[PATCH v2] PCI/sysfs: off by two when checking the limit on driver_override length

[Sasha Levin]

When printing the driver_override parameter when it is 4095 and 4094 bytes
long the printing code would access invalid memory because we need count+1
bytes for printing.

Cc: <stable@xxxxxxxxxxxxxxx> # v3.16+
Fixes: 782a985d ("PCI: Introduce new device binding path using pci_dev.driver_override")
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Alexander Graf <agraf@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 drivers/pci/pci-sysfs.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index aa012fb..17459ed 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -521,7 +521,8 @@ static ssize_t driver_override_store(struct device *dev,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	char *driver_override, *old = pdev->driver_override, *cp;
 
-	if (count > PATH_MAX)
+	/* We need to keep extra room for a newline */
+	if (count >= (PATH_MAX - 1))
 		return -EINVAL;
 
 	driver_override = kstrndup(buf, count, GFP_KERNEL);
-- 
1.7.10.4

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