Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp
Hi Peter,
On Sun, Jun 28, 2015 at 3:27 PM, Peter Hurley wrote:
> The label name changing is not really necessary and would reduce diff count.
I've removed the label changes in the next series. Thanks for the feedback.
> It would be nice to get the printk() out from the locks as well (in a
> follow-on
> patch?)
I don't follow what you're referring to. Is it these lines?
if (!tty->pgrp) {
printk(KERN_WARNING "tty_check_change: tty->pgrp == NULL!\n");
--
Patrick Donnelly
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Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp
Hi Patrick,
On 06/27/2015 08:51 PM, Patrick Donnelly wrote:
> 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
> ---
> drivers/tty/tty_io.c | 24 +++-
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 57fc6ee..fbb55db 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -388,33 +388,39 @@ 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;
>
> - spin_lock_irqsave(&tty->ctrl_lock, flags);
> + 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;
> + goto out_irqunlock;
The label name changing is not really necessary and would reduce diff count.
It would be nice to get the printk() out from the locks as well (in a follow-on
patch?)
Regards,
Peter Hurley
> }
> - if (task_pgrp(current) == tty->pgrp)
> - goto out_unlock;
> + if (pgrp == tty->pgrp)
> + goto out_irqunlock;
> 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:
> +out_irqunlock:
> spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> +out_rcuunlock:
> + rcu_read_unlock();
> return ret;
> }
>
>
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Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp
On 06/28/2015 01:20 PM, Patrick Donnelly wrote: > On Sun, Jun 28, 2015 at 11:23 AM, Peter Hurley > wrote: >> On 06/27/2015 08:51 PM, Patrick Donnelly wrote: >>> 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. >> >> kill_pgrp() obtains tasklist_lock, so I don't see an unsafe deref. > > I see a race between looking up the pgrp via task_pgrp and passing it > to kill_pgrp. The pgrp struct pid may be freed via setpgid/setsid, as > mentioned in the comment for task_pgrp: > > * Without tasklist or rcu lock it is not safe to dereference > * the result of task_pgrp/task_session even if task == current, > * we can race with another thread doing sys_setsid/sys_setpgid. > > Getting the lock after the lookup is getting the lock too late. I > could be wrong though as I'm no expert on locking in Linux. I suppose it can't hurt; please add similar logic to job_control() in drivers/tty/n_tty.c which handles the corresponding SIGTTIN signal conditions. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp
On Sun, Jun 28, 2015 at 11:23 AM, Peter Hurley wrote: > On 06/27/2015 08:51 PM, Patrick Donnelly wrote: >> 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. > > kill_pgrp() obtains tasklist_lock, so I don't see an unsafe deref. I see a race between looking up the pgrp via task_pgrp and passing it to kill_pgrp. The pgrp struct pid may be freed via setpgid/setsid, as mentioned in the comment for task_pgrp: * Without tasklist or rcu lock it is not safe to dereference * the result of task_pgrp/task_session even if task == current, * we can race with another thread doing sys_setsid/sys_setpgid. Getting the lock after the lookup is getting the lock too late. I could be wrong though as I'm no expert on locking in Linux. -- Patrick Donnelly -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp
On 06/27/2015 08:51 PM, Patrick Donnelly wrote:
> 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.
kill_pgrp() obtains tasklist_lock, so I don't see an unsafe deref.
> Signed-off-by: Patrick Donnelly
> ---
> drivers/tty/tty_io.c | 24 +++-
> 1 file changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 57fc6ee..fbb55db 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -388,33 +388,39 @@ 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;
>
> - spin_lock_irqsave(&tty->ctrl_lock, flags);
> + 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;
> + goto out_irqunlock;
> }
> - if (task_pgrp(current) == tty->pgrp)
> - goto out_unlock;
> + if (pgrp == tty->pgrp)
> + goto out_irqunlock;
> 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:
> +out_irqunlock:
> spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> +out_rcuunlock:
> + rcu_read_unlock();
> return ret;
> }
>
>
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