[PATCH] SELinux: revalidate access to controlling tty

This patch changes the SELinux flush_unauthorized_files function to also
recheck access to the controlling tty and reset it if it is no longer
accessible under the new security context.  This patch is relative to the
selinuxfs devnull patch.
Signed-off-by: Stephen Smalley <sds@epoch.ncsc.mil>
Signed-off-by: James Morris <jmorris@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

security/selinux/hooks.c

@@ -43,6 +43,7 @@
 #include <linux/kd.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/netfilter_ipv6.h>
+#include <linux/tty.h>
 #include <net/icmp.h>
 #include <net/ip.h>		/* for sysctl_local_port_range[] */
 #include <net/tcp.h>		/* struct or_callable used in sock_rcv_skb */
@@ -1733,8 +1734,32 @@ static inline void flush_unauthorized_files(struct files_struct * files)
 {
 	struct avc_audit_data ad;
 	struct file *file, *devnull = NULL;
+	struct tty_struct *tty = current->signal->tty;
 	long j = -1;
 
+	if (tty) {
+		file_list_lock();
+		file = list_entry(tty->tty_files.next, typeof(*file), f_list);
+		if (file) {
+			/* Revalidate access to controlling tty.
+			   Use inode_has_perm on the tty inode directly rather
+			   than using file_has_perm, as this particular open
+			   file may belong to another process and we are only
+			   interested in the inode-based check here. */
+			struct inode *inode = file->f_dentry->d_inode;
+			if (inode_has_perm(current, inode,
+					   FILE__READ | FILE__WRITE,
+					   NULL, NULL)) {
+				/* Reset controlling tty. */
+				current->signal->tty = NULL;
+				current->signal->tty_old_pgrp = 0;
+			}
+		}
+		file_list_unlock();
+	}
+
+	/* Revalidate access to inherited open files. */
+
 	AVC_AUDIT_DATA_INIT(&ad,FS);
 
 	spin_lock(&files->file_lock);