From: Jan H. Schönherr <jschoenh@amazon.de>
Date: Mon, 4 Sep 2017 14:00:50 +0000 (+0200)
Subject: vgacon: Prevent faulty bootparams.screeninfo from causing harm
X-Git-Tag: v4.14-rc1~25^2~5
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=b9a58de545858ac9ee67745cdea6d94cc322938e;p=linux-block.git

vgacon: Prevent faulty bootparams.screeninfo from causing harm

If a zero for the number of colums or rows manages to slip through,
gotoxy() will underflow vc->vc_pos, causing the next action on the
referenced memory to end with a page fault.

Make the check in vgacon_startup() more pessimistic to prevent that.

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
---

diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index dc06cb6a15dc..445b1dc5d441 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -398,9 +398,8 @@ static const char *vgacon_startup(void)
 #endif
 	}
 
-	/* boot_params.screen_info initialized? */
-	if ((screen_info.orig_video_mode  == 0) &&
-	    (screen_info.orig_video_lines == 0) &&
+	/* boot_params.screen_info reasonably initialized? */
+	if ((screen_info.orig_video_lines == 0) ||
 	    (screen_info.orig_video_cols  == 0))
 		goto no_vga;