From: Zhenzhong Duan zhenzhong.duan@gmail.com
commit 9a655c77ff8fc65699a3f98e237db563b37c439b upstream.
tpk_write()/tpk_close() could be interrupted when holding a mutex, then in timer handler tpk_write() may be called again trying to acquire same mutex, lead to deadlock.
Google syzbot reported this issue with CONFIG_DEBUG_ATOMIC_SLEEP enabled:
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>
See link https://syzkaller.appspot.com/bug?extid=2eeef62ee31f9460ad65 for more details.
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@gmail.com Cc: Arnd Bergmann arnd@arndb.de Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Link: https://lore.kernel.org/r/20200113034842.435-1-zhenzhong.duan@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/char/ttyprintk.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)
--- a/drivers/char/ttyprintk.c +++ b/drivers/char/ttyprintk.c @@ -18,10 +18,11 @@ #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; @@ -100,11 +101,12 @@ static int tpk_open(struct tty_struct *t 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); } @@ -116,13 +118,14 @@ static int tpk_write(struct tty_struct * 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; } @@ -172,7 +175,7 @@ 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 |