From: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20200113034842.435-1-zhenzhong.duan@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/char/ttyprintk.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) --- 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 *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); } @@ -115,13 +117,14 @@ 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; } @@ -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 |
