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tty: Hold termios_rwsem for tcflow(TCIxxx) 

While transmitting a START/STOP char for tcflow(TCION/TCIOFF), prevent
a termios change. Otherwise, a garbage in-band flow control char
may be sent, if the termios change overlaps the transmission setup.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2014-09-10 15:06:35 -04:00 committed by Greg Kroah-Hartman
parent 136d5258b2
commit c274f6ef1c
1 changed files with 7 additions and 3 deletions
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10
drivers/tty/tty_ioctl.c
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@ -1164,17 +1164,21 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
spin_unlock_irq(&tty->flow_lock); spin_unlock_irq(&tty->flow_lock);
break; break;
case TCIOFF: case TCIOFF:
down_read(&tty->termios_rwsem);
if (STOP_CHAR(tty) != __DISABLED_CHAR) if (STOP_CHAR(tty) != __DISABLED_CHAR)
return tty_send_xchar(tty, STOP_CHAR(tty)); retval = tty_send_xchar(tty, STOP_CHAR(tty));
up_read(&tty->termios_rwsem);
break; break;
case TCION: case TCION:
down_read(&tty->termios_rwsem);
if (START_CHAR(tty) != __DISABLED_CHAR) if (START_CHAR(tty) != __DISABLED_CHAR)
return tty_send_xchar(tty, START_CHAR(tty)); retval = tty_send_xchar(tty, START_CHAR(tty));
up_read(&tty->termios_rwsem);
break; break;
default: default:
return -EINVAL; return -EINVAL;
} }
return 0; return retval;
case TCFLSH: case TCFLSH:
retval = tty_check_change(tty); retval = tty_check_change(tty);
if (retval) if (retval)