++++--
 source/libaddns/dnssock.c       |    6 +++++-
 source/libsmb/nmblib.c          |    5 +++++
 source/nmbd/nmbd_packets.c      |   24 ++++++++++++++++++++++--
 source/nsswitch/wb_common.c     |   22 ++++++++++++++++++++--
 source/printing/printing.c      |    5 +++++
 source/smbd/dnsregister.c       |    6 ++++++
 source/smbd/oplock.c            |    5 ++++-
 source/smbd/oplock_irix.c       |    5 +++++
 source/smbd/process.c           |    2 +-
 source/smbd/server.c            |   29 +++++++++++++++++++++--------
 source/utils/smbfilter.c        |    8 ++++++--
 source/winbindd/winbindd.c      |   12 +++++++++++-
 source/winbindd/winbindd_dual.c |    7 +++++++
 20 files changed, 171 insertions(+), 21 deletions(-)

diff --git a/source/client/client.c b/source/client/client.c
index 53bd9e6..a989441 100644
--- a/source/client/client.c
+++ b/source/client/client.c
@@ -4379,8 +4379,10 @@ static void readline_callback(void)
 
  again:
 
-	if (cli->fd == -1)
+	if (cli->fd < 0 || cli->fd >= FD_SETSIZE) {
+		errno = EBADF;
 		return;
+	}
 
 	FD_ZERO(&fds);
 	FD_SET(cli->fd,&fds);
diff --git a/source/client/dnsbrowse.c b/source/client/dnsbrowse.c
index 5e3a4de..aa2fb22 100644
--- a/source/client/dnsbrowse.c
+++ b/source/client/dnsbrowse.c
@@ -81,6 +81,11 @@ static void do_smb_resolve(struct mdns_smbsrv_result *browsesrv)
 			TALLOC_FREE(fdset);
 		}
 
+		if (mdnsfd < 0 || mdnsfd >= FD_SETSIZE) {
+			errno = EBADF;
+			break;
+		}
+
 		fdsetsz = howmany(mdnsfd + 1, NFDBITS) * sizeof(fd_mask);
 		fdset = TALLOC_ZERO(ctx, fdsetsz);
 		FD_SET(mdnsfd, fdset);
@@ -183,6 +188,13 @@ int do_smb_browse(void)
 
 		fdsetsz = howmany(mdnsfd + 1, NFDBITS) * sizeof(fd_mask);
 		fdset = TALLOC_ZERO(ctx, fdsetsz);
+
+		if (mdnsfd < 0 || mdnsfd >= FD_SETSIZE) {
+			errno = EBADF;
+			TALLOC_FREE(ctx);
+			return 1;
+		}
+
 		FD_SET(mdnsfd, fdset);
 
 		tv.tv_sec = 1;
diff --git a/source/lib/events.c b/source/lib/events.c
index cd20ceb..2ddbab7 100644
--- a/source/lib/events.c
+++ b/source/lib/events.c
@@ -140,6 +140,11 @@ struct fd_event *event_add_fd(struct event_context *event_ctx,
 {
 	struct fd_event *fde;
 
+	if (fd < 0 || fd >= FD_SETSIZE) {
+		errno = EBADF;
+		return NULL;
+	}
+
 	if (!(fde = TALLOC_P(mem_ctx, struct fd_event))) {
 		return NULL;
 	}
@@ -190,6 +195,14 @@ bool event_add_to_select_args(struct event_context *event_ctx,
 	bool ret = False;
 
 	for (fde = event_ctx->fd_events; fde; fde = fde->next) {
+		if (fde->fd < 0 || fde->fd >= FD_SETSIZE) {
+			/* We ignore here, as it shouldn't be
+			   possible to add an invalid fde->fd
+			   but we don't want FD_SET to see an
+			   invalid fd. */
+			continue;
+		}
+
 		if (fde->flags & EVENT_FD_READ) {
 			FD_SET(fde->fd, read_fds);
 			ret = True;
diff --git a/source/lib/packet.c b/source/lib/packet.c
index e048616..512c7f2 100644
--- a/source/lib/packet.c
+++ b/source/lib/packet.c
@@ -106,6 +106,11 @@ NTSTATUS packet_fd_read_sync(struct packet_context *ctx)
 	int res;
 	fd_set r_fds;
 
+	if (ctx->fd < 0 || ctx->fd >= FD_SETSIZE) {
+		errno = EBADF;
+		return map_nt_error_from_unix(errno);
+	}
+
 	FD_ZERO(&r_fds);
 	FD_SET(ctx->fd, &r_fds);
 
diff --git a/source/lib/readline.c b/source/lib/readline.c
index 34867aa..70a82f2 100644
--- a/source/lib/readline.c
+++ b/source/lib/readline.c
@@ -91,6 +91,11 @@ static char *smb_readline_replacement(const char *prompt, void (*callback)(void)
 		timeout.tv_sec = 5;
 		timeout.tv_usec = 0;
 
+		if (fd < 0 || fd >= FD_SETSIZE) {
+			errno = EBADF;
+			break;
+		}
+
 		FD_ZERO(&fds);
 		FD_SET(fd,&fds);
 
diff --git a/source/lib/select.c b/source/lib/select.c
index c3da6a9..2d5f02c 100644
--- a/source/lib/select.c
+++ b/source/lib/select.c
@@ -61,6 +61,11 @@ int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, s
 		if (pipe(select_pipe) == -1)
 			smb_panic("Could not create select pipe");
 
+		if (select_pipe[0] < 0 || select_pipe[0] >= FD_SETSIZE) {
+			errno = EBADF;
+			return -1;
+		}
+
 		/*
 		 * These next two lines seem to fix a bug with the Linux
 		 * 2.0.x kernel (and probably other UNIXes as well) where
@@ -87,6 +92,7 @@ int sys_select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *errorfds, s
 		readfds2 = &readfds_buf;
 		FD_ZERO(readfds2);
 	}
+
 	FD_SET(select_pipe[0], readfds2);
 
 	errno = 0;
diff --git a/source/lib/util_sock.c b/source/lib/util_sock.c
index 650bd13..8aa2c97 100644
--- a/source/lib/util_sock.c
+++ b/source/lib/util_sock.c
@@ -960,6 +960,11 @@ NTSTATUS read_socket_with_timeout(int fd, char *buf,
 	timeout.tv_usec = (long)(1000 * (time_out % 1000));
 
 	for (nread=0; nread < mincnt; ) {
+		if (fd < 0 || fd >= FD_SETSIZE) {
+			errno = EBADF;
+			return map_nt_error_from_unix(EBADF);
+		}
+
 		FD_ZERO(&fds);
 		FD_SET(fd,&fds);
 
@@ -1492,7 +1497,7 @@ bool open_any_socket_out(struct sockaddr_storage *addrs, int num_addrs,
 
 	for (i=0; i<num_addrs; i++) {
 		sockets[i] = socket(addrs[i].ss_family, SOCK_STREAM, 0);
-		if (sockets[i] < 0)
+		if (sockets[i] < 0 || sockets[i] >= FD_SETSIZE)
 			goto done;
 		set_blocking(sockets[i], false);
 	}
@@ -1541,8 +1546,10 @@ bool open_any_socket_out(struct sockaddr_storage *addrs, int num_addrs,
 	FD_ZERO(&r_fds);
 
 	for (i=0; i<num_addrs; i++) {
-		if (sockets[i] == -1)
+		if (sockets[i] < 0 || sockets[i] >= FD_SETSIZE) {
+			/* This cannot happen - ignore if so. */
 			continue;
+		}
 		FD_SET(sockets[i], &wr_fds);
 		FD_SET(sockets[i], &r_fds);
 		if (sockets[i]>maxfd)
diff --git a/source/libaddns/dnssock.c b/source/libaddns/dnssock.c
index 7c8bd41..f427bd5 100644
--- a/source/libaddns/dnssock.c
+++ b/source/libaddns/dnssock.c
@@ -218,7 +218,11 @@ static DNS_ERROR read_all(int fd, uint8 *data, size_t len)
 	while (total < len) {
 		ssize_t ret;
 		int fd_ready;
-		
+
+		if (fd < 0 || fd >= FD_SETSIZE) {
+			return ERROR_DNS_SOCKET_ERROR;
+		}
+
 		FD_ZERO( &rfds );
 		FD_SET( fd, &rfds );
 
diff --git a/source/libsmb/nmblib.c b/source/libsmb/nmblib.c
index bfe5e7b..768e54d 100644
--- a/source/libsmb/nmblib.c
+++ b/source/libsmb/nmblib.c
@@ -1097,6 +1097,11 @@ struct packet_struct *receive_packet(int fd,enum packet_type type,int t)
 	struct timeval timeout;
 	int ret;
 
+	if (fd < 0 || fd >= FD_SETSIZE) {
+		errno = EBADF;
+		return NULL;
+	}
+
 	FD_ZERO(&fds);
 	FD_SET(fd,&fds);
 	timeout.tv_sec = t/1000;
diff --git a/source/nmbd/nmbd_packets.c b/source/nmbd/nmbd_packets.c
index 4b97819..03e5362 100644
--- a/source/nmbd/nmbd_packets.c
+++ b/source/nmbd/nmbd_packets.c
@@ -1683,7 +1683,7 @@ static bool create_listen_fdset(fd_set **ppset, int **psock_array, int *listen_n
 	for (subrec = FIRST_SUBNET; subrec; subrec = NEXT_SUBNET_EXCLUDING_UNICAST(subrec))
 		count++;
 
-	if((count*2) + 2 > FD_SETSIZE) {
+	if((count*2) + 2 >= FD_SETSIZE) {
 		DEBUG(0,("create_listen_fdset: Too many file descriptors needed (%d). We can \
 only use %d.\n", (count*2) + 2, FD_SETSIZE));
 		SAFE_FREE(pset);
@@ -1699,24 +1699,44 @@ only use %d.\n", (count*2) + 2, FD_SETSIZE));
 	FD_ZERO(pset);
 
 	/* Add in the broadcast socket on 137. */
+	if (ClientNMB < 0 || ClientNMB >= FD_SETSIZE) {
+		errno = EBADF;
+		SAFE_FREE(pset);
+		return True;
+	}
+
 	FD_SET(ClientNMB,pset);
 	sock_array[num++] = ClientNMB;
 	*maxfd = MAX( *maxfd, ClientNMB);
 
 	/* Add in the 137 sockets on all the interfaces. */
 	for (subrec = FIRST_SUBNET; subrec; subrec = NEXT_SUBNET_EXCLUDING_UNICAST(subrec)) {
+		if (subrec->nmb_sock < 0 || subrec->nmb_sock >= FD_SETSIZE) {
+			/* We have to ignore sockets outside FD_SETSIZE. */
+			continue;
+		}
 		FD_SET(subrec->nmb_sock,pset);
 		sock_array[num++] = subrec->nmb_sock;
 		*maxfd = MAX( *maxfd, subrec->nmb_sock);
 	}
 
 	/* Add in the broadcast socket on 138. */
+	if (ClientDGRAM < 0 || ClientDGRAM >= FD_SETSIZE) {
+		errno = EBADF;
+		SAFE_FREE(pset);
+		return True;
+	}
+
 	FD_SET(ClientDGRAM,pset);
 	sock_array[num++] = ClientDGRAM;
 	*maxfd = MAX( *maxfd, ClientDGRAM);
 
 	/* Add in the 138 sockets on all the interfaces. */
 	for (subrec = FIRST_SUBNET; subrec; subrec = NEXT_SUBNET_EXCLUDING_UNICAST(subrec)) {
+		if (subrec->dgram_sock < 0 || subrec->dgram_sock >= FD_SETSIZE) {
+			/* We have to ignore sockets outside FD_SETSIZE. */
+			continue;
+		}
 		FD_SET(subrec->dgram_sock,pset);
 		sock_array[num++] = subrec->dgram_sock;
 		*maxfd = MAX( *maxfd, subrec->dgram_sock);
@@ -1767,7 +1787,7 @@ bool listen_for_packets(bool run_election)
 
 #ifndef SYNC_DNS
 	dns_fd = asyncdns_fd();
-	if (dns_fd != -1) {
+	if (dns_fd >= 0 && dns_fd < FD_SETSIZE) {
 		FD_SET(dns_fd, &r_fds);
 		maxfd = MAX( maxfd, dns_fd);
 	}
diff --git a/source/nsswitch/wb_common.c b/source/nsswitch/wb_common.c
index a164621..4f76bd0 100644
--- a/source/nsswitch/wb_common.c
+++ b/source/nsswitch/wb_common.c
@@ -240,6 +240,12 @@ static int winbind_named_pipe_sock(const char *dir)
 
 		switch (errno) {
 			case EINPROGRESS:
+
+				if (fd < 0 || fd >= FD_SETSIZE) {
+					errno = EBADF;
+					goto error_out;
+				}
+
 				FD_ZERO(&w_fds);
 				FD_SET(fd, &w_fds);
 				tv.tv_sec = CONNECT_TIMEOUT - wait_time;
@@ -383,7 +389,13 @@ int winbind_write_sock(void *buffer, int count, int recursing, int need_priv)
 	while(nwritten < count) {
 		struct timeval tv;
 		fd_set r_fds;
-		
+
+		if (winbindd_fd < 0 || winbindd_fd >= FD_SETSIZE) {
+			errno = EBADF;
+			winbind_close_sock();
+			return -1;
+		}
+
 		/* Catch pipe close on other end by checking if a read()
 		   call would not block by calling select(). */
 
@@ -443,7 +455,13 @@ int winbind_read_sock(void *buffer, int count)
 	while(nread < count) {
 		struct timeval tv;
 		fd_set r_fds;
-		
+
+		if (winbindd_fd < 0 || winbindd_fd >= FD_SETSIZE) {
+			errno = EBADF;
+			winbind_close_sock();
+			return -1;
+		}
+
 		/* Catch pipe close on other end by checking if a read()
 		   call would not block by calling select(). */
 
diff --git a/source/printing/printing.c b/source/printing/printing.c
index a9272eb..c3b8c61 100644
--- a/source/printing/printing.c
+++ b/source/printing/printing.c
@@ -1407,6 +1407,11 @@ void start_background_queue(void)
 		exit(1);
 	}
 
+	if (pause_pipe[1] < 0 || pause_pipe[1] >= FD_SETSIZE) {
+		DEBUG(5,("start_background_queue: pipe fd out of range.\n"));
+		exit(1);
+	}
+
 	background_lpq_updater_pid = sys_fork();
 
 	if (background_lpq_updater_pid == -1) {
diff --git a/source/smbd/dnsregister.c b/source/smbd/dnsregister.c
index f02739e..3c689b9 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();
diff --git a/source/smbd/oplock.c b/source/smbd/oplock.c
index a07d05d..5ae3fdf 100644
--- a/source/smbd/oplock.c
+++ b/source/smbd/oplock.c
@@ -241,7 +241,10 @@ bool downgrade_oplock(files_struct *fsp)
 int oplock_notify_fd(void)
 {
 	if (koplocks) {
-		return koplocks->notification_fd;
+		int fd = koplocks->notification_fd;
+		if (fd < 0 || fd >= FD_SETSIZE) {
+			return -1;
+		}
 	}
 
 	return -1;
diff --git a/source/smbd/oplock_irix.c b/source/smbd/oplock_irix.c
index 8c287c9..6e86fac 100644
--- a/source/smbd/oplock_irix.c
+++ b/source/smbd/oplock_irix.c
@@ -284,6 +284,11 @@ struct kernel_oplocks *irix_init_kernel_oplocks(void)
 		return False;
 	}
 
+	if (pfd[0] < 0 || pfd[0] >= FD_SETSIZE) {
+		DEBUG(0,("setup_kernel_oplock_pipe: fd out of range.\n"));
+		return False;
+	}
+
 	oplock_pipe_read = pfd[0];
 	oplock_pipe_write = pfd[1];
 
diff --git a/source/smbd/process.c b/source/smbd/process.c
index 403c7c6..9b8f29b 100644
--- a/source/smbd/process.c
+++ b/source/smbd/process.c
@@ -698,7 +698,7 @@ static void async_processing(fd_set *pfds)
 
 static int select_on_fd(int fd, int maxfd, fd_set *fds)
 {
-	if (fd != -1) {
+	if (fd != -1 && fd < FD_SETSIZE) {
 		FD_SET(fd, fds);
 		maxfd = MAX(maxfd, fd);
 	}
diff --git a/source/smbd/server.c b/source/smbd/server.c
index 5129484..a670334 100644
--- a/source/smbd/server.c
+++ b/source/smbd/server.c
@@ -209,7 +209,13 @@ static bool open_sockets_inetd(void)
 	/* Started from inetd. fd 0 is the socket. */
 	/* We will abort gracefully when the client or remote system 
 	   goes away */
-	smbd_set_server_fd(dup(0));
+	int fd = dup(0);
+
+	if (fd < 0 || fd >= FD_SETSIZE) {
+		return false;
+	}
+
+	smbd_set_server_fd(fd);
 	
 	/* close our standard file descriptors */
 	close_low_fds(False); /* Don't close stderr */
@@ -436,7 +442,8 @@ static bool open_sockets_smbd(bool is_daemon, bool interactive, const char *smb_
 							num_sockets == 0 ? 0 : 2,
 							ifss,
 							true);
-				if(s == -1) {
+				if(s < 0 || s >= FD_SETSIZE) {
+					close(s);
 					continue;
 				}
 
@@ -516,7 +523,7 @@ static bool open_sockets_smbd(bool is_daemon, bool interactive, const char *smb_
 						num_sockets == 0 ? 0 : 2,
 						&ss,
 						true);
-				if (s == -1) {
+				if (s < 0 || s >= FD_SETSIZE) {
 					continue;
 				}
 
@@ -709,6 +716,7 @@ static bool open_sockets_smbd(bool is_daemon, bool interactive, const char *smb_
 			struct sockaddr addr;
 			socklen_t in_addrlen = sizeof(addr);
 			pid_t child = 0;
+			int fd;
 
 			s = -1;
 			for(i = 0; i < num_sockets; i++) {
@@ -721,16 +729,21 @@ static bool open_sockets_smbd(bool is_daemon, bool interactive, const char *smb_
 				}
 			}
 
-			smbd_set_server_fd(accept(s,&addr,&in_addrlen));
-
-			if (smbd_server_fd() == -1 && errno == EINTR)
+			fd = accept(s,&addr,&in_addrlen);
+			if (fd == -1 && errno == EINTR)
 				continue;
-
-			if (smbd_server_fd() == -1) {
+			if (fd == -1) {
 				DEBUG(2,("open_sockets_smbd: accept: %s\n",
 					 strerror(errno)));
 				continue;
 			}
+			if (fd < 0 || fd >= FD_SETSIZE) {
+				DEBUG(2,("open_sockets_smbd: bad fd %d\n",
+					fd ));
+				continue;
+			}
+
+			smbd_set_server_fd(fd);
 
 			/* Ensure child is set to blocking mode */
 			set_blocking(smbd_server_fd(),True);
diff --git a/source/utils/smbfilter.c b/source/utils/smbfilter.c
index 1e22a40..45f9207 100644
--- a/source/utils/smbfilter.c
+++ b/source/utils/smbfilter.c
@@ -162,8 +162,8 @@ static void filter_child(int c, struct sockaddr_storage *dest_ss)
 		int num;
 		
 		FD_ZERO(&fds);
-		if (s != -1) FD_SET(s, &fds);
-		if (c != -1) FD_SET(c, &fds);
+		if (s >= 0 && s < FD_SETSIZE) FD_SET(s, &fds);
+		if (c >= 0 && c < FD_SETSIZE) FD_SET(c, &fds);
 
 		num = sys_select_intr(MAX(s+1, c+1),&fds,NULL,NULL,NULL);
 		if (num <= 0) continue;
@@ -235,6 +235,10 @@ static void start_filter(char *desthost)
 		struct sockaddr_storage ss;
 		socklen_t in_addrlen = sizeof(ss);
 		
+		if (s < 0 || s >= FD_SETSIZE) {
+			break;
+		}
+
 		FD_ZERO(&fds);
 		FD_SET(s, &fds);
 
diff --git a/source/winbindd/winbindd.c b/source/winbindd/winbindd.c
index 1d618e2..6b5c251 100644
--- a/source/winbindd/winbindd.c
+++ b/source/winbindd/winbindd.c
@@ -836,7 +836,8 @@ static void process_loop(void)
 	listen_sock = open_winbindd_socket();
 	listen_priv_sock = open_winbindd_priv_socket();
 
-	if (listen_sock == -1 || listen_priv_sock == -1) {
+	if (listen_sock < 0 || listen_sock >= FD_SETSIZE ||
+			listen_priv_sock < 0 || listen_priv_sock >= FD_SETSIZE) {
 		perror("open_winbind_socket");
 		exit(1);
 	}
@@ -861,6 +862,9 @@ static void process_loop(void)
 
 	FD_ZERO(&r_fds);
 	FD_ZERO(&w_fds);
+
+	/* We check the range for listen_sock and
+	   listen_priv_sock above. */
 	FD_SET(listen_sock, &r_fds);
 	FD_SET(listen_priv_sock, &r_fds);
 
@@ -890,6 +894,12 @@ static void process_loop(void)
 	}
 
 	for (ev = fd_events; ev; ev = ev->next) {
+		if (ev->fd < 0 || ev->fd >= FD_SETSIZE) {
+			/* Ignore here - event_add_to_select_args
+			   should make this impossible. */
+			continue;
+		}
+
 		if (ev->flags & EVENT_FD_READ) {
 			FD_SET(ev->fd, &r_fds);
 			maxfd = MAX(ev->fd, maxfd);
diff --git a/source/winbindd/winbindd_dual.c b/source/winbindd/winbindd_dual.c
index ff004f2..b30ec20 100644
--- a/source/winbindd/winbindd_dual.c
+++ b/source/winbindd/winbindd_dual.c
@@ -1250,6 +1250,12 @@ static bool fork_domain_child(struct winbindd_child *child)
 		return False;
 	}
 
+	if (fdpair[0] < 0 || fdpair[0] >= FD_SETSIZE) {
+		DEBUG(0, ("fork_domain_child: bad fd range (%d)\n", fdpair[0]));
+		errno = EBADF;
+		return False;
+	}
+
 	ZERO_STRUCT(state);
 	state.pid = sys_getpid();
 
@@ -1405,6 +1411,7 @@ static bool fork_domain_child(struct winbindd_child *child)
 		message_dispatch(winbind_messaging_context());
 
 		FD_ZERO(&read_fds);
+		/* We check state.sock against FD_SETSIZE above. */
 		FD_SET(state.sock, &read_fds);
 
 		ret = sys_select(state.sock + 1, &read_fds, NULL, NULL, tp);
-- 
1.6.4.2