linux-kernel - [PATCH] vt: Clear selection before changing the font

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Message-ID: <YuV9apZGNmGfjcor@p100>
Date:   Sat, 30 Jul 2022 20:50:18 +0200
From:   Helge Deller <deller@....de>
To:     Khalid Masum <khalid.masum.92@...il.com>,
        syzbot <syzbot+14b0e8f3fd1612e35350@...kaller.appspotmail.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: [PATCH] vt: Clear selection before changing the font

When changing the console font with ioctl(KDFONTOP) the new font size
can be bigger than the previous font. A previous selection may thus now
be outside of the new screen size and thus trigger out-of-bounds
accesses to graphics memory if the selection is removed in
vc_do_resize().

Prevent such out-of-memory accesses by dropping the selection before the
various con_font_set() console handlers are called.

Signed-off-by: Helge Deller <deller@....de>
Reported-by: syzbot+14b0e8f3fd1612e35350@...kaller.appspotmail.com

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index dfc1f4b445f3..3f09205185a4 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -4662,9 +4662,11 @@ static int con_font_set(struct vc_data *vc, struct console_font_op *op)
 	console_lock();
 	if (vc->vc_mode != KD_TEXT)
 		rc = -EINVAL;
-	else if (vc->vc_sw->con_font_set)
+	else if (vc->vc_sw->con_font_set) {
+		if (vc_is_sel(vc))
+			clear_selection();
 		rc = vc->vc_sw->con_font_set(vc, &font, op->flags);
-	else
+	} else
 		rc = -ENOSYS;
 	console_unlock();
 	kfree(font.data);
@@ -4691,9 +4693,11 @@ static int con_font_default(struct vc_data *vc, struct console_font_op *op)
 		console_unlock();
 		return -EINVAL;
 	}
-	if (vc->vc_sw->con_font_default)
+	if (vc->vc_sw->con_font_default) {
+		if (vc_is_sel(vc))
+			clear_selection();
 		rc = vc->vc_sw->con_font_default(vc, &font, s);
-	else
+	} else
 		rc = -ENOSYS;
 	console_unlock();
 	if (!rc) {