[SRU,X/B/C] tty: Don't hold ldisc lock in tty_reopen() if ldisc present
diff mbox series

Message ID 20190130154323.11569-1-stefan.bader@canonical.com
State New
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  • [SRU,X/B/C] tty: Don't hold ldisc lock in tty_reopen() if ldisc present
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Commit Message

Stefan Bader Jan. 30, 2019, 3:43 p.m. UTC
From: Dmitry Safonov <dima@arista.com>

BugLink: https://bugs.launchpad.net/bugs/1813873

Try to get reference for ldisc during tty_reopen().
If ldisc present, we don't need to do tty_ldisc_reinit() and lock the
write side for line discipline semaphore.
Effectively, it optimizes fast-path for tty_reopen(), but more
importantly it won't interrupt ongoing IO on the tty as no ldisc change
is needed.
Fixes user-visible issue when tty_reopen() interrupted login process for
user with a long password, observed and reported by Lukas.

Fixes: c96cf923a98d ("tty: Don't block on IO when ldisc change is pending")
Fixes: 83d817f41070 ("tty: Hold tty_ldisc_lock() during tty_reopen()")
Cc: Jiri Slaby <jslaby@suse.com>
Reported-by: Lukas F. Hartmann <lukas@mntmn.com>
Tested-by: Lukas F. Hartmann <lukas@mntmn.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit d3736d82e8169768218ee0ef68718875918091a0)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---

The commits being fixed got requested via LP: #1791758 but
were missing this follow-up.  Compile-tested on Xenial.

-Stefan

 drivers/tty/tty_io.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

Comments

Colin Ian King Jan. 30, 2019, 4:01 p.m. UTC | #1
On 30/01/2019 15:43, Stefan Bader wrote:
> From: Dmitry Safonov <dima@arista.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1813873
> 
> Try to get reference for ldisc during tty_reopen().
> If ldisc present, we don't need to do tty_ldisc_reinit() and lock the
> write side for line discipline semaphore.
> Effectively, it optimizes fast-path for tty_reopen(), but more
> importantly it won't interrupt ongoing IO on the tty as no ldisc change
> is needed.
> Fixes user-visible issue when tty_reopen() interrupted login process for
> user with a long password, observed and reported by Lukas.
> 
> Fixes: c96cf923a98d ("tty: Don't block on IO when ldisc change is pending")
> Fixes: 83d817f41070 ("tty: Hold tty_ldisc_lock() during tty_reopen()")
> Cc: Jiri Slaby <jslaby@suse.com>
> Reported-by: Lukas F. Hartmann <lukas@mntmn.com>
> Tested-by: Lukas F. Hartmann <lukas@mntmn.com>
> Cc: stable <stable@vger.kernel.org>
> Signed-off-by: Dmitry Safonov <dima@arista.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> (cherry picked from commit d3736d82e8169768218ee0ef68718875918091a0)
> Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
> ---
> 
> The commits being fixed got requested via LP: #1791758 but
> were missing this follow-up.  Compile-tested on Xenial.
> 
> -Stefan
> 
>  drivers/tty/tty_io.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index bfe9ad85b362..23c6fd238422 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1256,7 +1256,8 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *
>  static int tty_reopen(struct tty_struct *tty)
>  {
>  	struct tty_driver *driver = tty->driver;
> -	int retval;
> +	struct tty_ldisc *ld;
> +	int retval = 0;
>  
>  	if (driver->type == TTY_DRIVER_TYPE_PTY &&
>  	    driver->subtype == PTY_TYPE_MASTER)
> @@ -1268,13 +1269,18 @@ static int tty_reopen(struct tty_struct *tty)
>  	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
>  		return -EBUSY;
>  
> -	retval = tty_ldisc_lock(tty, 5 * HZ);
> -	if (retval)
> -		return retval;
> +	ld = tty_ldisc_ref_wait(tty);
> +	if (ld) {
> +		tty_ldisc_deref(ld);
> +	} else {
> +		retval = tty_ldisc_lock(tty, 5 * HZ);
> +		if (retval)
> +			return retval;
>  
> -	if (!tty->ldisc)
> -		retval = tty_ldisc_reinit(tty, tty->termios.c_line);
> -	tty_ldisc_unlock(tty);
> +		if (!tty->ldisc)
> +			retval = tty_ldisc_reinit(tty, tty->termios.c_line);
> +		tty_ldisc_unlock(tty);
> +	}
>  
>  	if (retval == 0)
>  		tty->count++;
> 

Cherry pick and a stable fix, so I'm good with this.

Acked-by: Colin Ian King <colin.king@canonical.com>
Khaled Elmously Feb. 1, 2019, 4:51 a.m. UTC | #2
On 2019-01-30 16:43:23 , Stefan Bader wrote:
> From: Dmitry Safonov <dima@arista.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1813873
> 
> Try to get reference for ldisc during tty_reopen().
> If ldisc present, we don't need to do tty_ldisc_reinit() and lock the
> write side for line discipline semaphore.
> Effectively, it optimizes fast-path for tty_reopen(), but more
> importantly it won't interrupt ongoing IO on the tty as no ldisc change
> is needed.
> Fixes user-visible issue when tty_reopen() interrupted login process for
> user with a long password, observed and reported by Lukas.
> 
> Fixes: c96cf923a98d ("tty: Don't block on IO when ldisc change is pending")
> Fixes: 83d817f41070 ("tty: Hold tty_ldisc_lock() during tty_reopen()")
> Cc: Jiri Slaby <jslaby@suse.com>
> Reported-by: Lukas F. Hartmann <lukas@mntmn.com>
> Tested-by: Lukas F. Hartmann <lukas@mntmn.com>
> Cc: stable <stable@vger.kernel.org>
> Signed-off-by: Dmitry Safonov <dima@arista.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> (cherry picked from commit d3736d82e8169768218ee0ef68718875918091a0)
> Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
> ---
> 
> The commits being fixed got requested via LP: #1791758 but
> were missing this follow-up.  Compile-tested on Xenial.
> 
> -Stefan
> 
>  drivers/tty/tty_io.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index bfe9ad85b362..23c6fd238422 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1256,7 +1256,8 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *
>  static int tty_reopen(struct tty_struct *tty)
>  {
>  	struct tty_driver *driver = tty->driver;
> -	int retval;
> +	struct tty_ldisc *ld;
> +	int retval = 0;
>  
>  	if (driver->type == TTY_DRIVER_TYPE_PTY &&
>  	    driver->subtype == PTY_TYPE_MASTER)
> @@ -1268,13 +1269,18 @@ static int tty_reopen(struct tty_struct *tty)
>  	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
>  		return -EBUSY;
>  
> -	retval = tty_ldisc_lock(tty, 5 * HZ);
> -	if (retval)
> -		return retval;
> +	ld = tty_ldisc_ref_wait(tty);
> +	if (ld) {
> +		tty_ldisc_deref(ld);
> +	} else {
> +		retval = tty_ldisc_lock(tty, 5 * HZ);
> +		if (retval)
> +			return retval;
>  
> -	if (!tty->ldisc)
> -		retval = tty_ldisc_reinit(tty, tty->termios.c_line);
> -	tty_ldisc_unlock(tty);
> +		if (!tty->ldisc)
> +			retval = tty_ldisc_reinit(tty, tty->termios.c_line);
> +		tty_ldisc_unlock(tty);
> +	}
>  
>  	if (retval == 0)
>  		tty->count++;

Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Khaled Elmously Feb. 1, 2019, 4:53 a.m. UTC | #3
On 2019-01-30 16:43:23 , Stefan Bader wrote:
> From: Dmitry Safonov <dima@arista.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1813873
> 
> Try to get reference for ldisc during tty_reopen().
> If ldisc present, we don't need to do tty_ldisc_reinit() and lock the
> write side for line discipline semaphore.
> Effectively, it optimizes fast-path for tty_reopen(), but more
> importantly it won't interrupt ongoing IO on the tty as no ldisc change
> is needed.
> Fixes user-visible issue when tty_reopen() interrupted login process for
> user with a long password, observed and reported by Lukas.
> 
> Fixes: c96cf923a98d ("tty: Don't block on IO when ldisc change is pending")
> Fixes: 83d817f41070 ("tty: Hold tty_ldisc_lock() during tty_reopen()")
> Cc: Jiri Slaby <jslaby@suse.com>
> Reported-by: Lukas F. Hartmann <lukas@mntmn.com>
> Tested-by: Lukas F. Hartmann <lukas@mntmn.com>
> Cc: stable <stable@vger.kernel.org>
> Signed-off-by: Dmitry Safonov <dima@arista.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> (cherry picked from commit d3736d82e8169768218ee0ef68718875918091a0)
> Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
> ---
> 
> The commits being fixed got requested via LP: #1791758 but
> were missing this follow-up.  Compile-tested on Xenial.
> 
> -Stefan
> 
>  drivers/tty/tty_io.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index bfe9ad85b362..23c6fd238422 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1256,7 +1256,8 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *
>  static int tty_reopen(struct tty_struct *tty)
>  {
>  	struct tty_driver *driver = tty->driver;
> -	int retval;
> +	struct tty_ldisc *ld;
> +	int retval = 0;
>  
>  	if (driver->type == TTY_DRIVER_TYPE_PTY &&
>  	    driver->subtype == PTY_TYPE_MASTER)
> @@ -1268,13 +1269,18 @@ static int tty_reopen(struct tty_struct *tty)
>  	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
>  		return -EBUSY;
>  
> -	retval = tty_ldisc_lock(tty, 5 * HZ);
> -	if (retval)
> -		return retval;
> +	ld = tty_ldisc_ref_wait(tty);
> +	if (ld) {
> +		tty_ldisc_deref(ld);
> +	} else {
> +		retval = tty_ldisc_lock(tty, 5 * HZ);
> +		if (retval)
> +			return retval;
>  
> -	if (!tty->ldisc)
> -		retval = tty_ldisc_reinit(tty, tty->termios.c_line);
> -	tty_ldisc_unlock(tty);
> +		if (!tty->ldisc)
> +			retval = tty_ldisc_reinit(tty, tty->termios.c_line);
> +		tty_ldisc_unlock(tty);
> +	}
>  
>  	if (retval == 0)
>  		tty->count++;
> -- 
> 2.17.1
> 
> 
> -- 
> kernel-team mailing list
> kernel-team@lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

Patch
diff mbox series

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index bfe9ad85b362..23c6fd238422 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1256,7 +1256,8 @@  static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *
 static int tty_reopen(struct tty_struct *tty)
 {
 	struct tty_driver *driver = tty->driver;
-	int retval;
+	struct tty_ldisc *ld;
+	int retval = 0;
 
 	if (driver->type == TTY_DRIVER_TYPE_PTY &&
 	    driver->subtype == PTY_TYPE_MASTER)
@@ -1268,13 +1269,18 @@  static int tty_reopen(struct tty_struct *tty)
 	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
 		return -EBUSY;
 
-	retval = tty_ldisc_lock(tty, 5 * HZ);
-	if (retval)
-		return retval;
+	ld = tty_ldisc_ref_wait(tty);
+	if (ld) {
+		tty_ldisc_deref(ld);
+	} else {
+		retval = tty_ldisc_lock(tty, 5 * HZ);
+		if (retval)
+			return retval;
 
-	if (!tty->ldisc)
-		retval = tty_ldisc_reinit(tty, tty->termios.c_line);
-	tty_ldisc_unlock(tty);
+		if (!tty->ldisc)
+			retval = tty_ldisc_reinit(tty, tty->termios.c_line);
+		tty_ldisc_unlock(tty);
+	}
 
 	if (retval == 0)
 		tty->count++;