From 47f86834bbd4193139d61d659bebf9ab9d691e37 Mon Sep 17 00:00:00 2001 From: Alan Cox Date: Wed, 30 Apr 2008 00:53:30 -0700 Subject: [PATCH] redo locking of tty->pgrp Historically tty->pgrp and friends were pid_t and the code "knew" they were safe. The change to pid structs opened up a few races and the removal of the BKL in places made them quite hittable. We put tty->pgrp under the ctrl_lock for the tty. Signed-off-by: Alan Cox Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/char/tty_io.c | 78 +++++++++++++++++++++++++++++++++---------- drivers/char/vt.c | 6 ++++ include/linux/tty.h | 10 +++--- 3 files changed, 72 insertions(+), 22 deletions(-) diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index 0b0354bc28d6..c8aa318eaa18 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -1204,26 +1204,37 @@ EXPORT_SYMBOL_GPL(tty_find_polling_driver); * not in the foreground, send a SIGTTOU. If the signal is blocked or * ignored, go ahead and perform the operation. (POSIX 7.2) * - * Locking: none - FIXME: review this + * Locking: ctrl_lock - FIXME: review this */ int tty_check_change(struct tty_struct *tty) { + unsigned long flags; + int ret = 0; + if (current->signal->tty != tty) return 0; + + spin_lock_irqsave(&tty->ctrl_lock, flags); + if (!tty->pgrp) { printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n"); - return 0; + goto out; } if (task_pgrp(current) == tty->pgrp) - return 0; + goto out; if (is_ignored(SIGTTOU)) - return 0; - if (is_current_pgrp_orphaned()) - return -EIO; + goto out; + if (is_current_pgrp_orphaned()) { + ret = -EIO; + goto out; + } kill_pgrp(task_pgrp(current), SIGTTOU, 1); set_thread_flag(TIF_SIGPENDING); - return -ERESTARTSYS; + ret = -ERESTARTSYS; +out: + spin_unlock_irqrestore(&tty->ctrl_lock, flags); + return ret; } EXPORT_SYMBOL(tty_check_change); @@ -1403,6 +1414,7 @@ static void do_tty_hangup(struct work_struct *work) struct task_struct *p; struct tty_ldisc *ld; int closecount = 0, n; + unsigned long flags; if (!tty) return; @@ -1479,19 +1491,24 @@ static void do_tty_hangup(struct work_struct *work) __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p); __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p); put_pid(p->signal->tty_old_pgrp); /* A noop */ + spin_lock_irqsave(&tty->ctrl_lock, flags); if (tty->pgrp) p->signal->tty_old_pgrp = get_pid(tty->pgrp); + spin_unlock_irqrestore(&tty->ctrl_lock, flags); spin_unlock_irq(&p->sighand->siglock); } while_each_pid_task(tty->session, PIDTYPE_SID, p); } read_unlock(&tasklist_lock); + spin_lock_irqsave(&tty->ctrl_lock, flags); tty->flags = 0; put_pid(tty->session); put_pid(tty->pgrp); tty->session = NULL; tty->pgrp = NULL; tty->ctrl_status = 0; + spin_unlock_irqrestore(&tty->ctrl_lock, flags); + /* * If one of the devices matches a console pointer, we * cannot just call hangup() because that will cause @@ -1666,10 +1683,13 @@ void disassociate_ctty(int on_exit) /* It is possible that do_tty_hangup has free'd this tty */ tty = get_current_tty(); if (tty) { + unsigned long flags; + spin_lock_irqsave(&tty->ctrl_lock, flags); put_pid(tty->session); put_pid(tty->pgrp); tty->session = NULL; tty->pgrp = NULL; + spin_unlock_irqrestore(&tty->ctrl_lock, flags); } else { #ifdef TTY_DEBUG_HANGUP printk(KERN_DEBUG "error attempted to write to tty [0x%p]" @@ -1785,10 +1805,8 @@ EXPORT_SYMBOL(start_tty); * for hung up devices before calling the line discipline method. * * Locking: - * Locks the line discipline internally while needed - * For historical reasons the line discipline read method is - * invoked under the BKL. This will go away in time so do not rely on it - * in new code. Multiple read calls may be outstanding in parallel. + * Locks the line discipline internally while needed. Multiple + * read calls may be outstanding in parallel. */ static ssize_t tty_read(struct file *file, char __user *buf, size_t count, @@ -2888,6 +2906,7 @@ static unsigned int tty_poll(struct file *filp, poll_table *wait) static int tty_fasync(int fd, struct file *filp, int on) { struct tty_struct *tty; + unsigned long flags; int retval; tty = (struct tty_struct *)filp->private_data; @@ -2903,6 +2922,7 @@ static int tty_fasync(int fd, struct file *filp, int on) struct pid *pid; if (!waitqueue_active(&tty->read_wait)) tty->minimum_to_wake = 1; + spin_lock_irqsave(&tty->ctrl_lock, flags); if (tty->pgrp) { pid = tty->pgrp; type = PIDTYPE_PGID; @@ -2910,6 +2930,7 @@ static int tty_fasync(int fd, struct file *filp, int on) pid = task_pid(current); type = PIDTYPE_PID; } + spin_unlock_irqrestore(&tty->ctrl_lock, flags); retval = __f_setown(filp, pid, type, 0); if (retval) return retval; @@ -2995,6 +3016,8 @@ static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty, struct winsize __user *arg) { struct winsize tmp_ws; + struct pid *pgrp, *rpgrp; + unsigned long flags; if (copy_from_user(&tmp_ws, arg, sizeof(*arg))) return -EFAULT; @@ -3012,10 +3035,21 @@ static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty, } } #endif - if (tty->pgrp) - kill_pgrp(tty->pgrp, SIGWINCH, 1); - if ((real_tty->pgrp != tty->pgrp) && real_tty->pgrp) - kill_pgrp(real_tty->pgrp, SIGWINCH, 1); + /* Get the PID values and reference them so we can + avoid holding the tty ctrl lock while sending signals */ + spin_lock_irqsave(&tty->ctrl_lock, flags); + pgrp = get_pid(tty->pgrp); + rpgrp = get_pid(real_tty->pgrp); + spin_unlock_irqrestore(&tty->ctrl_lock, flags); + + if (pgrp) + kill_pgrp(pgrp, SIGWINCH, 1); + if (rpgrp != pgrp && rpgrp) + kill_pgrp(rpgrp, SIGWINCH, 1); + + put_pid(pgrp); + put_pid(rpgrp); + tty->winsize = tmp_ws; real_tty->winsize = tmp_ws; done: @@ -3171,7 +3205,7 @@ static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t * Set the process group of the tty to the session passed. Only * permitted where the tty session is our session. * - * Locking: RCU + * Locking: RCU, ctrl lock */ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p) @@ -3179,6 +3213,7 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t struct pid *pgrp; pid_t pgrp_nr; int retval = tty_check_change(real_tty); + unsigned long flags; if (retval == -EIO) return -ENOTTY; @@ -3201,8 +3236,10 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t if (session_of_pgrp(pgrp) != task_session(current)) goto out_unlock; retval = 0; + spin_lock_irqsave(&tty->ctrl_lock, flags); put_pid(real_tty->pgrp); real_tty->pgrp = get_pid(pgrp); + spin_unlock_irqrestore(&tty->ctrl_lock, flags); out_unlock: rcu_read_unlock(); return retval; @@ -4077,14 +4114,19 @@ void proc_clear_tty(struct task_struct *p) } EXPORT_SYMBOL(proc_clear_tty); +/* Called under the sighand lock */ + static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty) { if (tty) { - /* We should not have a session or pgrp to here but.... */ + unsigned long flags; + /* We should not have a session or pgrp to put here but.... */ + spin_lock_irqsave(&tty->ctrl_lock, flags); put_pid(tty->session); put_pid(tty->pgrp); - tty->session = get_pid(task_session(tsk)); tty->pgrp = get_pid(task_pgrp(tsk)); + spin_unlock_irqrestore(&tty->ctrl_lock, flags); + tty->session = get_pid(task_session(tsk)); } put_pid(tsk->signal->tty_old_pgrp); tsk->signal->tty = tty; diff --git a/drivers/char/vt.c b/drivers/char/vt.c index e64f0bf3624e..c71d1d0f13b9 100644 --- a/drivers/char/vt.c +++ b/drivers/char/vt.c @@ -909,15 +909,21 @@ int vc_resize(struct vc_data *vc, unsigned int cols, unsigned int lines) if (vc->vc_tty) { struct winsize ws, *cws = &vc->vc_tty->winsize; + unsigned long flags; memset(&ws, 0, sizeof(ws)); ws.ws_row = vc->vc_rows; ws.ws_col = vc->vc_cols; ws.ws_ypixel = vc->vc_scan_lines; + + mutex_lock(&vc->vc_tty->termios_mutex); + spin_lock_irqsave(&vc->vc_tty->ctrl_lock, flags); if ((ws.ws_row != cws->ws_row || ws.ws_col != cws->ws_col) && vc->vc_tty->pgrp) kill_pgrp(vc->vc_tty->pgrp, SIGWINCH, 1); + spin_unlock_irqrestore(&vc->vc_tty->ctrl_lock, flags); *cws = ws; + mutex_unlock(&vc->vc_tty->termios_mutex); } if (CON_IS_VISIBLE(vc)) diff --git a/include/linux/tty.h b/include/linux/tty.h index 4d3702bade03..381085e45cca 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -184,21 +184,22 @@ struct tty_struct { struct tty_ldisc ldisc; struct mutex termios_mutex; spinlock_t ctrl_lock; + /* Termios values are protected by the termios mutex */ struct ktermios *termios, *termios_locked; char name[64]; - struct pid *pgrp; + struct pid *pgrp; /* Protected by ctrl lock */ struct pid *session; unsigned long flags; int count; - struct winsize winsize; + struct winsize winsize; /* termios mutex */ unsigned char stopped:1, hw_stopped:1, flow_stopped:1, packet:1; unsigned char low_latency:1, warned:1; - unsigned char ctrl_status; + unsigned char ctrl_status; /* ctrl_lock */ unsigned int receive_room; /* Bytes free for queue */ struct tty_struct *link; struct fasync_struct *fasync; - struct tty_bufhead buf; + struct tty_bufhead buf; /* Locked internally */ int alt_speed; /* For magic substitution of 38400 bps */ wait_queue_head_t write_wait; wait_queue_head_t read_wait; @@ -212,6 +213,7 @@ struct tty_struct { /* * The following is data for the N_TTY line discipline. For * historical reasons, this is included in the tty structure. + * Mostly locked by the BKL. */ unsigned int column; unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1; -- 2.20.1