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Commit 81af8d67 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Linus Torvalds
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[PATCH] vt: rework the console spawning variables 



This is such a rare path it took me a while to figure out how to test
this after soring out the locking.

This patch does several things.
- The variables used are moved into a structure and declared in vt_kern.h
- A spinlock is added so we don't have SMP races updating the values.
- Instead of raw pid_t value a struct_pid is used to guard against
  pid wrap around issues, if the daemon to spawn a new console dies.

Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5feb8f5f

drivers/char/keyboard.c

+12 −4
Original line number Diff line number Diff line
@@ -108,7 +108,11 @@ const int NR_TYPES = ARRAY_SIZE(max_vals); 
struct kbd_struct kbd_table[MAX_NR_CONSOLES];

static struct kbd_struct *kbd = kbd_table;



int spawnpid, spawnsig;

struct vt_spawn_console vt_spawn_con = {

	.lock = SPIN_LOCK_UNLOCKED,

	.pid  = NULL,

	.sig  = 0,

};



/*

 * Variables exported for vt.c
@@ -578,9 +582,13 @@ static void fn_compose(struct vc_data *vc, struct pt_regs *regs) 


static void fn_spawn_con(struct vc_data *vc, struct pt_regs *regs)

{

	if (spawnpid)

		if (kill_proc(spawnpid, spawnsig, 1))

			spawnpid = 0;

	spin_lock(&vt_spawn_con.lock);

	if (vt_spawn_con.pid)

		if (kill_pid(vt_spawn_con.pid, vt_spawn_con.sig, 1)) {

			put_pid(vt_spawn_con.pid);

			vt_spawn_con.pid = NULL;

		}

	spin_unlock(&vt_spawn_con.lock);

}



static void fn_SAK(struct vc_data *vc, struct pt_regs *regs)

drivers/char/vt_ioctl.c

+6 −3
Original line number Diff line number Diff line
@@ -645,13 +645,16 @@ int vt_ioctl(struct tty_struct *tty, struct file * file, 
	 */

	case KDSIGACCEPT:

	{

		extern int spawnpid, spawnsig;

		if (!perm || !capable(CAP_KILL))

		  return -EPERM;

		if (!valid_signal(arg) || arg < 1 || arg == SIGKILL)

		  return -EINVAL;

		spawnpid = current->pid;

		spawnsig = arg;



		spin_lock_irq(&vt_spawn_con.lock);

		put_pid(vt_spawn_con.pid);

		vt_spawn_con.pid = get_pid(task_pid(current));

		vt_spawn_con.sig = arg;

		spin_unlock_irq(&vt_spawn_con.lock);

		return 0;

	}

include/linux/vt_kern.h

+7 −0
Original line number Diff line number Diff line
@@ -84,4 +84,11 @@ void reset_vc(struct vc_data *vc); 
extern char con_buf[CON_BUF_SIZE];

extern struct semaphore con_buf_sem;



struct vt_spawn_console {

	spinlock_t lock;

	struct pid *pid;

	int sig;

};

extern struct vt_spawn_console vt_spawn_con;



#endif /* _VT_KERN_H */