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.

2 files changed, 15 insertions, 0 deletions

diff --git a/lib/tevent/tevent_select.c b/lib/tevent/tevent_select.c
index d97418991ae..890e0311c60 100644
--- a/lib/tevent/tevent_select.c
+++ b/lib/tevent/tevent_select.c
@@ -111,6 +111,11 @@ static struct tevent_fd *select_event_add_fd(struct tevent_context *ev, TALLOC_C
 							   struct select_event_context);
 	struct tevent_fd *fde;
 
+	if (fd < 0 || fd >= FD_SETSIZE) {
+		errno = EBADF;
+		return NULL;
+	}
+
 	fde = tevent_common_add_fd(ev, mem_ctx, fd, flags,
 				   handler, private_data,
 				   handler_name, location);
@@ -143,6 +148,11 @@ static int select_event_loop_select(struct select_event_context *select_ev, stru
 
 	/* setup any fd events */
 	for (fde = select_ev->ev->fd_events; fde; fde = fde->next) {
+		if (fde->fd < 0 || fde->fd >= FD_SETSIZE) {
+			errno = EBADF;
+			return -1;
+		}
+
 		if (fde->flags & TEVENT_FD_READ) {
 			FD_SET(fde->fd, &r_fds);
 		}
diff --git a/lib/tevent/tevent_standard.c b/lib/tevent/tevent_standard.c
index c3f8b36e840..d4a00cc062a 100644
--- a/lib/tevent/tevent_standard.c
+++ b/lib/tevent/tevent_standard.c
@@ -457,6 +457,11 @@ static int std_event_loop_select(struct std_event_context *std_ev, struct timeva
 
 	/* setup any fd events */
 	for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
+		if (fde->fd < 0 || fde->fd >= FD_SETSIZE) {
+			std_ev->exit_code = EBADF;
+			return -1;
+		}
+
 		if (fde->flags & TEVENT_FD_READ) {
 			FD_SET(fde->fd, &r_fds);
 		}