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Subject[PATCH v4] tty: add missing rcu_read_lock for task_pgrp
Date
task_pgrp requires an rcu or tasklist lock to be obtained if the returned pid
is to be dereferenced, which kill_pgrp does. Obtain an RCU lock for the
duration of use.

Signed-off-by: Patrick Donnelly <batrick@batbytes.com>
---
drivers/tty/n_tty.c | 15 ++++++++++++---
drivers/tty/tty_io.c | 17 ++++++++++++-----
2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index c9c27f6..de67b2c 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2137,6 +2137,8 @@ extern ssize_t redirected_tty_write(struct file *, const char __user *,

static int job_control(struct tty_struct *tty, struct file *file)
{
+ struct pid *pgrp;
+
/* Job control check -- must be done at start and after
every sleep (POSIX.1 7.1.1.4). */
/* NOTE: not yet done after every sleep pending a thorough
@@ -2146,18 +2148,25 @@ static int job_control(struct tty_struct *tty, struct file *file)
current->signal->tty != tty)
return 0;

+ rcu_read_lock();
+ pgrp = task_pgrp(current);
+
spin_lock_irq(&tty->ctrl_lock);
if (!tty->pgrp)
printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
- else if (task_pgrp(current) != tty->pgrp) {
+ else if (pgrp != tty->pgrp) {
spin_unlock_irq(&tty->ctrl_lock);
- if (is_ignored(SIGTTIN) || is_current_pgrp_orphaned())
+ if (is_ignored(SIGTTIN) || is_current_pgrp_orphaned()) {
+ rcu_read_unlock();
return -EIO;
- kill_pgrp(task_pgrp(current), SIGTTIN, 1);
+ }
+ kill_pgrp(pgrp, SIGTTIN, 1);
+ rcu_read_unlock();
set_thread_flag(TIF_SIGPENDING);
return -ERESTARTSYS;
}
spin_unlock_irq(&tty->ctrl_lock);
+ rcu_read_unlock();
return 0;
}

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 57fc6ee..6bdfb98 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -388,33 +388,40 @@ EXPORT_SYMBOL_GPL(tty_find_polling_driver);
int tty_check_change(struct tty_struct *tty)
{
unsigned long flags;
+ struct pid *pgrp;
int ret = 0;

if (current->signal->tty != tty)
return 0;

+ rcu_read_lock();
+ pgrp = task_pgrp(current);
+
spin_lock_irqsave(&tty->ctrl_lock, flags);

if (!tty->pgrp) {
printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
goto out_unlock;
}
- if (task_pgrp(current) == tty->pgrp)
+ if (pgrp == tty->pgrp)
goto out_unlock;
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+
if (is_ignored(SIGTTOU))
- goto out;
+ goto out_rcuunlock;
if (is_current_pgrp_orphaned()) {
ret = -EIO;
- goto out;
+ goto out_rcuunlock;
}
- kill_pgrp(task_pgrp(current), SIGTTOU, 1);
+ kill_pgrp(pgrp, SIGTTOU, 1);
+ rcu_read_unlock();
set_thread_flag(TIF_SIGPENDING);
ret = -ERESTARTSYS;
-out:
return ret;
out_unlock:
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+out_rcuunlock:
+ rcu_read_unlock();
return ret;
}

--
Patrick Donnelly


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