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 a0838ab929f2276de8ed08e2e0430f4e3e7943f8..c14217cd0155f09ab7f00e018ec25fe3b4c4cf5e 100644 (file)
--- 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;