linux-kernel - [PATCH v3] x86: simplefb: avoid overflow

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Message-Id: <1380644320-1026-1-git-send-email-teg@jklm.no>
Date:	Tue,  1 Oct 2013 18:18:40 +0200
From:	Tom Gundersen <teg@...m.no>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Tom Gundersen <teg@...m.no>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Stephen Warren <swarren@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v3] x86: simplefb: avoid overflow

On my MacBook Air lfb_size is 4M, which makes the bitshit overflow, meaning we
fall back to efifb unnecessarily.

Cast to u64 to avoid the overflow.

Signed-off-by: Tom Gundersen <teg@...m.no>
Reviewed-by: David Herrmann <dh.herrmann@...il.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Stephen Warren <swarren@...dia.com>,
Cc: Stephen Warren <swarren@...dotorg.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
v2: use (__u64) rather than (unsigned long). This is strictly speaking not
    necessary, but as David poited out it makes it more obvious that we
    we won't have problems on 32bit.
v3: remove superfluous parens and use (u64) rather than (__64) as this is not
    shared by userspace.

 arch/x86/kernel/sysfb_simplefb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sysfb_simplefb.c b/arch/x86/kernel/sysfb_simplefb.c
index 22513e9..4ebd636 100644
--- a/arch/x86/kernel/sysfb_simplefb.c
+++ b/arch/x86/kernel/sysfb_simplefb.c
@@ -72,7 +72,7 @@ __init int create_simplefb(const struct screen_info *si,
 	 * the part that is occupied by the framebuffer */
 	len = mode->height * mode->stride;
 	len = PAGE_ALIGN(len);
-	if (len > si->lfb_size << 16) {
+	if (len > (u64)si->lfb_size << 16) {
 		printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
 		return -EINVAL;
 	}
-- 
1.8.4

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