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    Subject[PATCH 36/76] tty: Make get_current_tty use a kref
    Date
    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>
    ---

    drivers/char/tty_io.c | 10 ++++++----
    drivers/s390/char/fs3270.c | 3 ++-
    fs/dquot.c | 6 +++---
    security/selinux/hooks.c | 3 ++-
    4 files changed, 13 insertions(+), 9 deletions(-)

    diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
    index 9a76db3..4c0e4ed 100644
    --- 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
    --- 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
    --- 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 03fc6a8..c856db8 100644
    --- a/security/selinux/hooks.c
    +++ b/security/selinux/hooks.c
    @@ -2122,6 +2122,7 @@ 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);
    @@ -2138,8 +2139,8 @@ 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();


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