linux-kernel - [PATCH] x86/boot: Prevent faulty bootparams.screeninfo from causing harm

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Message-Id: <1503858223-14983-1-git-send-email-jschoenh@amazon.de>
Date:   Sun, 27 Aug 2017 20:23:43 +0200
From:   Jan H. Schönherr <jschoenh@...zon.de>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Jan H. Schönherr <jschoenh@...zon.de>
Subject: [PATCH] x86/boot: Prevent faulty bootparams.screeninfo from causing harm

If a zero for the number of lines manages to slip through, scroll()
may underflow some offset calculations, causing accesses outside the
video memory.

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

Signed-off-by: Jan H. Schönherr <jschoenh@...zon.de>
---
 arch/x86/boot/compressed/misc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index a0838ab..c14217c 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -116,8 +116,7 @@ void __putstr(const char *s)
 		}
 	}
 
-	if (boot_params->screen_info.orig_video_mode == 0 &&
-	    lines == 0 && cols == 0)
+	if (lines == 0 || cols == 0)
 		return;
 
 	x = boot_params->screen_info.orig_x;
-- 
2.3.1.dirty