tty: Make get_current_tty use a kref

We now return a kref covered tty reference. That ensures the tty structure
doesn't go away when you have a return from get_current_tty. This is not
enough to protect you from most of the resources being freed behind your
back - yet.

[Updated to include fixes for SELinux problems found by Andrew Morton and
 an s390 leak found while debugging the former]

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 9a76db3..4c0e4ed 100644 (file)
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -786,12 +786,12 @@ void disassociate_ctty(int on_exit)
        tty = get_current_tty();
        if (tty) {
                tty_pgrp = get_pid(tty->pgrp);
-               lock_kernel();
                mutex_unlock(&tty_mutex);
-               /* XXX: here we race, there is nothing protecting tty */
+               lock_kernel();
                if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
                        tty_vhangup(tty);
                unlock_kernel();
+               tty_kref_put(tty);
        } else if (on_exit) {
                struct pid *old_pgrp;
                spin_lock_irq(&current->sighand->siglock);
@@ -819,7 +819,6 @@ void disassociate_ctty(int on_exit)
        spin_unlock_irq(&current->sighand->siglock);
 
        mutex_lock(&tty_mutex);
-       /* It is possible that do_tty_hangup has free'd this tty */
        tty = get_current_tty();
        if (tty) {
                unsigned long flags;
@@ -829,6 +828,7 @@ void disassociate_ctty(int on_exit)
                tty->session = NULL;
                tty->pgrp = NULL;
                spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+               tty_kref_put(tty);
        } else {
 #ifdef TTY_DEBUG_HANGUP
                printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
@@ -1806,6 +1806,8 @@ retry_open:
                index = tty->index;
                filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
                /* noctty = 1; */
+               /* FIXME: Should we take a driver reference ? */
+               tty_kref_put(tty);
                goto got_driver;
        }
 #ifdef CONFIG_VT
@@ -3135,7 +3137,7 @@ struct tty_struct *get_current_tty(void)
 {
        struct tty_struct *tty;
        WARN_ON_ONCE(!mutex_is_locked(&tty_mutex));
-       tty = current->signal->tty;
+       tty = tty_kref_get(current->signal->tty);
        /*
         * session->tty can be changed/cleared from under us, make sure we
         * issue the load. The obtained pointer, when not NULL, is valid as

diff --git a/drivers/s390/char/fs3270.c b/drivers/s390/char/fs3270.c
index d18e6d2..3ef5425 100644 (file)
--- a/drivers/s390/char/fs3270.c
+++ b/drivers/s390/char/fs3270.c
@@ -430,11 +430,12 @@ fs3270_open(struct inode *inode, struct file *filp)
                mutex_lock(&tty_mutex);
                tty = get_current_tty();
                if (!tty || tty->driver->major != IBM_TTY3270_MAJOR) {
-                       mutex_unlock(&tty_mutex);
+                       tty_kref_put(tty);
                        rc = -ENODEV;
                        goto out;
                }
                minor = tty->index + RAW3270_FIRSTMINOR;
+               tty_kref_put(tty);
                mutex_unlock(&tty_mutex);
        }
        /* Check if some other program is already using fullscreen mode. */

diff --git a/fs/dquot.c b/fs/dquot.c
index 8ec4d6c..7417a6c 100644 (file)
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -897,8 +897,9 @@ static void print_warning(struct dquot *dquot, const int warntype)
 
        mutex_lock(&tty_mutex);
        tty = get_current_tty();
+       mutex_unlock(&tty_mutex);
        if (!tty)
-               goto out_lock;
+               return;
        tty_write_message(tty, dquot->dq_sb->s_id);
        if (warntype == QUOTA_NL_ISOFTWARN || warntype == QUOTA_NL_BSOFTWARN)
                tty_write_message(tty, ": warning, ");
@@ -926,8 +927,7 @@ static void print_warning(struct dquot *dquot, const int warntype)
                        break;
        }
        tty_write_message(tty, msg);
-out_lock:
-       mutex_unlock(&tty_mutex);
+       tty_kref_put(tty);
 }
 #endif
 

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 4a7374c..089d61a 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2123,6 +2123,7 @@ static inline void flush_unauthorized_files(struct files_struct *files)
 
        mutex_lock(&tty_mutex);
        tty = get_current_tty();
+       mutex_unlock(&tty_mutex);
        if (tty) {
                file_list_lock();
                file = list_entry(tty->tty_files.next, typeof(*file), f_u.fu_list);
@@ -2139,8 +2140,8 @@ static inline void flush_unauthorized_files(struct files_struct *files)
                        }
                }
                file_list_unlock();
+               tty_kref_put(tty);
        }
-       mutex_unlock(&tty_mutex);
        /* Reset controlling tty. */
        if (drop_tty)
                no_tty();