forked from Minki/linux
925bb1ce47
tty_insert_flip_string_fixed_flag() is racy against itself when called
from the ioctl(TCXONC, TCION/TCIOFF) path [1] and the flush_to_ldisc()
workqueue path [2].
The problem is that port->buf.tail->used is modified without consistent
locking; the ioctl path takes tty->atomic_write_lock, whereas the workqueue
path takes ldata->output_lock.
We cannot simply take ldata->output_lock, since that is specific to the
N_TTY line discipline.
It might seem natural to try to take port->buf.lock inside
tty_insert_flip_string_fixed_flag() and friends (where port->buf is
actually used/modified), but this creates problems for flush_to_ldisc()
which takes it before grabbing tty->ldisc_sem, o_tty->termios_rwsem,
and ldata->output_lock.
Therefore, the simplest solution for now seems to be to take
tty->atomic_write_lock inside tty_port_default_receive_buf(). This lock
is also used in the write path [3] with a consistent ordering.
[1]: Call Trace:
tty_insert_flip_string_fixed_flag
pty_write
tty_send_xchar // down_read(&o_tty->termios_rwsem)
// mutex_lock(&tty->atomic_write_lock)
n_tty_ioctl_helper
n_tty_ioctl
tty_ioctl // down_read(&tty->ldisc_sem)
do_vfs_ioctl
SyS_ioctl
[2]: Workqueue: events_unbound flush_to_ldisc
Call Trace:
tty_insert_flip_string_fixed_flag
pty_write
tty_put_char
__process_echoes
commit_echoes // mutex_lock(&ldata->output_lock)
n_tty_receive_buf_common
n_tty_receive_buf2
tty_ldisc_receive_buf // down_read(&o_tty->termios_rwsem)
tty_port_default_receive_buf // down_read(&tty->ldisc_sem)
flush_to_ldisc // mutex_lock(&port->buf.lock)
process_one_work
[3]: Call Trace:
tty_insert_flip_string_fixed_flag
pty_write
n_tty_write // mutex_lock(&ldata->output_lock)
// down_read(&tty->termios_rwsem)
do_tty_write (inline) // mutex_lock(&tty->atomic_write_lock)
tty_write // down_read(&tty->ldisc_sem)
__vfs_write
vfs_write
SyS_write
The bug can result in about a dozen different crashes depending on what
exactly gets corrupted when port->buf.tail->used points outside the
buffer.
The patch passes my LOCKDEP/PROVE_LOCKING testing but more testing is
always welcome.
Found using syzkaller.
Cc: <stable@vger.kernel.org>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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| .. | ||
| hvc | ||
| ipwireless | ||
| serdev | ||
| serial | ||
| vt | ||
| amiserial.c | ||
| bfin_jtag_comm.c | ||
| cyclades.c | ||
| ehv_bytechan.c | ||
| goldfish.c | ||
| isicom.c | ||
| Kconfig | ||
| Makefile | ||
| metag_da.c | ||
| mips_ejtag_fdc.c | ||
| moxa.c | ||
| moxa.h | ||
| mxser.c | ||
| mxser.h | ||
| n_gsm.c | ||
| n_hdlc.c | ||
| n_r3964.c | ||
| n_tracerouter.c | ||
| n_tracesink.c | ||
| n_tracesink.h | ||
| n_tty.c | ||
| nozomi.c | ||
| pty.c | ||
| rocket_int.h | ||
| rocket.c | ||
| rocket.h | ||
| synclink_gt.c | ||
| synclink.c | ||
| synclinkmp.c | ||
| sysrq.c | ||
| tty_audit.c | ||
| tty_baudrate.c | ||
| tty_buffer.c | ||
| tty_io.c | ||
| tty_ioctl.c | ||
| tty_jobctrl.c | ||
| tty_ldisc.c | ||
| tty_ldsem.c | ||
| tty_mutex.c | ||
| tty_port.c | ||