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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Or Cohen <orcohen@paloaltonetworks.com>,
        Nicolas Pitre <npitre@baylibre.com>,
        Jiri Slaby <jslaby@suse.com>
Subject: [PATCH 4.19 241/243] vcs: prevent write access to vcsu devices
Date:   Wed, 11 Dec 2019 16:06:43 +0100
Message-Id: <20191211150355.607717902@linuxfoundation.org>
In-Reply-To: <20191211150339.185439726@linuxfoundation.org>
References: <20191211150339.185439726@linuxfoundation.org>
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From: Nicolas Pitre <nico@fluxnic.net>

commit 0c9acb1af77a3cb8707e43f45b72c95266903cee upstream.

Commit d21b0be246bf ("vt: introduce unicode mode for /dev/vcs") guarded
against using devices containing attributes as this is not yet
implemented. It however failed to guard against writes to any devices
as this is also unimplemented.

Reported-by: Or Cohen <orcohen@paloaltonetworks.com>
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Cc: <stable@vger.kernel.org> # v4.19+
Cc: Jiri Slaby <jslaby@suse.com>
Fixes: d21b0be246bf ("vt: introduce unicode mode for /dev/vcs")
Link: https://lore.kernel.org/r/nycvar.YSQ.7.76.1911051030580.30289@knanqh.ubzr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/vt/vc_screen.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -437,6 +437,9 @@ vcs_write(struct file *file, const char
 	size_t ret;
 	char *con_buf;
 
+	if (use_unicode(inode))
+		return -EOPNOTSUPP;
+
 	con_buf = (char *) __get_free_page(GFP_KERNEL);
 	if (!con_buf)
 		return -ENOMEM;