Re: [RFC][PATCH] ->signal->tty locking

From: Peter Zijlstra
Date: Tue Oct 17 2006 - 09:00:16 EST

On Tue, 2006-10-17 at 16:33 +0400, Oleg Nesterov wrote:
> On 10/17, Peter Zijlstra wrote:

> > Hmm, either sys_unshare() is broken in that it doesn't take the
> > tasklist_lock or a lot of other code is broken.
>
> Yes, it is broken, please look at

Ah good :-)

How about something like this; I'm still shaky on the lifetime rules of
tty objects, I'm about to add a refcount and spinlock/mutex to
tty_struct, this is madness....

---
arch/sparc64/solaris/misc.c | 4 -
arch/um/kernel/exec.c | 7 +-
drivers/char/tty_io.c | 126 ++++++++++++++++++++++++--------------------
drivers/s390/char/fs3270.c | 10 ++-
fs/dquot.c | 14 ++--
fs/open.c | 1
include/linux/tty.h | 28 +++++++++
kernel/acct.c | 9 +--
kernel/auditsc.c | 2
kernel/exit.c | 4 -
kernel/sys.c | 6 +-
security/selinux/hooks.c | 15 +++--
12 files changed, 141 insertions(+), 85 deletions(-)

Index: linux-2.6.18.noarch/drivers/char/tty_io.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/char/tty_io.c
+++ linux-2.6.18.noarch/drivers/char/tty_io.c
@@ -126,7 +126,7 @@ EXPORT_SYMBOL(tty_std_termios);

LIST_HEAD(tty_drivers); /* linked list of tty drivers */

-/* Semaphore to protect creating and releasing a tty. This is shared with
+/* Mutex to protect creating and releasing a tty. This is shared with
vt.c for deeply disgusting hack reasons */
DEFINE_MUTEX(tty_mutex);
EXPORT_SYMBOL(tty_mutex);
@@ -616,7 +616,7 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_strin
* they are not on hot paths so a little discipline won't do
* any harm.
*
- * Locking: takes termios_sem
+ * Locking: takes termios_mutex
*/

static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
@@ -917,7 +917,7 @@ static void tty_ldisc_enable(struct tty_
* context.
*
* Locking: takes tty_ldisc_lock.
- * called functions take termios_sem
+ * called functions take termios_mutex
*/

static int tty_set_ldisc(struct tty_struct *tty, int ldisc)
@@ -1269,12 +1269,12 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush);
*
* Locking:
* BKL
- * redirect lock for undoing redirection
- * file list lock for manipulating list of ttys
- * tty_ldisc_lock from called functions
- * termios_sem resetting termios data
- * tasklist_lock to walk task list for hangup event
- *
+ * redirect lock for undoing redirection
+ * file list lock for manipulating list of ttys
+ * tty_ldisc_lock from called functions
+ * termios_mutex resetting termios data
+ * tasklist_lock to walk task list for hangup event
+ * ->siglock to protect ->signal/->sighand
*/
static void do_tty_hangup(void *data)
{
@@ -1355,14 +1355,18 @@ static void do_tty_hangup(void *data)
read_lock(&tasklist_lock);
if (tty->session > 0) {
do_each_task_pid(tty->session, PIDTYPE_SID, p) {
+ spin_lock_irq(&p->sighand->siglock);
if (p->signal->tty == tty)
p->signal->tty = NULL;
- if (!p->signal->leader)
+ if (!p->signal->leader) {
+ spin_unlock_irq(&p->sighand->siglock);
continue;
- group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
- group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
+ }
+ __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
+ __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
if (tty->pgrp > 0)
p->signal->tty_old_pgrp = tty->pgrp;
+ spin_unlock_irq(&p->sighand->siglock);
} while_each_task_pid(tty->session, PIDTYPE_SID, p);
}
read_unlock(&tasklist_lock);
@@ -1470,10 +1474,12 @@ EXPORT_SYMBOL(tty_hung_up_p);
* The argument on_exit is set to 1 if called when a process is
* exiting; it is 0 if called by the ioctl TIOCNOTTY.
*
- * Locking: tty_mutex is taken to protect current->signal->tty
+ * Locking:
* BKL is taken for hysterical raisins
- * Tasklist lock is taken (under tty_mutex) to walk process
- * lists for the session.
+ * tty_mutex is taken to protect tty
+ * ->siglock is taken to protect ->signal/->sighand
+ * tasklist_lock is taken to walk process list for sessions
+ * ->siglock is taken to protect ->signal/->sighand
*/

void disassociate_ctty(int on_exit)
@@ -1481,20 +1487,23 @@ void disassociate_ctty(int on_exit)
struct tty_struct *tty;
struct task_struct *p;
int tty_pgrp = -1;
+ int session;

lock_kernel();

mutex_lock(&tty_mutex);
- tty = current->signal->tty;
+ tty = current_get_tty();
if (tty) {
tty_pgrp = tty->pgrp;
mutex_unlock(&tty_mutex);
+ /* XXX: here we race, there is nothing protecting tty */
if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
tty_vhangup(tty);
} else {
- if (current->signal->tty_old_pgrp) {
- kill_pg(current->signal->tty_old_pgrp, SIGHUP, on_exit);
- kill_pg(current->signal->tty_old_pgrp, SIGCONT, on_exit);
+ pid_t old_pgrp = current->signal->tty_old_pgrp;
+ if (old_pgrp) {
+ kill_pg(old_pgrp, SIGHUP, on_exit);
+ kill_pg(old_pgrp, SIGCONT, on_exit);
}
mutex_unlock(&tty_mutex);
unlock_kernel();
@@ -1506,19 +1515,29 @@ void disassociate_ctty(int on_exit)
kill_pg(tty_pgrp, SIGCONT, on_exit);
}

- /* Must lock changes to tty_old_pgrp */
- mutex_lock(&tty_mutex);
+ spin_lock_irq(&current->sighand->siglock);
current->signal->tty_old_pgrp = 0;
- tty->session = 0;
- tty->pgrp = -1;
+ session = current->signal->session;
+ spin_unlock_irq(&current->sighand->siglock);
+
+ mutex_lock(&tty_mutex);
+ /* It is possible that do_tty_hangup has free'd this tty */
+ tty = current_get_tty();
+ if (tty) {
+ tty->session = 0;
+ tty->pgrp = 0;
+ } else {
+#ifdef TTY_DEBUG_HANGUP
+ printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
+ " = NULL", tty);
+#endif
+ }
+ mutex_unlock(&tty_mutex);

/* Now clear signal->tty under the lock */
read_lock(&tasklist_lock);
- do_each_task_pid(current->signal->session, PIDTYPE_SID, p) {
- p->signal->tty = NULL;
- } while_each_task_pid(current->signal->session, PIDTYPE_SID, p);
+ session_clear_tty(session);
read_unlock(&tasklist_lock);
- mutex_unlock(&tty_mutex);
unlock_kernel();
}

@@ -2340,13 +2359,9 @@ static void release_dev(struct file * fi
struct task_struct *p;

read_lock(&tasklist_lock);
- do_each_task_pid(tty->session, PIDTYPE_SID, p) {
- p->signal->tty = NULL;
- } while_each_task_pid(tty->session, PIDTYPE_SID, p);
+ session_clear_tty(tty->session);
if (o_tty)
- do_each_task_pid(o_tty->session, PIDTYPE_SID, p) {
- p->signal->tty = NULL;
- } while_each_task_pid(o_tty->session, PIDTYPE_SID, p);
+ session_clear_tty(o_tty->session);
read_unlock(&tasklist_lock);
}

@@ -2467,12 +2482,13 @@ retry_open:
mutex_lock(&tty_mutex);

if (device == MKDEV(TTYAUX_MAJOR,0)) {
- if (!current->signal->tty) {
+ tty = current_get_tty();
+ if (!tty) {
mutex_unlock(&tty_mutex);
return -ENXIO;
}
- driver = current->signal->tty->driver;
- index = current->signal->tty->index;
+ driver = tty->driver;
+ index = tty->index;
filp->f_flags |= O_NONBLOCK; /* Don't let /dev/tty block */
/* noctty = 1; */
goto got_driver;
@@ -2547,17 +2563,21 @@ got_driver:
filp->f_op = &tty_fops;
goto retry_open;
}
+
+ mutex_lock(&tty_mutex);
+ spin_lock_irq(&current->sighand->siglock);
if (!noctty &&
current->signal->leader &&
!current->signal->tty &&
tty->session == 0) {
- task_lock(current);
current->signal->tty = tty;
- task_unlock(current);
current->signal->tty_old_pgrp = 0;
tty->session = current->signal->session;
tty->pgrp = process_group(current);
}
+ /* don't we leak tty in the else case !? */
+ spin_unlock_irq(&current->sighand->siglock);
+ mutex_unlock(&tty_mutex);
return 0;
}

@@ -2899,6 +2919,7 @@ static int tiocsctty(struct tty_struct *
*/
if (!current->signal->leader || current->signal->tty)
return -EPERM;
+ mutex_lock(&tty_mutex);
if (tty->session > 0) {
/*
* This tty is already the controlling
@@ -2908,23 +2929,21 @@ static int tiocsctty(struct tty_struct *
/*
* Steal it away
*/
-
read_lock(&tasklist_lock);
- do_each_task_pid(tty->session, PIDTYPE_SID, p) {
- p->signal->tty = NULL;
- } while_each_task_pid(tty->session, PIDTYPE_SID, p);
+ session_clear_tty(tty->session);
read_unlock(&tasklist_lock);
- } else
+ } else {
+ mutex_unlock(&tty_mutex);
return -EPERM;
+ }
}
- mutex_lock(&tty_mutex);
- task_lock(current);
- current->signal->tty = tty;
- task_unlock(current);
- mutex_unlock(&tty_mutex);
- current->signal->tty_old_pgrp = 0;
+ spin_lock_irq(&current->sighand->siglock);
tty->session = current->signal->session;
tty->pgrp = process_group(current);
+ current->signal->tty = tty;
+ current->signal->tty_old_pgrp = 0;
+ spin_unlock_irq(&current->sighand->siglock);
+ mutex_unlock(&tty_mutex);
return 0;
}

@@ -2937,7 +2956,7 @@ static int tiocsctty(struct tty_struct *
* Obtain the process group of the tty. If there is no process group
* return an error.
*
- * Locking: none. Reference to ->signal->tty is safe.
+ * Locking: none. Reference to current->signal->tty is safe.
*/

static int tiocgpgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
@@ -2995,7 +3014,7 @@ static int tiocspgrp(struct tty_struct *
* Obtain the session id of the tty. If there is no session
* return an error.
*
- * Locking: none. Reference to ->signal->tty is safe.
+ * Locking: none. Reference to current->signal->tty is safe.
*/

static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
@@ -3214,14 +3233,11 @@ int tty_ioctl(struct inode * inode, stru
clear_bit(TTY_EXCLUSIVE, &tty->flags);
return 0;
case TIOCNOTTY:
- /* FIXME: taks lock or tty_mutex ? */
if (current->signal->tty != tty)
return -ENOTTY;
if (current->signal->leader)
disassociate_ctty(0);
- task_lock(current);
- current->signal->tty = NULL;
- task_unlock(current);
+ proc_set_tty(current, NULL);
return 0;
case TIOCSCTTY:
return tiocsctty(tty, arg);
Index: linux-2.6.18.noarch/kernel/auditsc.c
===================================================================
--- linux-2.6.18.noarch.orig/kernel/auditsc.c
+++ linux-2.6.18.noarch/kernel/auditsc.c
@@ -819,10 +819,12 @@ static void audit_log_exit(struct audit_
context->return_code);

mutex_lock(&tty_mutex);
+ read_lock(&tasklist_lock);
if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
tty = tsk->signal->tty->name;
else
tty = "(none)";
+ read_unlock(&tasklist_lock);
audit_log_format(ab,
" a0=%lx a1=%lx a2=%lx a3=%lx items=%d"
" ppid=%d pid=%d auid=%u uid=%u gid=%u"
Index: linux-2.6.18.noarch/kernel/exit.c
===================================================================
--- linux-2.6.18.noarch.orig/kernel/exit.c
+++ linux-2.6.18.noarch/kernel/exit.c
@@ -382,9 +382,7 @@ void daemonize(const char *name, ...)
exit_mm(current);

set_special_pids(1, 1);
- mutex_lock(&tty_mutex);
- current->signal->tty = NULL;
- mutex_unlock(&tty_mutex);
+ proc_set_tty(current, NULL);

/* Block and flush all signals */
sigfillset(&blocked);
Index: linux-2.6.18.noarch/kernel/sys.c
===================================================================
--- linux-2.6.18.noarch.orig/kernel/sys.c
+++ linux-2.6.18.noarch/kernel/sys.c
@@ -1379,7 +1379,6 @@ asmlinkage long sys_setsid(void)
pid_t session;
int err = -EPERM;

- mutex_lock(&tty_mutex);
write_lock_irq(&tasklist_lock);

/* Fail if I am already a session leader */
@@ -1399,12 +1398,15 @@ asmlinkage long sys_setsid(void)

group_leader->signal->leader = 1;
__set_special_pids(session, session);
+
+ spin_lock(&group_leader->sighand->siglock);
group_leader->signal->tty = NULL;
group_leader->signal->tty_old_pgrp = 0;
+ spin_unlock(&group_leader->sighand->siglock);
+
err = process_group(group_leader);
out:
write_unlock_irq(&tasklist_lock);
- mutex_unlock(&tty_mutex);
return err;
}

Index: linux-2.6.18.noarch/arch/sparc64/solaris/misc.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/sparc64/solaris/misc.c
+++ linux-2.6.18.noarch/arch/sparc64/solaris/misc.c
@@ -423,9 +423,7 @@ asmlinkage int solaris_procids(int cmd,
Solaris setpgrp and setsid? */
ret = sys_setpgid(0, 0);
if (ret) return ret;
- mutex_lock(&tty_mutex);
- current->signal->tty = NULL;
- mutex_unlock(&tty_mutex);
+ proc_set_tty(current, NULL);
return process_group(current);
}
case 2: /* getsid */
Index: linux-2.6.18.noarch/arch/um/kernel/exec.c
===================================================================
--- linux-2.6.18.noarch.orig/arch/um/kernel/exec.c
+++ linux-2.6.18.noarch/arch/um/kernel/exec.c
@@ -39,12 +39,13 @@ static long execve1(char *file, char __u
char __user *__user *env)
{
long error;
+ struct tty_struct *tty;

#ifdef CONFIG_TTY_LOG
mutex_lock(&tty_mutex);
- task_lock(current); /* FIXME: is this needed ? */
- log_exec(argv, current->signal->tty);
- task_unlock(current);
+ tty = current_get_tty();
+ if (tty)
+ log_exec(argv, tty);
mutex_unlock(&tty_mutex);
#endif
error = do_execve(file, argv, env, &current->thread.regs);
Index: linux-2.6.18.noarch/drivers/s390/char/fs3270.c
===================================================================
--- linux-2.6.18.noarch.orig/drivers/s390/char/fs3270.c
+++ linux-2.6.18.noarch/drivers/s390/char/fs3270.c
@@ -425,11 +425,15 @@ fs3270_open(struct inode *inode, struct
minor = iminor(filp->f_dentry->d_inode);
/* Check for minor 0 multiplexer. */
if (minor == 0) {
- if (!current->signal->tty)
+ struct tty_struct *tty;
+ mutex_lock(&tty_mutex);
+ tty = current_get_tty();
+ if (!tty)
return -ENODEV;
- if (current->signal->tty->driver->major != IBM_TTY3270_MAJOR)
+ if (tty->driver->major != IBM_TTY3270_MAJOR)
return -ENODEV;
- minor = current->signal->tty->index + RAW3270_FIRSTMINOR;
+ minor = tty->index + RAW3270_FIRSTMINOR;
+ mutex_unlock(&tty_mutex);
}
/* Check if some other program is already using fullscreen mode. */
fp = (struct fs3270 *) raw3270_find_view(&fs3270_fn, minor);
Index: linux-2.6.18.noarch/fs/dquot.c
===================================================================
--- linux-2.6.18.noarch.orig/fs/dquot.c
+++ linux-2.6.18.noarch/fs/dquot.c
@@ -828,6 +828,7 @@ static inline int need_print_warning(str
static void print_warning(struct dquot *dquot, const char warntype)
{
char *msg = NULL;
+ struct tty_struct *tty;
int flag = (warntype == BHARDWARN || warntype == BSOFTLONGWARN) ? DQ_BLKS_B :
((warntype == IHARDWARN || warntype == ISOFTLONGWARN) ? DQ_INODES_B : 0);

@@ -835,14 +836,15 @@ static void print_warning(struct dquot *
return;

mutex_lock(&tty_mutex);
- if (!current->signal->tty)
+ tty = current_get_tty();
+ if (!tty)
goto out_lock;
- tty_write_message(current->signal->tty, dquot->dq_sb->s_id);
+ tty_write_message(tty, dquot->dq_sb->s_id);
if (warntype == ISOFTWARN || warntype == BSOFTWARN)
- tty_write_message(current->signal->tty, ": warning, ");
+ tty_write_message(tty, ": warning, ");
else
- tty_write_message(current->signal->tty, ": write failed, ");
- tty_write_message(current->signal->tty, quotatypes[dquot->dq_type]);
+ tty_write_message(tty, ": write failed, ");
+ tty_write_message(tty, quotatypes[dquot->dq_type]);
switch (warntype) {
case IHARDWARN:
msg = " file limit reached.\r\n";
@@ -863,7 +865,7 @@ static void print_warning(struct dquot *
msg = " block quota exceeded.\r\n";
break;
}
- tty_write_message(current->signal->tty, msg);
+ tty_write_message(tty, msg);
out_lock:
mutex_unlock(&tty_mutex);
}
Index: linux-2.6.18.noarch/fs/open.c
===================================================================
--- linux-2.6.18.noarch.orig/fs/open.c
+++ linux-2.6.18.noarch/fs/open.c
@@ -1204,6 +1204,7 @@ EXPORT_SYMBOL(sys_close);
asmlinkage long sys_vhangup(void)
{
if (capable(CAP_SYS_TTY_CONFIG)) {
+ /* XXX: this needs locking */
tty_vhangup(current->signal->tty);
return 0;
}
Index: linux-2.6.18.noarch/include/linux/tty.h
===================================================================
--- linux-2.6.18.noarch.orig/include/linux/tty.h
+++ linux-2.6.18.noarch/include/linux/tty.h
@@ -338,5 +338,33 @@ static inline dev_t tty_devnum(struct tt
return MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
}

+static inline void proc_set_tty(struct task_struct *p, struct tty_struct *tty)
+{
+ spin_lock_irq(&p->sighand->siglock);
+ p->signal->tty = tty;
+ spin_unlock_irq(&p->sighand->siglock);
+}
+
+static inline void session_clear_tty(pid_t session)
+{
+ struct task_struct *p;
+ do_each_task_pid(session, PIDTYPE_SID, p) {
+ proc_set_tty(p, NULL);
+ } while_each_task_pid(session, PIDTYPE_SID, p);
+}
+
+static inline void current_get_tty(void)
+{
+ struct tty_struct *tty;
+ WARN_ON_ONCE(!mutex_locked(&tty_mutex));
+ tty = current->session->tty;
+ barrier();
+ /*
+ * ->tty could be changed/cleared from under us, but it can't be
+ * released while we are holding tty_mutex
+ */
+ return tty;
+}
+
#endif /* __KERNEL__ */
#endif
Index: linux-2.6.18.noarch/kernel/acct.c
===================================================================
--- linux-2.6.18.noarch.orig/kernel/acct.c
+++ linux-2.6.18.noarch/kernel/acct.c
@@ -427,6 +427,7 @@ static void do_acct_process(struct file
u64 elapsed;
u64 run_time;
struct timespec uptime;
+ struct tty_struct *tty;

/*
* First check to see if there is enough free_space to continue
@@ -484,12 +485,8 @@ static void do_acct_process(struct file
#endif

mutex_lock(&tty_mutex);
- /* FIXME: Whoever is responsible for current->signal locking needs
- to use the same locking all over the kernel and document it */
- read_lock(&tasklist_lock);
- ac.ac_tty = current->signal->tty ?
- old_encode_dev(tty_devnum(current->signal->tty)) : 0;
- read_unlock(&tasklist_lock);
+ tty = current_get_tty();
+ ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
mutex_unlock(&tty_mutex);

spin_lock_irq(&current->sighand->siglock);
Index: linux-2.6.18.noarch/security/selinux/hooks.c
===================================================================
--- linux-2.6.18.noarch.orig/security/selinux/hooks.c
+++ linux-2.6.18.noarch/security/selinux/hooks.c
@@ -1708,9 +1708,10 @@ static inline void flush_unauthorized_fi
struct tty_struct *tty;
struct fdtable *fdt;
long j = -1;
+ int drop_tty = 0;

mutex_lock(&tty_mutex);
- tty = current->signal->tty;
+ tty = current_get_tty();
if (tty) {
file_list_lock();
file = list_entry(tty->tty_files.next, typeof(*file), f_u.fu_list);
@@ -1723,12 +1724,18 @@ static inline void flush_unauthorized_fi
struct inode *inode = file->f_dentry->d_inode;
if (inode_has_perm(current, inode,
FILE__READ | FILE__WRITE, NULL)) {
- /* Reset controlling tty. */
- current->signal->tty = NULL;
- current->signal->tty_old_pgrp = 0;
+ drop_tty = 1;
}
}
file_list_unlock();
+
+ if (drop_tty) {
+ /* Reset controlling tty. */
+ spin_lock_irq(&current->sighand->siglock);
+ current->signal->tty = NULL;
+ current->signal->tty_old_pgrp = 0;
+ spin_unlock_irq(&current->sighand->siglock);
+ }
}
mutex_unlock(&tty_mutex);



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