Date: Mon, 16 Oct 2006 15:40:43 +0200
From: Peter Zijlstra <pzijlstr@redhat.com>
Subject: Re: [RHEL5 PATCH 1/2 ]: BZ 210249 2.6.19 backport tty locking
	fixups

How about this roll-up

b20c8122a3204496fca8b5343c93b60fe11dad04 [PATCH] selinux: fix tty locking tty locking
0f0f1b400ce3c4780b9d974bc69e8b558d99aba4 [PATCH] Voyager: tty locking tty locking
b1fc0b1f21c4082d24d1f456a846b4fa7d16a70b [PATCH] UML: tty locking tty locking
fab2062ee4a3969a9c6cb7155534d0d15ddeff54 [PATCH] git-netdev-all: pc300_tty build fix build fix
51dced544e3964b684afc99282ceceaa384b16a8 [S390] init_timer in tty3270. in tty3270.
402749ea2538be9ddad981a990739b93a0178bc6 [PATCH] Remove unused tty_struct field tty_struct field
527063ba985740e9cd271731c31f503f916681c9 [PATCH] tty_io.c: keep davej sane davej sane
ca9bda00b4aafc42cd3d1b9d32934463e2993b4c [PATCH] tty locking on resize on resize
b525a7e4445c4702dfc541930747517615c0c72a [PATCH] dquot: add proper locking when using current->signal->tty using current->signal->tty
1266b1e1aed0a4d7d5cb569deca8c31cba34a990 [PATCH] tty: trivial kzalloc opportunity kzalloc opportunity
808a0d389ff8d85017ec811085a6083394c02caf [PATCH] tty: lock ticogwinsz lock ticogwinsz
3cfd0885fac78c130a119ed576d18b5948fa2a5a [PATCH] tty: stop the tty vanishing under procfs access procfs access
5785c95baede8459d70c4aa0f7becb6e8b5fde4b [PATCH] tty: make termios_sem a mutex a mutex
de2a84f2be8ed8a166f13d6aa2ae474541172bb2 [PATCH] solaris emulation: incorrect tty locking tty locking
28298232a15c48ea9835d5d24577cde87923e55c [PATCH] tty: Fix bits and note more bits to fix to fix
5f412b24240d92212e50ebbaff2dff20c9e6f3d0 [PATCH] Fix locking for tty drivers when doing urgent characters urgent characters
eb84a20e9e6b98dcb33023ad22241d79107a08a7 [PATCH] audit/accounting: tty locking tty locking


Index: linux-2.6.18.noarch/security/selinux/hooks.c
===================================================================
--- linux-2.6.18.noarch.orig/security/selinux/hooks.c
+++ linux-2.6.18.noarch/security/selinux/hooks.c
@@ -1705,10 +1705,12 @@ static inline void flush_unauthorized_fi
 {
 	struct avc_audit_data ad;
 	struct file *file, *devnull = NULL;
-	struct tty_struct *tty = current->signal->tty;
+	struct tty_struct *tty;
 	struct fdtable *fdt;
 	long j = -1;
 
+	mutex_lock(&tty_mutex);
+	tty = current->signal->tty;
 	if (tty) {
 		file_list_lock();
 		file = list_entry(tty->tty_files.next, typeof(*file), f_u.fu_list);
@@ -1728,6 +1730,7 @@ static inline void flush_unauthorized_fi
 		}
 		file_list_unlock();
 	}
+	mutex_unlock(&tty_mutex);
 
 	/* Revalidate access to inherited open files. */
 
Index: linux-2.6.18.noarch/arch/i386/mach-voyager/voyager_thread.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/i386/mach-voyager/voyager_thread.c
+++ linux-2.6.18.noarch/arch/i386/mach-voyager/voyager_thread.c
@@ -130,7 +130,6 @@ thread(void *unused)
 	init_timer(&wakeup_timer);
 
 	sigfillset(&current->blocked);
-	current->signal->tty = NULL;
 
 	printk(KERN_NOTICE "Voyager starting monitor thread\n");
 
Index: linux-2.6.18.noarch/arch/um/kernel/exec.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/um/kernel/exec.c
+++ linux-2.6.18.noarch/arch/um/kernel/exec.c
@@ -41,9 +41,11 @@ static long execve1(char *file, char __u
         long error;
 
 #ifdef CONFIG_TTY_LOG
-	task_lock(current);
+	mutex_lock(&tty_mutex);
+	task_lock(current);	/* FIXME:  is this needed ? */
 	log_exec(argv, current->signal->tty);
 	task_unlock(current);
+	mutex_unlock(&tty_mutex);
 #endif
         error = do_execve(file, argv, env, &current->thread.regs);
         if (error == 0){
Index: linux-2.6.18.noarch/drivers/net/wan/pc300.h
===================================================================
--- linux-2.6.18.noarch.orig/drivers/net/wan/pc300.h
+++ linux-2.6.18.noarch/drivers/net/wan/pc300.h
@@ -100,6 +100,7 @@
 #define	_PC300_H
 
 #include <linux/hdlc.h>
+#include <net/syncppp.h>
 #include "hd64572.h"
 #include "pc300-falc-lh.h"
 
Index: linux-2.6.18.noarch/drivers/s390/char/tty3270.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/s390/char/tty3270.c
+++ linux-2.6.18.noarch/drivers/s390/char/tty3270.c
@@ -698,7 +698,6 @@ tty3270_alloc_view(void)
 	if (!tp->freemem_pages)
 		goto out_tp;
 	INIT_LIST_HEAD(&tp->freemem);
-	init_timer(&tp->timer);
 	for (pages = 0; pages < TTY3270_STRING_PAGES; pages++) {
 		tp->freemem_pages[pages] = (void *)
 			__get_free_pages(GFP_KERNEL|GFP_DMA, 0);
Index: linux-2.6.18.noarch/include/linux/tty.h
===================================================================
--- linux-2.6.18.noarch.orig/include/linux/tty.h
+++ linux-2.6.18.noarch/include/linux/tty.h
@@ -174,7 +174,7 @@ struct tty_struct {
 	struct tty_driver *driver;
 	int index;
 	struct tty_ldisc ldisc;
-	struct semaphore termios_sem;
+	struct mutex termios_mutex;
 	struct termios *termios, *termios_locked;
 	char name[64];
 	int pgrp;
@@ -190,7 +190,6 @@ struct tty_struct {
 	struct tty_struct *link;
 	struct fasync_struct *fasync;
 	struct tty_bufhead buf;
-	int max_flip_cnt;
 	int alt_speed;		/* For magic substitution of 38400 bps */
 	wait_queue_head_t write_wait;
 	wait_queue_head_t read_wait;
Index: linux-2.6.18.noarch/drivers/char/tty_io.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/char/tty_io.c
+++ linux-2.6.18.noarch/drivers/char/tty_io.c
@@ -129,6 +129,7 @@ LIST_HEAD(tty_drivers);			/* linked list
 /* Semaphore to protect creating and releasing a tty. This is shared with
    vt.c for deeply disgusting hack reasons */
 DEFINE_MUTEX(tty_mutex);
+EXPORT_SYMBOL(tty_mutex);
 
 int console_use_vt = 1;
 
@@ -162,17 +163,11 @@ static void release_mem(struct tty_struc
  *	been initialized in any way but has been zeroed
  *
  *	Locking: none
- *	FIXME: use kzalloc
  */
 
 static struct tty_struct *alloc_tty_struct(void)
 {
-	struct tty_struct *tty;
-
-	tty = kmalloc(sizeof(struct tty_struct), GFP_KERNEL);
-	if (tty)
-		memset(tty, 0, sizeof(struct tty_struct));
-	return tty;
+	return kzalloc(sizeof(struct tty_struct), GFP_KERNEL);
 }
 
 static void tty_buffer_free_all(struct tty_struct *);
@@ -485,10 +480,9 @@ int tty_insert_flip_string(struct tty_st
 		tb->used += space;
 		copied += space;
 		chars += space;
-	}
-	/* There is a small chance that we need to split the data over
-	   several buffers. If this is the case we must loop */
-	while (unlikely(size > copied));
+		/* There is a small chance that we need to split the data over
+		   several buffers. If this is the case we must loop */
+	} while (unlikely(size > copied));
 	return copied;
 }
 EXPORT_SYMBOL(tty_insert_flip_string);
@@ -523,10 +517,9 @@ int tty_insert_flip_string_flags(struct 
 		copied += space;
 		chars += space;
 		flags += space;
-	}
-	/* There is a small chance that we need to split the data over
-	   several buffers. If this is the case we must loop */
-	while (unlikely(size > copied));
+		/* There is a small chance that we need to split the data over
+		   several buffers. If this is the case we must loop */
+	} while (unlikely(size > copied));
 	return copied;
 }
 EXPORT_SYMBOL(tty_insert_flip_string_flags);
@@ -628,9 +621,9 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_strin
  
 static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 {
-	down(&tty->termios_sem);
+	mutex_lock(&tty->termios_mutex);
 	tty->termios->c_line = num;
-	up(&tty->termios_sem);
+	mutex_unlock(&tty->termios_mutex);
 }
 
 /*
@@ -1348,9 +1341,9 @@ static void do_tty_hangup(void *data)
 	 */
 	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
 	{
-		down(&tty->termios_sem);
+		mutex_lock(&tty->termios_mutex);
 		*tty->termios = tty->driver->init_termios;
-		up(&tty->termios_sem);
+		mutex_unlock(&tty->termios_mutex);
 	}
 	
 	/* Defer ldisc switch */
@@ -2728,6 +2721,8 @@ static int tty_fasync(int fd, struct fil
  *	Locking:
  *		Called functions take tty_ldisc_lock
  *		current->signal->tty check is safe without locks
+ *
+ *	FIXME: may race normal receive processing
  */
 
 static int tiocsti(struct tty_struct *tty, char __user *p)
@@ -2750,18 +2745,21 @@ static int tiocsti(struct tty_struct *tt
  *	@tty; tty
  *	@arg: user buffer for result
  *
- *	Copies the kernel idea of the window size into the user buffer. No
- *	locking is done.
+ *	Copies the kernel idea of the window size into the user buffer.
  *
- *	FIXME: Returning random values racing a window size set is wrong
- *	should lock here against that
+ *	Locking: tty->termios_sem is taken to ensure the winsize data
+ *		is consistent.
  */
 
 static int tiocgwinsz(struct tty_struct *tty, struct winsize __user * arg)
 {
-	if (copy_to_user(arg, &tty->winsize, sizeof(*arg)))
-		return -EFAULT;
-	return 0;
+	int err;
+
+	mutex_lock(&tty->termios_mutex);
+	err = copy_to_user(arg, &tty->winsize, sizeof(*arg));
+	mutex_unlock(&tty->termios_mutex);
+
+	return err ? -EFAULT: 0;
 }
 
 /**
@@ -2774,12 +2772,11 @@ static int tiocgwinsz(struct tty_struct 
  *	actually has driver level meaning and triggers a VC resize.
  *
  *	Locking:
- *		The console_sem is used to ensure we do not try and resize
- *	the console twice at once.
- *	FIXME: Two racing size sets may leave the console and kernel
- *		parameters disagreeing. Is this exploitable ?
- *	FIXME: Random values racing a window size get is wrong
- *	should lock here against that
+ *		Called function use the console_sem is used to ensure we do
+ *	not try and resize the console twice at once.
+ *		The tty->termios_sem is used to ensure we don't double
+ *	resize and get confused. Lock order - tty->termios.sem before
+ *	console sem
  */
 
 static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty,
@@ -2789,17 +2786,18 @@ static int tiocswinsz(struct tty_struct 
 
 	if (copy_from_user(&tmp_ws, arg, sizeof(*arg)))
 		return -EFAULT;
+
+	mutex_lock(&tty->termios_mutex);
 	if (!memcmp(&tmp_ws, &tty->winsize, sizeof(*arg)))
-		return 0;
+		goto done;
+
 #ifdef CONFIG_VT
 	if (tty->driver->type == TTY_DRIVER_TYPE_CONSOLE) {
-		int rc;
-
-		acquire_console_sem();
-		rc = vc_resize(tty->driver_data, tmp_ws.ws_col, tmp_ws.ws_row);
-		release_console_sem();
-		if (rc)
-			return -ENXIO;
+		if (vc_lock_resize(tty->driver_data, tmp_ws.ws_col,
+					tmp_ws.ws_row)) {
+			mutex_unlock(&tty->termios_mutex);
+ 			return -ENXIO;
+		}
 	}
 #endif
 	if (tty->pgrp > 0)
@@ -2808,6 +2806,8 @@ static int tiocswinsz(struct tty_struct 
 		kill_pg(real_tty->pgrp, SIGWINCH, 1);
 	tty->winsize = tmp_ws;
 	real_tty->winsize = tmp_ws;
+done:
+	mutex_unlock(&tty->termios_mutex);
 	return 0;
 }
 
@@ -2882,9 +2882,7 @@ static int fionbio(struct file *file, in
  *	Locking:
  *		Takes tasklist lock internally to walk sessions
  *		Takes task_lock() when updating signal->tty
- *
- *	FIXME: tty_mutex is needed to protect signal->tty references.
- *	FIXME: why task_lock on the signal->tty reference ??
+ *		Takes tty_mutex() to protect tty instance
  *
  */
 
@@ -2919,9 +2917,11 @@ static int tiocsctty(struct tty_struct *
 		} else
 			return -EPERM;
 	}
+	mutex_lock(&tty_mutex);
 	task_lock(current);
 	current->signal->tty = tty;
 	task_unlock(current);
+	mutex_unlock(&tty_mutex);
 	current->signal->tty_old_pgrp = 0;
 	tty->session = current->signal->session;
 	tty->pgrp = process_group(current);
@@ -2961,8 +2961,6 @@ static int tiocgpgrp(struct tty_struct *
  *	permitted where the tty session is our session.
  *
  *	Locking: None
- *
- *	FIXME: current->signal->tty referencing is unsafe.
  */
 
 static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
@@ -3041,19 +3039,20 @@ static int tiocsetd(struct tty_struct *t
  *	timed break functionality.
  *
  *	Locking:
- *		None
+ *		atomic_write_lock serializes
  *
- *	FIXME:
- *		What if two overlap
  */
 
 static int send_break(struct tty_struct *tty, unsigned int duration)
 {
+	if (mutex_lock_interruptible(&tty->atomic_write_lock))
+		return -EINTR;
 	tty->driver->break_ctl(tty, -1);
 	if (!signal_pending(current)) {
 		msleep_interruptible(duration);
 	}
 	tty->driver->break_ctl(tty, 0);
+	mutex_unlock(&tty->atomic_write_lock);
 	if (signal_pending(current))
 		return -EINTR;
 	return 0;
@@ -3146,6 +3145,8 @@ int tty_ioctl(struct inode * inode, stru
 	if (tty_paranoia_check(tty, inode, "tty_ioctl"))
 		return -EINVAL;
 
+	/* CHECKME: is this safe as one end closes ? */
+
 	real_tty = tty;
 	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
 	    tty->driver->subtype == PTY_TYPE_MASTER)
@@ -3582,7 +3583,7 @@ static void initialize_tty_struct(struct
 	tty_buffer_init(tty);
 	INIT_WORK(&tty->buf.work, flush_to_ldisc, tty);
 	init_MUTEX(&tty->buf.pty_sem);
-	init_MUTEX(&tty->termios_sem);
+	mutex_init(&tty->termios_mutex);
 	init_waitqueue_head(&tty->write_wait);
 	init_waitqueue_head(&tty->read_wait);
 	INIT_WORK(&tty->hangup_work, do_tty_hangup, tty);
Index: linux-2.6.18.noarch/drivers/char/selection.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/char/selection.c
+++ linux-2.6.18.noarch/drivers/char/selection.c
@@ -33,7 +33,7 @@ extern void poke_blanked_console(void);
 
 /* Variables for selection control. */
 /* Use a dynamic buffer, instead of static (Dec 1994) */
-struct vc_data *sel_cons;		/* must not be disallocated */
+struct vc_data *sel_cons;		/* must not be deallocated */
 static volatile int sel_start = -1; 	/* cleared by clear_selection */
 static int sel_end;
 static int sel_buffer_lth;
Index: linux-2.6.18.noarch/drivers/char/vt.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/char/vt.c
+++ linux-2.6.18.noarch/drivers/char/vt.c
@@ -878,8 +878,17 @@ int vc_resize(struct vc_data *vc, unsign
 	return err;
 }
 
+int vc_lock_resize(struct vc_data *vc, unsigned int cols, unsigned int lines)
+{
+	int rc;
+
+	acquire_console_sem();
+	rc = vc_resize(vc, cols, lines);
+	release_console_sem();
+	return rc;
+}
 
-void vc_disallocate(unsigned int currcons)
+void vc_deallocate(unsigned int currcons)
 {
 	WARN_CONSOLE_UNLOCKED();
 
@@ -3765,6 +3774,7 @@ EXPORT_SYMBOL(default_blu);
 EXPORT_SYMBOL(update_region);
 EXPORT_SYMBOL(redraw_screen);
 EXPORT_SYMBOL(vc_resize);
+EXPORT_SYMBOL(vc_lock_resize);
 EXPORT_SYMBOL(fg_console);
 EXPORT_SYMBOL(console_blank_hook);
 EXPORT_SYMBOL(console_blanked);
Index: linux-2.6.18.noarch/drivers/char/vt_ioctl.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/char/vt_ioctl.c
+++ linux-2.6.18.noarch/drivers/char/vt_ioctl.c
@@ -96,7 +96,7 @@ do_kdsk_ioctl(int cmd, struct kbentry __
 		if (!perm)
 			return -EPERM;
 		if (!i && v == K_NOSUCHMAP) {
-			/* disallocate map */
+			/* deallocate map */
 			key_map = key_maps[s];
 			if (s && key_map) {
 			    key_maps[s] = NULL;
@@ -819,20 +819,20 @@ int vt_ioctl(struct tty_struct *tty, str
 		if (arg > MAX_NR_CONSOLES)
 			return -ENXIO;
 		if (arg == 0) {
-		    /* disallocate all unused consoles, but leave 0 */
+		    /* deallocate all unused consoles, but leave 0 */
 			acquire_console_sem();
 			for (i=1; i<MAX_NR_CONSOLES; i++)
 				if (! VT_BUSY(i))
-					vc_disallocate(i);
+					vc_deallocate(i);
 			release_console_sem();
 		} else {
-			/* disallocate a single console, if possible */
+			/* deallocate a single console, if possible */
 			arg--;
 			if (VT_BUSY(arg))
 				return -EBUSY;
 			if (arg) {			      /* leave 0 */
 				acquire_console_sem();
-				vc_disallocate(arg);
+				vc_deallocate(arg);
 				release_console_sem();
 			}
 		}
@@ -847,11 +847,8 @@ int vt_ioctl(struct tty_struct *tty, str
 		if (get_user(ll, &vtsizes->v_rows) ||
 		    get_user(cc, &vtsizes->v_cols))
 			return -EFAULT;
-		for (i = 0; i < MAX_NR_CONSOLES; i++) {
-			acquire_console_sem();
-			vc_resize(vc_cons[i].d, cc, ll);
-			release_console_sem();
-		}
+		for (i = 0; i < MAX_NR_CONSOLES; i++)
+			vc_lock_resize(vc_cons[i].d, cc, ll);
 		return 0;
 	}
 
Index: linux-2.6.18.noarch/include/linux/vt_kern.h
===================================================================
--- linux-2.6.18.noarch.orig/include/linux/vt_kern.h
+++ linux-2.6.18.noarch/include/linux/vt_kern.h
@@ -33,7 +33,8 @@ extern int fg_console, last_console, wan
 int vc_allocate(unsigned int console);
 int vc_cons_allocated(unsigned int console);
 int vc_resize(struct vc_data *vc, unsigned int cols, unsigned int lines);
-void vc_disallocate(unsigned int console);
+int vc_lock_resize(struct vc_data *vc, unsigned int cols, unsigned int lines);
+void vc_deallocate(unsigned int console);
 void reset_palette(struct vc_data *vc);
 void do_blank_screen(int entering_gfx);
 void do_unblank_screen(int leaving_gfx);
Index: linux-2.6.18.noarch/fs/dquot.c
===================================================================
--- linux-2.6.18.noarch.orig/fs/dquot.c
+++ linux-2.6.18.noarch/fs/dquot.c
@@ -834,6 +834,9 @@ static void print_warning(struct dquot *
 	if (!need_print_warning(dquot) || (flag && test_and_set_bit(flag, &dquot->dq_flags)))
 		return;
 
+	mutex_lock(&tty_mutex);
+	if (!current->signal->tty)
+		goto out_lock;
 	tty_write_message(current->signal->tty, dquot->dq_sb->s_id);
 	if (warntype == ISOFTWARN || warntype == BSOFTWARN)
 		tty_write_message(current->signal->tty, ": warning, ");
@@ -861,6 +864,8 @@ static void print_warning(struct dquot *
 			break;
 	}
 	tty_write_message(current->signal->tty, msg);
+out_lock:
+	mutex_unlock(&tty_mutex);
 }
 
 static inline void flush_warnings(struct dquot **dquots, char *warntype)
Index: linux-2.6.18.noarch/fs/proc/array.c
===================================================================
--- linux-2.6.18.noarch.orig/fs/proc/array.c
+++ linux-2.6.18.noarch/fs/proc/array.c
@@ -355,6 +355,8 @@ static int do_task_stat(struct task_stru
 	sigemptyset(&sigign);
 	sigemptyset(&sigcatch);
 	cutime = cstime = utime = stime = cputime_zero;
+
+	mutex_lock(&tty_mutex);
 	read_lock(&tasklist_lock);
 	if (task->sighand) {
 		spin_lock_irq(&task->sighand->siglock);
@@ -396,6 +398,7 @@ static int do_task_stat(struct task_stru
 	}
 	ppid = pid_alive(task) ? task->group_leader->parent->tgid : 0;
 	read_unlock(&tasklist_lock);
+	mutex_unlock(&tty_mutex);
 
 	if (!whole || num_threads<2) {
 		wchan = 0;
Index: linux-2.6.18.noarch/drivers/char/tty_ioctl.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/char/tty_ioctl.c
+++ linux-2.6.18.noarch/drivers/char/tty_ioctl.c
@@ -20,6 +20,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/bitops.h>
+#include <linux/mutex.h>
 
 #include <asm/io.h>
 #include <asm/uaccess.h>
@@ -131,7 +132,7 @@ static void change_termios(struct tty_st
 
 	/* FIXME: we need to decide on some locking/ordering semantics
 	   for the set_termios notification eventually */
-	down(&tty->termios_sem);
+	mutex_lock(&tty->termios_mutex);
 
 	*tty->termios = *new_termios;
 	unset_locked_termios(tty->termios, &old_termios, tty->termios_locked);
@@ -176,7 +177,7 @@ static void change_termios(struct tty_st
 			(ld->set_termios)(tty, &old_termios);
 		tty_ldisc_deref(ld);
 	}
-	up(&tty->termios_sem);
+	mutex_unlock(&tty->termios_mutex);
 }
 
 /**
@@ -284,13 +285,13 @@ static int get_sgttyb(struct tty_struct 
 {
 	struct sgttyb tmp;
 
-	down(&tty->termios_sem);
+	mutex_lock(&tty->termios_mutex);
 	tmp.sg_ispeed = 0;
 	tmp.sg_ospeed = 0;
 	tmp.sg_erase = tty->termios->c_cc[VERASE];
 	tmp.sg_kill = tty->termios->c_cc[VKILL];
 	tmp.sg_flags = get_sgflags(tty);
-	up(&tty->termios_sem);
+	mutex_unlock(&tty->termios_mutex);
 	
 	return copy_to_user(sgttyb, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
@@ -345,12 +346,12 @@ static int set_sgttyb(struct tty_struct 
 	if (copy_from_user(&tmp, sgttyb, sizeof(tmp)))
 		return -EFAULT;
 
-	down(&tty->termios_sem);		
+	mutex_lock(&tty->termios_mutex);
 	termios =  *tty->termios;
 	termios.c_cc[VERASE] = tmp.sg_erase;
 	termios.c_cc[VKILL] = tmp.sg_kill;
 	set_sgflags(&termios, tmp.sg_flags);
-	up(&tty->termios_sem);
+	mutex_unlock(&tty->termios_mutex);
 	change_termios(tty, &termios);
 	return 0;
 }
@@ -422,24 +423,28 @@ static int set_ltchars(struct tty_struct
  *
  *	Send a high priority character to the tty even if stopped
  *
- *	Locking: none
- *
- *	FIXME: overlapping calls with start/stop tty lose state of tty
+ *	Locking: none for xchar method, write ordering for write method.
  */
 
-static void send_prio_char(struct tty_struct *tty, char ch)
+static int send_prio_char(struct tty_struct *tty, char ch)
 {
 	int	was_stopped = tty->stopped;
 
 	if (tty->driver->send_xchar) {
 		tty->driver->send_xchar(tty, ch);
-		return;
+		return 0;
 	}
+
+	if (mutex_lock_interruptible(&tty->atomic_write_lock))
+		return -ERESTARTSYS;
+
 	if (was_stopped)
 		start_tty(tty);
 	tty->driver->write(tty, &ch, 1);
 	if (was_stopped)
 		stop_tty(tty);
+	mutex_unlock(&tty->atomic_write_lock);
+	return 0;
 }
 
 int n_tty_ioctl(struct tty_struct * tty, struct file * file,
@@ -513,11 +518,11 @@ int n_tty_ioctl(struct tty_struct * tty,
 				break;
 			case TCIOFF:
 				if (STOP_CHAR(tty) != __DISABLED_CHAR)
-					send_prio_char(tty, STOP_CHAR(tty));
+					return send_prio_char(tty, STOP_CHAR(tty));
 				break;
 			case TCION:
 				if (START_CHAR(tty) != __DISABLED_CHAR)
-					send_prio_char(tty, START_CHAR(tty));
+					return send_prio_char(tty, START_CHAR(tty));
 				break;
 			default:
 				return -EINVAL;
@@ -592,11 +597,11 @@ int n_tty_ioctl(struct tty_struct * tty,
 		case TIOCSSOFTCAR:
 			if (get_user(arg, (unsigned int __user *) arg))
 				return -EFAULT;
-			down(&tty->termios_sem);
+			mutex_lock(&tty->termios_mutex);
 			tty->termios->c_cflag =
 				((tty->termios->c_cflag & ~CLOCAL) |
 				 (arg ? CLOCAL : 0));
-			up(&tty->termios_sem);
+			mutex_unlock(&tty->termios_mutex);
 			return 0;
 		default:
 			return -ENOIOCTLCMD;
Index: linux-2.6.18.noarch/arch/sparc64/solaris/misc.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/sparc64/solaris/misc.c
+++ linux-2.6.18.noarch/arch/sparc64/solaris/misc.c
@@ -11,6 +11,7 @@
 #include <linux/limits.h>
 #include <linux/mm.h>
 #include <linux/smp.h>
+#include <linux/tty.h>
 #include <linux/mman.h>
 #include <linux/file.h>
 #include <linux/timex.h>
@@ -422,7 +423,9 @@ asmlinkage int solaris_procids(int cmd, 
 			   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);
 			return process_group(current);
 		}
 	case 2: /* getsid */
Index: linux-2.6.18.noarch/kernel/acct.c
===================================================================
--- linux-2.6.18.noarch.orig/kernel/acct.c
+++ linux-2.6.18.noarch/kernel/acct.c
@@ -483,10 +483,14 @@ static void do_acct_process(struct file 
 	ac.ac_ppid = current->parent->tgid;
 #endif
 
-	read_lock(&tasklist_lock);	/* pin current->signal */
+	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);
+	mutex_unlock(&tty_mutex);
 
 	spin_lock_irq(&current->sighand->siglock);
 	ac.ac_utime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_utime)));
Index: linux-2.6.18.noarch/kernel/auditsc.c
===================================================================
--- linux-2.6.18.noarch.orig/kernel/auditsc.c
+++ linux-2.6.18.noarch/kernel/auditsc.c
@@ -817,6 +817,8 @@ static void audit_log_exit(struct audit_
 		audit_log_format(ab, " success=%s exit=%ld", 
 				 (context->return_valid==AUDITSC_SUCCESS)?"yes":"no",
 				 context->return_code);
+
+	mutex_lock(&tty_mutex);
 	if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
 		tty = tsk->signal->tty->name;
 	else
@@ -838,6 +840,9 @@ static void audit_log_exit(struct audit_
 		  context->gid,
 		  context->euid, context->suid, context->fsuid,
 		  context->egid, context->sgid, context->fsgid, tty);
+
+	mutex_unlock(&tty_mutex);
+
 	audit_log_task_info(ab, tsk);
 	if (context->filterkey) {
 		audit_log_format(ab, " key=");

Date: Sun, 15 Oct 2006 13:53:03 -0400
From: Prarit Bhargava <prarit@redhat.com>
Subject: [RHEL5 PATCH 0/2 ]: BZ 210249 Additional tty locking fixups

Additional tty locking changes, and a revalidation of current->signal->tty.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>

--- linux-2.6.18.x86_64-1/drivers/char/tty_io.c	2006-10-15 11:32:57.000000000 -0400
+++ linux-2.6.18.x86_64-2/drivers/char/tty_io.c	2006-10-15 11:33:26.000000000 -0400
@@ -1361,8 +1361,10 @@ static void do_tty_hangup(void *data)
 	read_lock(&tasklist_lock);
 	if (tty->session > 0) {
 		do_each_task_pid(tty->session, PIDTYPE_SID, p) {
+			task_lock(p);
 			if (p->signal->tty == tty)
 				p->signal->tty = NULL;
+			task_unlock(p);
 			if (!p->signal->leader)
 				continue;
 			group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
@@ -1514,14 +1516,27 @@ void disassociate_ctty(int on_exit)
 
 	/* Must lock changes to tty_old_pgrp */
 	mutex_lock(&tty_mutex);
+	task_lock(current);
 	current->signal->tty_old_pgrp = 0;
-	tty->session = 0;
-	tty->pgrp = -1;
+
+	/* It is possible that do_tty_hangup has free'd this tty */
+	if (current->signal->tty) {
+		current->signal->tty->session = 0;
+		current->signal->tty->pgrp = -1;
+	} else {
+#ifdef TTY_DEBUG_HANGUP
+		printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
+		       " = NULL", tty);
+#endif
+	}
+	task_unlock(current);
 
 	/* Now clear signal->tty under the lock */
 	read_lock(&tasklist_lock);
 	do_each_task_pid(current->signal->session, PIDTYPE_SID, p) {
+		task_lock(p);
 		p->signal->tty = NULL;
+		task_unlock(p);
 	} while_each_task_pid(current->signal->session, PIDTYPE_SID, p);
 	read_unlock(&tasklist_lock);
 	mutex_unlock(&tty_mutex);