[PATCH] ttyprintk: fix a potential sleeping in interrupt context issue

[PATCH] ttyprintk: fix a potential sleeping in interrupt context issue

[Zhenzhong Duan]

Google syzbot reports:
BUG: sleeping function called from invalid context at
kernel/locking/mutex.c:938
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
1 lock held by swapper/1/0:
...
Call Trace:
  <IRQ>
  dump_stack+0x197/0x210
  ___might_sleep.cold+0x1fb/0x23e
  __might_sleep+0x95/0x190
  __mutex_lock+0xc5/0x13c0
  mutex_lock_nested+0x16/0x20
  tpk_write+0x5d/0x340
  resync_tnc+0x1b6/0x320
  call_timer_fn+0x1ac/0x780
  run_timer_softirq+0x6c3/0x1790
  __do_softirq+0x262/0x98c
  irq_exit+0x19b/0x1e0
  smp_apic_timer_interrupt+0x1a3/0x610
  apic_timer_interrupt+0xf/0x20
  </IRQ>

This patch fix it by using spinlock in process context instead of
mutex and having interrupt disabled in critical section.

Reported-by: syzbot+2eeef62ee31f9460ad65@syzkaller.appspotmail.com
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 drivers/char/ttyprintk.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
index 4f24e46ebe7c..56db949a7b70 100644
--- a/drivers/char/ttyprintk.c
+++ b/drivers/char/ttyprintk.c
@@ -15,10 +15,11 @@
 #include <linux/serial.h>
 #include <linux/tty.h>
 #include <linux/module.h>
+#include <linux/spinlock.h>

 struct ttyprintk_port {
  struct tty_port port;
- struct mutex port_write_mutex;
+ spinlock_t spinlock;
 };

 static struct ttyprintk_port tpk_port;
@@ -99,11 +100,12 @@ static int tpk_open(struct tty_struct *tty,
struct file *filp)
 static void tpk_close(struct tty_struct *tty, struct file *filp)
 {
  struct ttyprintk_port *tpkp = tty->driver_data;
+ unsigned long flags;

- mutex_lock(&tpkp->port_write_mutex);
+ spin_lock_irqsave(&tpkp->spinlock, flags);
  /* flush tpk_printk buffer */
  tpk_printk(NULL, 0);
- mutex_unlock(&tpkp->port_write_mutex);
+ spin_unlock_irqrestore(&tpkp->spinlock, flags);

  tty_port_close(&tpkp->port, tty, filp);
 }
@@ -115,13 +117,14 @@ static int tpk_write(struct tty_struct *tty,
  const unsigned char *buf, int count)
 {
  struct ttyprintk_port *tpkp = tty->driver_data;
+ unsigned long flags;
  int ret;


  /* exclusive use of tpk_printk within this tty */
- mutex_lock(&tpkp->port_write_mutex);
+ spin_lock_irqsave(&tpkp->spinlock, flags);
  ret = tpk_printk(buf, count);
- mutex_unlock(&tpkp->port_write_mutex);
+ spin_unlock_irqrestore(&tpkp->spinlock, flags);

  return ret;
 }
@@ -171,7 +174,7 @@ static int __init ttyprintk_init(void)
 {
  int ret = -ENOMEM;

- mutex_init(&tpk_port.port_write_mutex);
+ spin_lock_init(&tpk_port.spinlock);

  ttyprintk_driver = tty_alloc_driver(1,
  TTY_DRIVER_RESET_TERMIOS |
--
2.23.0

Re: [PATCH] ttyprintk: fix a potential sleeping in interrupt context issue

[Greg KH]

On Wed, Dec 11, 2019 at 09:11:46PM +0800, Zhenzhong Duan wrote:
> Google syzbot reports:
> BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:938
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
> 1 lock held by swapper/1/0:
> ...
> Call Trace:
>   <IRQ>
>   dump_stack+0x197/0x210
>   ___might_sleep.cold+0x1fb/0x23e
>   __might_sleep+0x95/0x190
>   __mutex_lock+0xc5/0x13c0
>   mutex_lock_nested+0x16/0x20
>   tpk_write+0x5d/0x340
>   resync_tnc+0x1b6/0x320
>   call_timer_fn+0x1ac/0x780
>   run_timer_softirq+0x6c3/0x1790
>   __do_softirq+0x262/0x98c
>   irq_exit+0x19b/0x1e0
>   smp_apic_timer_interrupt+0x1a3/0x610
>   apic_timer_interrupt+0xf/0x20
>   </IRQ>
> 
> This patch fix it by using spinlock in process context instead of
> mutex and having interrupt disabled in critical section.
> 
> Reported-by: syzbot+2eeef62ee31f9460ad65@syzkaller.appspotmail.com
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> ---
>  drivers/char/ttyprintk.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
> index 4f24e46ebe7c..56db949a7b70 100644
> --- a/drivers/char/ttyprintk.c
> +++ b/drivers/char/ttyprintk.c
> @@ -15,10 +15,11 @@
>  #include <linux/serial.h>
>  #include <linux/tty.h>
>  #include <linux/module.h>
> +#include <linux/spinlock.h>
> 
>  struct ttyprintk_port {
>   struct tty_port port;
> - struct mutex port_write_mutex;
> + spinlock_t spinlock;
>  };
> 
>  static struct ttyprintk_port tpk_port;
> @@ -99,11 +100,12 @@ static int tpk_open(struct tty_struct *tty,
> struct file *filp)
>  static void tpk_close(struct tty_struct *tty, struct file *filp)
>  {
>   struct ttyprintk_port *tpkp = tty->driver_data;
> + unsigned long flags;
> 
> - mutex_lock(&tpkp->port_write_mutex);
> + spin_lock_irqsave(&tpkp->spinlock, flags);
>   /* flush tpk_printk buffer */
>   tpk_printk(NULL, 0);
> - mutex_unlock(&tpkp->port_write_mutex);
> + spin_unlock_irqrestore(&tpkp->spinlock, flags);
> 
>   tty_port_close(&tpkp->port, tty, filp);
>  }


Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- Your patch is malformed (tabs converted to spaces, linewrapped, etc.)
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If you wish to discuss this problem further, or you have questions about
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thanks,

greg k-h's patch email bot