From: Jan H. Schönherr <jschoenh@amazon.de>
Date: Sun, 27 Aug 2017 18:23:43 +0000 (+0200)
Subject: x86/boot: Prevent faulty bootparams.screeninfo from causing harm
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=fb1cc2f91664fd8a2e454970480b5413725919f1;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git

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@amazon.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1503858223-14983-1-git-send-email-jschoenh@amazon.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index a0838ab929f2..c14217cd0155 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;