[PATCH v2] pci: Fix infinite loop with ROM image of size 0

["Michel Dänzer" <michel@daenzer.net>]

From: Michel Dänzer <michel.daenzer@amd.com>

If the image size would ever read as 0, pci_get_rom_size could keep
processing the same image over and over again.

Reported-by: Federico <federicotg@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
---

v2:
* Use unsigned instead of u16 for the local length variable (not sure if
  the multiplication by 512 could overflow otherwise)
* Integrate length condition into while statement
* Add stable tag

 drivers/pci/rom.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/rom.c b/drivers/pci/rom.c
index f955edb..eb0ad53 100644
--- a/drivers/pci/rom.c
+++ b/drivers/pci/rom.c
@@ -71,6 +71,7 @@ size_t pci_get_rom_size(struct pci_dev *pdev, void __iomem *rom, size_t size)
 {
 	void __iomem *image;
 	int last_image;
+	unsigned length;
 
 	image = rom;
 	do {
@@ -93,9 +94,9 @@ size_t pci_get_rom_size(struct pci_dev *pdev, void __iomem *rom, size_t size)
 		if (readb(pds + 3) != 'R')
 			break;
 		last_image = readb(pds + 21) & 0x80;
-		/* this length is reliable */
-		image += readw(pds + 16) * 512;
-	} while (!last_image);
+		length = readw(pds + 16);
+		image += length * 512;
+	} while (length && !last_image);
 
 	/* never return a size larger than the PCI resource window */
 	/* there are known ROMs that get the size wrong */
-- 
2.1.4