[PATCH 42/80] tty: Make get_current_tty use a kref

Alan Cox
2008-10-13T09:48:43Z

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 4a7374c..089d61a 100644
--- 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();