[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>

arch/sparc64/solaris/misc.c

@@ -423,9 +423,7 @@ asmlinkage int solaris_procids(int cmd, s32 pid, s32 pgid)
 			   Solaris setpgrp and setsid? */
 			ret = sys_setpgid(0, 0);
 			if (ret) return ret;
-			mutex_lock(&tty_mutex);
-			current->signal->tty = NULL;
-			mutex_unlock(&tty_mutex);
+			proc_clear_tty(current);
 			return process_group(current);
 		}
 	case 2: /* getsid */

arch/um/kernel/exec.c

@@ -39,12 +39,13 @@ static long execve1(char *file, char __user * __user *argv,
 		    char __user *__user *env)
 {
         long error;
+	struct tty_struct *tty;
 
 #ifdef CONFIG_TTY_LOG
 	mutex_lock(&tty_mutex);
-	task_lock(current);	/* FIXME:  is this needed ? */
-	log_exec(argv, current->signal->tty);
-	task_unlock(current);
+	tty = get_current_tty();
+	if (tty)
+		log_exec(argv, tty);
 	mutex_unlock(&tty_mutex);
 #endif
         error = do_execve(file, argv, env, &current->thread.regs);

drivers/s390/char/fs3270.c

@@ -424,11 +424,15 @@ fs3270_open(struct inode *inode, struct file *filp)
 	minor = iminor(filp->f_dentry->d_inode);
 	/* Check for minor 0 multiplexer. */
 	if (minor == 0) {
-		if (!current->signal->tty)
+		struct tty_struct *tty;
+		mutex_lock(&tty_mutex);
+		tty = get_current_tty();
+		if (!tty || tty->driver->major != IBM_TTY3270_MAJOR) {
+			mutex_unlock(&tty_mutex);
 			return -ENODEV;
-		if (current->signal->tty->driver->major != IBM_TTY3270_MAJOR)
-			return -ENODEV;
-		minor = current->signal->tty->index + RAW3270_FIRSTMINOR;
+		}
+		minor = tty->index + RAW3270_FIRSTMINOR;
+		mutex_unlock(&tty_mutex);
 	}
 	/* Check if some other program is already using fullscreen mode. */
 	fp = (struct fs3270 *) raw3270_find_view(&fs3270_fn, minor);

fs/dquot.c

@@ -828,6 +828,7 @@ static inline int need_print_warning(struct dquot *dquot)
 static void print_warning(struct dquot *dquot, const char warntype)
 {
 	char *msg = NULL;
+	struct tty_struct *tty;
 	int flag = (warntype == BHARDWARN || warntype == BSOFTLONGWARN) ? DQ_BLKS_B :
 	  ((warntype == IHARDWARN || warntype == ISOFTLONGWARN) ? DQ_INODES_B : 0);
 
@@ -835,14 +836,15 @@ static void print_warning(struct dquot *dquot, const char warntype)
 		return;
 
 	mutex_lock(&tty_mutex);
-	if (!current->signal->tty)
+	tty = get_current_tty();
+	if (!tty)
 		goto out_lock;
-	tty_write_message(current->signal->tty, dquot->dq_sb->s_id);
+	tty_write_message(tty, dquot->dq_sb->s_id);
 	if (warntype == ISOFTWARN || warntype == BSOFTWARN)
-		tty_write_message(current->signal->tty, ": warning, ");
+		tty_write_message(tty, ": warning, ");
 	else
-		tty_write_message(current->signal->tty, ": write failed, ");
-	tty_write_message(current->signal->tty, quotatypes[dquot->dq_type]);
+		tty_write_message(tty, ": write failed, ");
+	tty_write_message(tty, quotatypes[dquot->dq_type]);
 	switch (warntype) {
 		case IHARDWARN:
 			msg = " file limit reached.\r\n";
@@ -863,7 +865,7 @@ static void print_warning(struct dquot *dquot, const char warntype)
 			msg = " block quota exceeded.\r\n";
 			break;
 	}
-	tty_write_message(current->signal->tty, msg);
+	tty_write_message(tty, msg);
 out_lock:
 	mutex_unlock(&tty_mutex);
 }

fs/open.c

@@ -1087,6 +1087,7 @@ EXPORT_SYMBOL(sys_close);
 asmlinkage long sys_vhangup(void)
 {
 	if (capable(CAP_SYS_TTY_CONFIG)) {
+		/* XXX: this needs locking */
 		tty_vhangup(current->signal->tty);
 		return 0;
 	}

include/linux/tty.h

@@ -309,6 +309,12 @@ extern void tty_ldisc_flush(struct tty_struct *tty);
 extern int tty_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
 		     unsigned long arg);
 
+extern dev_t tty_devnum(struct tty_struct *tty);
+extern void proc_clear_tty(struct task_struct *p);
+extern void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
+extern void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
+extern struct tty_struct *get_current_tty(void);
+
 extern struct mutex tty_mutex;
 
 /* n_tty.c */
@@ -335,10 +341,5 @@ extern void console_print(const char *);
 extern int vt_ioctl(struct tty_struct *tty, struct file * file,
 		    unsigned int cmd, unsigned long arg);
 
-static inline dev_t tty_devnum(struct tty_struct *tty)
-{
-	return MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
-}
-
 #endif /* __KERNEL__ */
 #endif

kernel/acct.c

@@ -428,6 +428,7 @@ static void do_acct_process(struct file *file)
 	u64 elapsed;
 	u64 run_time;
 	struct timespec uptime;
+	struct tty_struct *tty;
 
 	/*
 	 * First check to see if there is enough free_space to continue
@@ -485,12 +486,8 @@ static void do_acct_process(struct file *file)
 #endif
 
 	mutex_lock(&tty_mutex);
-	/* FIXME: Whoever is responsible for current->signal locking needs
-	   to use the same locking all over the kernel and document it */
-	read_lock(&tasklist_lock);
-	ac.ac_tty = current->signal->tty ?
-		old_encode_dev(tty_devnum(current->signal->tty)) : 0;
-	read_unlock(&tasklist_lock);
+	tty = get_current_tty();
+	ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
 	mutex_unlock(&tty_mutex);
 
 	spin_lock_irq(&current->sighand->siglock);

kernel/auditsc.c

@@ -826,10 +826,12 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 				 context->return_code);
 
 	mutex_lock(&tty_mutex);
+	read_lock(&tasklist_lock);
 	if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
 		tty = tsk->signal->tty->name;
 	else
 		tty = "(none)";
+	read_unlock(&tasklist_lock);
 	audit_log_format(ab,
 		  " a0=%lx a1=%lx a2=%lx a3=%lx items=%d"
 		  " ppid=%d pid=%d auid=%u uid=%u gid=%u"

kernel/exit.c

@@ -384,9 +384,7 @@ void daemonize(const char *name, ...)
 	exit_mm(current);
 
 	set_special_pids(1, 1);
-	mutex_lock(&tty_mutex);
-	current->signal->tty = NULL;
-	mutex_unlock(&tty_mutex);
+	proc_clear_tty(current);
 
 	/* Block and flush all signals */
 	sigfillset(&blocked);

kernel/sys.c

@@ -1484,7 +1484,6 @@ asmlinkage long sys_setsid(void)
 	pid_t session;
 	int err = -EPERM;
 
-	mutex_lock(&tty_mutex);
 	write_lock_irq(&tasklist_lock);
 
 	/* Fail if I am already a session leader */
@@ -1504,12 +1503,15 @@ asmlinkage long sys_setsid(void)
 
 	group_leader->signal->leader = 1;
 	__set_special_pids(session, session);
+
+	spin_lock(&group_leader->sighand->siglock);
 	group_leader->signal->tty = NULL;
 	group_leader->signal->tty_old_pgrp = 0;
+	spin_unlock(&group_leader->sighand->siglock);
+
 	err = process_group(group_leader);
 out:
 	write_unlock_irq(&tasklist_lock);
-	mutex_unlock(&tty_mutex);
 	return err;
 }
 

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);