4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: DaeRyong Jeong threeearcat@gmail.com
[ Upstream commit b6da31b2c07c46f2dcad1d86caa835227a16d9ff ]
Unlike normal serials, in pty layer, there is no guarantee that multiple threads don't insert input characters at the same time. If it is happened, tty_insert_flip_string_fixed_flag can be executed concurrently. This can lead slab out-of-bounds write in tty_insert_flip_string_fixed_flag.
Call sequences are as follows. CPU0 CPU1 n_tty_ioctl_helper n_tty_ioctl_helper __start_tty tty_send_xchar tty_wakeup pty_write n_hdlc_tty_wakeup tty_insert_flip_string n_hdlc_send_frames tty_insert_flip_string_fixed_flag pty_write tty_insert_flip_string tty_insert_flip_string_fixed_flag
To fix the race, acquire port->lock in pty_write() before it inserts input characters to tty buffer. It prevents multiple threads from inserting input characters concurrently.
The crash log is as follows: BUG: KASAN: slab-out-of-bounds in tty_insert_flip_string_fixed_flag+0xb5/ 0x130 drivers/tty/tty_buffer.c:316 at addr ffff880114fcc121 Write of size 1792 by task syz-executor0/30017 CPU: 1 PID: 30017 Comm: syz-executor0 Not tainted 4.8.0 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014 0000000000000000 ffff88011638f888 ffffffff81694cc3 ffff88007d802140 ffff880114fcb300 ffff880114fcc300 ffff880114fcb300 ffff88011638f8b0 ffffffff8130075c ffff88011638f940 ffff88007d802140 ffff880194fcc121 Call Trace: __dump_stack lib/dump_stack.c:15 [inline] dump_stack+0xb3/0x110 lib/dump_stack.c:51 kasan_object_err+0x1c/0x70 mm/kasan/report.c:156 print_address_description mm/kasan/report.c:194 [inline] kasan_report_error+0x1f7/0x4e0 mm/kasan/report.c:283 kasan_report+0x36/0x40 mm/kasan/report.c:303 check_memory_region_inline mm/kasan/kasan.c:292 [inline] check_memory_region+0x13e/0x1a0 mm/kasan/kasan.c:299 memcpy+0x37/0x50 mm/kasan/kasan.c:335 tty_insert_flip_string_fixed_flag+0xb5/0x130 drivers/tty/tty_buffer.c:316 tty_insert_flip_string include/linux/tty_flip.h:35 [inline] pty_write+0x7f/0xc0 drivers/tty/pty.c:115 n_hdlc_send_frames+0x1d4/0x3b0 drivers/tty/n_hdlc.c:419 n_hdlc_tty_wakeup+0x73/0xa0 drivers/tty/n_hdlc.c:496 tty_wakeup+0x92/0xb0 drivers/tty/tty_io.c:601 __start_tty.part.26+0x66/0x70 drivers/tty/tty_io.c:1018 __start_tty+0x34/0x40 drivers/tty/tty_io.c:1013 n_tty_ioctl_helper+0x146/0x1e0 drivers/tty/tty_ioctl.c:1138 n_hdlc_tty_ioctl+0xb3/0x2b0 drivers/tty/n_hdlc.c:794 tty_ioctl+0xa85/0x16d0 drivers/tty/tty_io.c:2992 vfs_ioctl fs/ioctl.c:43 [inline] do_vfs_ioctl+0x13e/0xba0 fs/ioctl.c:679 SYSC_ioctl fs/ioctl.c:694 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685 entry_SYSCALL_64_fastpath+0x1f/0xbd
Signed-off-by: DaeRyong Jeong threeearcat@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/pty.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -106,16 +106,19 @@ static void pty_unthrottle(struct tty_st static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c) { struct tty_struct *to = tty->link; + unsigned long flags;
if (tty->stopped) return 0;
if (c > 0) { + spin_lock_irqsave(&to->port->lock, flags); /* Stuff the data into the input queue of the other end */ c = tty_insert_flip_string(to->port, buf, c); /* And shovel */ if (c) tty_flip_buffer_push(to->port); + spin_unlock_irqrestore(&to->port->lock, flags); } return c; }