linux-kernel - [PATCH 3.12 118/212] tty: Reset hupped state on open

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Message-Id: <20131202191300.339003023@linuxfoundation.org>
Date:	Mon,  2 Dec 2013 11:15:09 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Heorhi Valakhanovich <valahanovich@....by>,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 3.12 118/212] tty: Reset hupped state on open

3.12-stable review patch.  If anyone has any objections, please let me know.

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

From: Peter Hurley <peter@...leysoftware.com>

commit d4855e1fc03c2bb32dd64badf51cec5a2a26ab2a upstream.

A common security idiom is to hangup the current tty (via vhangup())
after forking but before execing a root shell. This hangs up any
existing opens which other processes may have and ensures subsequent
opens have the necessary permissions to open the root shell tty/pty.

Reset the TTY_HUPPED state after the driver has successfully
returned the opened tty (perform the reset while the tty is locked
to avoid racing with concurrent hangups).

Reported-by: Heorhi Valakhanovich <valahanovich@....by>
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
Tested-by: Heorhi Valakhanovich <valahanovich@....by>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/tty_io.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2086,6 +2086,7 @@ retry_open:
 			filp->f_op = &tty_fops;
 		goto retry_open;
 	}
+	clear_bit(TTY_HUPPED, &tty->flags);
 	tty_unlock(tty);

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