Re: [PATCH] n_tty: Remove LINEMODE support

From: Howard Chu
Date: Sun Jan 18 2015 - 17:52:05 EST

Peter Hurley wrote:
Commit 26df6d13406d1 ("tty: Add EXTPROC support for LINEMODE") added
the undocumented EXTPROC input processing mode, which ignores the ICANON
setting and forces pty slave input to be processed in non-canonical
mode.

Although intended to provide a transparent mechanism for local line
edit with telnetd (and other remote shell protocols), the transparency
is limited.

Userspace usage is abandoned; telnetd does not even compile with
LINEMODE support. readline/bash and sshd never supported this.

I object to this. Code for all of the above exists and works. I use this code daily.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=585527
http://lists.gnu.org/archive/html/bug-readline/2011-01/msg00004.html
https://github.com/hyc/OpenSSH-LINEMODE

The lack of LINEMODE support in upstream sshd can only be considered a security hole.

http://www.metzdowd.com/pipermail/cryptography/2015-January/024288.html


Cc: Howard Chu <hyc@xxxxxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
drivers/tty/n_tty.c | 22 ++++++----------------
drivers/tty/pty.c | 24 +-----------------------
2 files changed, 7 insertions(+), 39 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index eb9f114..5120d2b 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1562,10 +1562,6 @@ n_tty_receive_buf_standard(struct tty_struct *tty, const unsigned char *cp,
c &= 0x7f;
if (I_IUCLC(tty) && L_IEXTEN(tty))
c = tolower(c);
- if (L_EXTPROC(tty)) {
- put_tty_queue(c, ldata);
- continue;
- }
if (!test_bit(c, ldata->char_map))
n_tty_receive_char_inline(tty, c);
else if (n_tty_receive_char_special(tty, c) && count) {
@@ -1613,9 +1609,9 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,

if (ldata->real_raw)
n_tty_receive_buf_real_raw(tty, cp, fp, count);
- else if (ldata->raw || (L_EXTPROC(tty) && !preops))
+ else if (ldata->raw)
n_tty_receive_buf_raw(tty, cp, fp, count);
- else if (tty->closing && !L_EXTPROC(tty))
+ else if (tty->closing)
n_tty_receive_buf_closing(tty, cp, fp, count);
else {
if (ldata->lnext) {
@@ -1637,13 +1633,13 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
tty->ops->flush_chars(tty);
}

- if (ldata->icanon && !L_EXTPROC(tty))
+ if (ldata->icanon)
return;

/* publish read_head to consumer */
smp_store_release(&ldata->commit_head, ldata->read_head);

- if ((read_cnt(ldata) >= ldata->minimum_to_wake) || L_EXTPROC(tty)) {
+ if (read_cnt(ldata) >= ldata->minimum_to_wake) {
kill_fasync(&tty->fasync, SIGIO, POLL_IN);
if (waitqueue_active(&tty->read_wait))
wake_up_interruptible_poll(&tty->read_wait, POLLIN);
@@ -1939,7 +1935,7 @@ static inline int input_available_p(struct tty_struct *tty, int poll)
struct n_tty_data *ldata = tty->disc_data;
int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;

- if (ldata->icanon && !L_EXTPROC(tty))
+ if (ldata->icanon)
return ldata->canon_head != ldata->read_tail;
else
return ldata->commit_head - ldata->read_tail >= amt;
@@ -1973,7 +1969,6 @@ static int copy_from_read_buf(struct tty_struct *tty,
struct n_tty_data *ldata = tty->disc_data;
int retval;
size_t n;
- bool is_eof;
size_t head = smp_load_acquire(&ldata->commit_head);
size_t tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1);

@@ -1983,14 +1978,9 @@ static int copy_from_read_buf(struct tty_struct *tty,
if (n) {
retval = copy_to_user(*b, read_buf_addr(ldata, tail), n);
n -= retval;
- is_eof = n == 1 && read_buf(ldata, tail) == EOF_CHAR(tty);
tty_audit_add_data(tty, read_buf_addr(ldata, tail), n,
ldata->icanon);
smp_store_release(&ldata->read_tail, ldata->read_tail + n);
- /* Turn single EOF into zero-length read */
- if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
- (head == ldata->read_tail))
- n = 0;
*b += n;
*nr -= n;
}
@@ -2257,7 +2247,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
continue;
}

- if (ldata->icanon && !L_EXTPROC(tty)) {
+ if (ldata->icanon) {
retval = canon_copy_from_read_buf(tty, &b, &nr);
if (retval == -EAGAIN) {
retval = 0;
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index ee06b77..01ac182 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -192,20 +192,6 @@ static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
return put_user(pktmode, arg);
}

-/* Send a signal to the slave */
-static int pty_signal(struct tty_struct *tty, int sig)
-{
- struct pid *pgrp;
-
- if (tty->link) {
- pgrp = tty_get_pgrp(tty->link);
- if (pgrp)
- kill_pgrp(pgrp, sig, 1);
- put_pid(pgrp);
- }
- return 0;
-}
-
static void pty_flush_buffer(struct tty_struct *tty)
{
struct tty_struct *to = tty->link;
@@ -254,15 +240,13 @@ static void pty_set_termios(struct tty_struct *tty,
{
/* See if packet mode change of state. */
if (tty->link && tty->link->packet) {
- int extproc = (old_termios->c_lflag & EXTPROC) |
- (tty->termios.c_lflag & EXTPROC);
int old_flow = ((old_termios->c_iflag & IXON) &&
(old_termios->c_cc[VSTOP] == '\023') &&
(old_termios->c_cc[VSTART] == '\021'));
int new_flow = (I_IXON(tty) &&
STOP_CHAR(tty) == '\023' &&
START_CHAR(tty) == '\021');
- if ((old_flow != new_flow) || extproc) {
+ if (old_flow != new_flow) {
spin_lock_irq(&tty->ctrl_lock);
if (old_flow != new_flow) {
tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
@@ -271,8 +255,6 @@ static void pty_set_termios(struct tty_struct *tty,
else
tty->ctrl_status |= TIOCPKT_NOSTOP;
}
- if (extproc)
- tty->ctrl_status |= TIOCPKT_IOCTL;
spin_unlock_irq(&tty->ctrl_lock);
wake_up_interruptible(&tty->link->read_wait);
}
@@ -482,8 +464,6 @@ static int pty_bsd_ioctl(struct tty_struct *tty,
return pty_set_pktmode(tty, (int __user *)arg);
case TIOCGPKT: /* Get PT packet mode */
return pty_get_pktmode(tty, (int __user *)arg);
- case TIOCSIG: /* Send signal to other side of pty */
- return pty_signal(tty, (int) arg);
case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
return -EINVAL;
}
@@ -607,8 +587,6 @@ static int pty_unix98_ioctl(struct tty_struct *tty,
return pty_get_pktmode(tty, (int __user *)arg);
case TIOCGPTN: /* Get PT Number */
return put_user(tty->index, (unsigned int __user *)arg);
- case TIOCSIG: /* Send signal to other side of pty */
- return pty_signal(tty, (int) arg);
}

return -ENOIOCTLCMD;



--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
--
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