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Subject[PATCH 4.9 19/44] tty: Handle problem if line discipline does not have receive_buf
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit 27cfb3a53be46a54ec5e0bd04e51995b74c90343 upstream.

Some tty line disciplines do not have a receive buf callback, so
properly check for that before calling it. If they do not have this
callback, just eat the character quietly, as we can't fail this call.

Reported-by: Jann Horn <jannh@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/tty/tty_io.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2324,7 +2324,8 @@ static int tiocsti(struct tty_struct *tt
ld = tty_ldisc_ref_wait(tty);
if (!ld)
return -EIO;
- ld->ops->receive_buf(tty, &ch, &mbz, 1);
+ if (ld->ops->receive_buf)
+ ld->ops->receive_buf(tty, &ch, &mbz, 1);
tty_ldisc_deref(ld);
return 0;
}

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