[PATCH v3] x86: don't assume all fb devices are PCI devices

[Vitaly Kuznetsov]

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, cleanup the function.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
Changes since v2: cleanup fb_is_primary_device() [Bjorn Helgaas, Ingo Molnar].
---
 arch/x86/video/fbdev.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/x86/video/fbdev.c b/arch/x86/video/fbdev.c
index d5644bb..9fd2484 100644
--- 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;
-- 
2.5.0