x86/video: Don't assume all FB devices are PCI devices

vittyvk · Ingo Molnar · commit 743146db071c · 2016-03-15T11:08:26.000+01:00
When booting Hyper-V Generation 2 guests KASAN reports the following out-of-bounds access: BUG: KASAN: slab-out-of-bounds in fb_is_primary_device+0x58/0x70 at addr ffff880079cf0eb0 Read of size 8 by task swapper/0/1 ... [<ffffffff81581308>] dump_stack+0x63/0x8b [<ffffffff812e1f99>] print_trailer+0xf9/0x150 [<ffffffff812e7344>] object_err+0x34/0x40 [<ffffffff812e9630>] kasan_report_error+0x230/0x550 [<ffffffff812e9ee8>] kasan_report+0x58/0x60 [<ffffffff812e4500>] ? ___slab_alloc+0x80/0x490 [<ffffffff81878a28>] ? fb_is_primary_device+0x58/0x70 [<ffffffff812e87cd>] __asan_load8+0x5d/0x70 [<ffffffff81878a28>] fb_is_primary_device+0x58/0x70 [<ffffffff8162357a>] register_framebuffer+0xda/0x5b0 [<ffffffff816234a0>] ? remove_conflicting_framebuffers+0x50/0x50 ... The issue is caused by the to_pci_dev() call with no check that the given info->device is in fact a PCI device and some FB devices (Hyper-V FB, EFI FB,...) are not. While on it, clean up the function. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Acked-by: Bjorn Helgaas <bhelgaas@google.com> Cc: Bjorn Helgaas <helgaas@kernel.org> Cc: Cathy Avery <cavery@redhat.com> Cc: K. Y. Srinivasan <kys@microsoft.com> 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/1458030033-10122-1-git-send-email-vkuznets@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/video/fbdev.c b/arch/x86/video/fbdev.c
@@ -14,26 +14,24 @@
 int fb_is_primary_device(struct fb_info *info)
 {
 	struct device *device = info->device;
-	struct pci_dev *pci_dev = NULL;
 	struct pci_dev *default_device = vga_default_device();
-	struct resource *res = NULL;
+	struct pci_dev *pci_dev;
+	struct resource *res;
 
-	if (device)
-		pci_dev = to_pci_dev(device);
-
-	if (!pci_dev)
+	if (!device || !dev_is_pci(device))
 		return 0;
 
+	pci_dev = to_pci_dev(device);
+
 	if (default_device) {
 		if (pci_dev == default_device)
 			return 1;
-		else
-			return 0;
+		return 0;
 	}
 
-	res = &pci_dev->resource[PCI_ROM_RESOURCE];
+	res = pci_dev->resource + PCI_ROM_RESOURCE;
 
-	if (res && res->flags & IORESOURCE_ROM_SHADOW)
+	if (res->flags & IORESOURCE_ROM_SHADOW)
 		return 1;
 
 	return 0;
