linux-kernel - [PATCH AUTOSEL 4.19 035/252] x86/sysfb: Fix check for bad VRAM size

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Date:   Fri, 14 Feb 2020 11:08:10 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Christopher Head <chead@...ad.ca>,
        Borislav Petkov <bp@...e.de>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.19 035/252] x86/sysfb: Fix check for bad VRAM size

From: Arvind Sankar <nivedita@...m.mit.edu>

[ Upstream commit dacc9092336be20b01642afe1a51720b31f60369 ]

When checking whether the reported lfb_size makes sense, the height
* stride result is page-aligned before seeing whether it exceeds the
reported size.

This doesn't work if height * stride is not an exact number of pages.
For example, as reported in the kernel bugzilla below, an 800x600x32 EFI
framebuffer gets skipped because of this.

Move the PAGE_ALIGN to after the check vs size.

Reported-by: Christopher Head <chead@...ad.ca>
Tested-by: Christopher Head <chead@...ad.ca>
Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206051
Link: https://lkml.kernel.org/r/20200107230410.2291947-1-nivedita@alum.mit.edu
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 85195d447a922..f3215346e47fd 100644
--- a/arch/x86/kernel/sysfb_simplefb.c
+++ b/arch/x86/kernel/sysfb_simplefb.c
@@ -94,11 +94,11 @@ __init int create_simplefb(const struct screen_info *si,
 	if (si->orig_video_isVGA == VIDEO_TYPE_VLFB)
 		size <<= 16;
 	length = mode->height * mode->stride;
-	length = PAGE_ALIGN(length);
 	if (length > size) {
 		printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
 		return -EINVAL;
 	}
+	length = PAGE_ALIGN(length);
 
 	/* setup IORESOURCE_MEM as framebuffer memory */
 	memset(&res, 0, sizeof(res));
-- 
2.20.1