linux-kernel - [PATCH 4.4 26/41] PCI: Fix race condition with driver

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Message-Id: <20171003114221.518347361@linuxfoundation.org>
Date:   Tue,  3 Oct 2017 14:21:27 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nicolai Stange <nstange@...e.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH 4.4 26/41] PCI: Fix race condition with driver_override

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolai Stange <nstange@...e.de>

commit 9561475db680f7144d2223a409dd3d7e322aca03 upstream.

The driver_override implementation is susceptible to a race condition when
different threads are reading vs. storing a different driver override.  Add
locking to avoid the race condition.

This is in close analogy to commit 6265539776a0 ("driver core: platform:
fix race condition with driver_override") from Adrian Salido.

Fixes: 782a985d7af2 ("PCI: Introduce new device binding path using pci_dev.driver_override")
Signed-off-by: Nicolai Stange <nstange@...e.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/pci/pci-sysfs.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -522,7 +522,7 @@ static ssize_t driver_override_store(str
 				     const char *buf, size_t count)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
-	char *driver_override, *old = pdev->driver_override, *cp;
+	char *driver_override, *old, *cp;
 
 	/* We need to keep extra room for a newline */
 	if (count >= (PAGE_SIZE - 1))
@@ -536,12 +536,15 @@ static ssize_t driver_override_store(str
 	if (cp)
 		*cp = '\0';
 
+	device_lock(dev);
+	old = pdev->driver_override;
 	if (strlen(driver_override)) {
 		pdev->driver_override = driver_override;
 	} else {
 		kfree(driver_override);
 		pdev->driver_override = NULL;
 	}
+	device_unlock(dev);
 
 	kfree(old);
 
@@ -552,8 +555,12 @@ static ssize_t driver_override_show(stru
 				    struct device_attribute *attr, char *buf)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
+	ssize_t len;
 
-	return snprintf(buf, PAGE_SIZE, "%s\n", pdev->driver_override);
+	device_lock(dev);
+	len = snprintf(buf, PAGE_SIZE, "%s\n", pdev->driver_override);
+	device_unlock(dev);
+	return len;
 }
 static DEVICE_ATTR_RW(driver_override);