[PATCH] tty: ->signal->tty locking

Fix the locking of signal->tty.

Use ->sighand->siglock to protect ->signal->tty; this lock is already used
by most other members of ->signal/->sighand.  And unless we are 'current'
or the tasklist_lock is held we need ->siglock to access ->signal anyway.

(NOTE: sys_unshare() is broken wrt ->sighand locking rules)

Note that tty_mutex is held over tty destruction, so while holding
tty_mutex any tty pointer remains valid.  Otherwise the lifetime of ttys
are governed by their open file handles.  This leaves some holes for tty
access from signal->tty (or any other non file related tty access).

It solves the tty SLAB scribbles we were seeing.

(NOTE: the change from group_send_sig_info to __group_send_sig_info needs to
       be examined by someone familiar with the security framework, I think
       it is safe given the SEND_SIG_PRIV from other __group_send_sig_info
       invocations)

[schwidefsky@de.ibm.com: 3270 fix]
[akpm@osdl.org: various post-viro fixes]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Alan Cox <alan@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Jan Kara <jack@ucw.cz>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 44e9cd4..f5df8c7 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1695,9 +1695,10 @@ static inline void flush_unauthorized_files(struct files_struct * files)
 	struct tty_struct *tty;
 	struct fdtable *fdt;
 	long j = -1;
+	int drop_tty = 0;
 
 	mutex_lock(&tty_mutex);
-	tty = current->signal->tty;
+	tty = get_current_tty();
 	if (tty) {
 		file_list_lock();
 		file = list_entry(tty->tty_files.next, typeof(*file), f_u.fu_list);
@@ -1710,12 +1711,14 @@ static inline void flush_unauthorized_files(struct files_struct * files)
 			struct inode *inode = file->f_dentry->d_inode;
 			if (inode_has_perm(current, inode,
 					   FILE__READ | FILE__WRITE, NULL)) {
-				/* Reset controlling tty. */
-				current->signal->tty = NULL;
-				current->signal->tty_old_pgrp = 0;
+				drop_tty = 1;
 			}
 		}
 		file_list_unlock();
+
+		/* Reset controlling tty. */
+		if (drop_tty)
+			proc_set_tty(current, NULL);
 	}
 	mutex_unlock(&tty_mutex);