linux-kernel - [PATCH] PCI/sysfs: off by two and memory corruption in driver

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Date:	Thu,  1 Jan 2015 19:27:12 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	linux-kernel@...r.kernel.org
Cc:	gregkh@...uxfoundation.org, Sasha Levin <sasha.levin@...cle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci@...r.kernel.org (open list:PCI SUBSYSTEM)
Subject: [PATCH] PCI/sysfs: off by two and memory corruption in driver_override parameter

There are two different issues fixed here:

 - On nun-NULL terminated input a random byte of memory would get flipped
from '\n' to '\0'.
 - When printing the driver_override parameter when it is 4095 and 4094 bytes
long the printing code would access invalid memory.

Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
---
 drivers/pci/pci-sysfs.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index aa012fb..be6b2b1 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -521,17 +521,17 @@ 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);
 	if (!driver_override)
 		return -ENOMEM;
 
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
+	driver_override[count] = '\0';
+	if (driver_override[count - 1] == '\n')
+		driver_override[count - 1] = 0;
 	if (strlen(driver_override)) {
 		pdev->driver_override = driver_override;
 	} else {
-- 
1.7.10.4

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