[PATCH v4 00/11] Fix broken usage of driver_override (and kfree of static memory)

[PATCH v4 00/11] Fix broken usage of driver_override (and kfree of static memory)

[Krzysztof Kozlowski]

Hi,

This is a continuation of my old patchset from 2019. [1]
Back then, few drivers set driver_override wrong. I fixed Exynos
in a different way after discussions. QCOM NGD was not fixed
and a new user appeared - IMX SCU.

It seems "char *" in driver_override looks too consty, so we
tend to make a mistake of storing there string literals.

Changes since latest v3
=======================
1. Wrap comments, extend comment in driver_set_override() about newline.
2. Minor commit msg fixes.
3. Add tags.

Changes since latest v2
=======================
1. Make all driver_override fields as "const char *", just like SPI
   and VDPA. (Mark)
2. Move "count" check to the new helper and add "count" argument. (Michael)
3. Fix typos in docs, patch subject. Extend doc. (Michael, Bjorn)
4. Compare pointers to reduce number of string readings in the helper.
5. Fix clk-imx return value.

Changes since latest v1 (not the old 2019 solution):
====================================================
https://lore.kernel.org/all/708eabb1-7b35-d525-d4c3-451d4a3de84f@rasmusvillemoes.dk/
1. Add helper for setting driver_override.
2. Use the helper.

Dependencies, merging and stable
================================
1. All patches, including last three fixes, depend on the first patch
   introducing the helper.
2. Merging idea: everything via driver core (Greg KH?).
2. The last three commits - fixes - are probably not backportable
   directly, because of this dependency. I don't know how to express
   this dependency here, since stable-kernel-rules.rst mentions only commits as
   possible dependencies.

[1] https://lore.kernel.org/all/1550484960-2392-3-git-send-email-krzk@kernel.org/

Best regards,
Krzysztof

Krzysztof Kozlowski (11):
  driver: platform: Add helper for safer setting of driver_override
  amba: Use driver_set_override() instead of open-coding
  fsl-mc: Use driver_set_override() instead of open-coding
  hv: Use driver_set_override() instead of open-coding
  PCI: Use driver_set_override() instead of open-coding
  s390/cio: Use driver_set_override() instead of open-coding
  spi: Use helper for safer setting of driver_override
  vdpa: Use helper for safer setting of driver_override
  clk: imx: scu: Fix kfree() of static memory on setting driver_override
  slimbus: qcom-ngd: Fix kfree() of static memory on setting
    driver_override
  rpmsg: Fix kfree() of static memory on setting driver_override

 drivers/amba/bus.c              | 28 +++--------------
 drivers/base/driver.c           | 56 +++++++++++++++++++++++++++++++++
 drivers/base/platform.c         | 28 +++--------------
 drivers/bus/fsl-mc/fsl-mc-bus.c | 25 +++------------
 drivers/clk/imx/clk-scu.c       |  7 ++++-
 drivers/hv/vmbus_drv.c          | 28 +++--------------
 drivers/pci/pci-sysfs.c         | 28 +++--------------
 drivers/rpmsg/rpmsg_core.c      |  3 +-
 drivers/rpmsg/rpmsg_internal.h  | 13 ++++++--
 drivers/rpmsg/rpmsg_ns.c        | 14 +++++++--
 drivers/s390/cio/cio.h          |  6 +++-
 drivers/s390/cio/css.c          | 28 +++--------------
 drivers/slimbus/qcom-ngd-ctrl.c | 13 +++++++-
 drivers/spi/spi.c               | 26 +++------------
 drivers/vdpa/vdpa.c             | 29 +++--------------
 include/linux/amba/bus.h        |  6 +++-
 include/linux/device/driver.h   |  2 ++
 include/linux/fsl/mc.h          |  6 ++--
 include/linux/hyperv.h          |  6 +++-
 include/linux/pci.h             |  6 +++-
 include/linux/platform_device.h |  6 +++-
 include/linux/rpmsg.h           |  6 ++--
 include/linux/spi/spi.h         |  2 ++
 include/linux/vdpa.h            |  4 ++-
 24 files changed, 171 insertions(+), 205 deletions(-)

-- 
2.32.0


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[PATCH v4 01/11] driver: platform: Add helper for safer setting of driver_override

[Krzysztof Kozlowski]

Several core drivers and buses expect that driver_override is a
dynamically allocated memory thus later they can kfree() it.

However such assumption is not documented, there were in the past and
there are already users setting it to a string literal. This leads to
kfree() of static memory during device release (e.g. in error paths or
during unbind):

    kernel BUG at ../mm/slub.c:3960!
    Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
    ...
    (kfree) from [<c058da50>] (platform_device_release+0x88/0xb4)
    (platform_device_release) from [<c0585be0>] (device_release+0x2c/0x90)
    (device_release) from [<c0a69050>] (kobject_put+0xec/0x20c)
    (kobject_put) from [<c0f2f120>] (exynos5_clk_probe+0x154/0x18c)
    (exynos5_clk_probe) from [<c058de70>] (platform_drv_probe+0x6c/0xa4)
    (platform_drv_probe) from [<c058b7ac>] (really_probe+0x280/0x414)
    (really_probe) from [<c058baf4>] (driver_probe_device+0x78/0x1c4)
    (driver_probe_device) from [<c0589854>] (bus_for_each_drv+0x74/0xb8)
    (bus_for_each_drv) from [<c058b48c>] (__device_attach+0xd4/0x16c)
    (__device_attach) from [<c058a638>] (bus_probe_device+0x88/0x90)
    (bus_probe_device) from [<c05871fc>] (device_add+0x3dc/0x62c)
    (device_add) from [<c075ff10>] (of_platform_device_create_pdata+0x94/0xbc)
    (of_platform_device_create_pdata) from [<c07600ec>] (of_platform_bus_create+0x1a8/0x4fc)
    (of_platform_bus_create) from [<c0760150>] (of_platform_bus_create+0x20c/0x4fc)
    (of_platform_bus_create) from [<c07605f0>] (of_platform_populate+0x84/0x118)
    (of_platform_populate) from [<c0f3c964>] (of_platform_default_populate_init+0xa0/0xb8)
    (of_platform_default_populate_init) from [<c01031f8>] (do_one_initcall+0x8c/0x404)
    (do_one_initcall) from [<c0f012c0>] (kernel_init_freeable+0x3d0/0x4d8)
    (kernel_init_freeable) from [<c0a7def0>] (kernel_init+0x8/0x114)
    (kernel_init) from [<c01010b4>] (ret_from_fork+0x14/0x20)

Provide a helper which clearly documents the usage of driver_override.
This will allow later to reuse the helper and reduce amount of
duplicated code.

Convert the platform driver to use new helper and make the
driver_override field const char (it is not modified by the core).

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 drivers/base/driver.c           | 56 +++++++++++++++++++++++++++++++++
 drivers/base/platform.c         | 28 +++--------------
 include/linux/device/driver.h   |  2 ++
 include/linux/platform_device.h |  6 +++-
 4 files changed, 67 insertions(+), 25 deletions(-)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 8c0d33e182fd..ba2510117484 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -30,6 +30,62 @@ static struct device *next_device(struct klist_iter *i)
 	return dev;
 }
 
+/**
+ * driver_set_override() - Helper to set or clear driver override.
+ * @dev: Device to change
+ * @override: Address of string to change (e.g. &device->driver_override);
+ *            The contents will be freed and hold newly allocated override.
+ * @s: NUL terminated string, new driver name to force a match, pass empty
+ *     string to clear it
+ * @len: length of @s
+ *
+ * Helper to set or clear driver override in a device, intended for the cases
+ * when the driver_override field is allocated by driver/bus code.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int driver_set_override(struct device *dev, const char **override,
+			const char *s, size_t len)
+{
+	const char *new, *old;
+	char *cp;
+
+	if (!dev || !override || !s)
+		return -EINVAL;
+
+	/*
+	 * The stored value will be used in sysfs show callback (sysfs_emit()),
+	 * which has a length limit of PAGE_SIZE and adds a trailing newline.
+	 * Thus we can store one character less to avoid truncation during sysfs
+	 * show.
+	 */
+	if (len >= (PAGE_SIZE - 1))
+		return -EINVAL;
+
+	new = kstrndup(s, len, GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	cp = strchr(new, '\n');
+	if (cp)
+		*cp = '\0';
+
+	device_lock(dev);
+	old = *override;
+	if (cp != new) {
+		*override = new;
+	} else {
+		kfree(new);
+		*override = NULL;
+	}
+	device_unlock(dev);
+
+	kfree(old);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(driver_set_override);
+
 /**
  * driver_for_each_device - Iterator for devices bound to a driver.
  * @drv: Driver we're iterating.
diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 8cc272fd5c99..b684157b7f2f 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -1275,31 +1275,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct platform_device *pdev = to_platform_device(dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	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);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(dev, &pdev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/device/driver.h b/include/linux/device/driver.h
index 15e7c5e15d62..700453017e1c 100644
--- a/include/linux/device/driver.h
+++ b/include/linux/device/driver.h
@@ -151,6 +151,8 @@ extern int __must_check driver_create_file(struct device_driver *driver,
 extern void driver_remove_file(struct device_driver *driver,
 			       const struct driver_attribute *attr);
 
+int driver_set_override(struct device *dev, const char **override,
+			const char *s, size_t len);
 extern int __must_check driver_for_each_device(struct device_driver *drv,
 					       struct device *start,
 					       void *data,
diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
index 7c96f169d274..582d83ed9a91 100644
--- a/include/linux/platform_device.h
+++ b/include/linux/platform_device.h
@@ -31,7 +31,11 @@ struct platform_device {
 	struct resource	*resource;
 
 	const struct platform_device_id	*id_entry;
-	char *driver_override; /* Driver name to force a match */
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char *driver_override;
 
 	/* MFD cell pointer */
 	struct mfd_cell *mfd_cell;
-- 
2.32.0


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[PATCH v4 02/11] amba: Use driver_set_override() instead of open-coding

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.
Make the driver_override field const char, because it is not modified by
the core and it matches other subsystems.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 drivers/amba/bus.c       | 28 ++++------------------------
 include/linux/amba/bus.h |  6 +++++-
 2 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index d3bd14aaabf6..f3d26d698b77 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -94,31 +94,11 @@ static ssize_t driver_override_store(struct device *_dev,
 				     const char *buf, size_t count)
 {
 	struct amba_device *dev = to_amba_device(_dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	device_lock(_dev);
-	old = dev->driver_override;
-	if (strlen(driver_override)) {
-		dev->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		dev->driver_override = NULL;
-	}
-	device_unlock(_dev);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(_dev, &dev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index 6562f543c3e0..93799a72ff82 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -70,7 +70,11 @@ struct amba_device {
 	unsigned int		cid;
 	struct amba_cs_uci_id	uci;
 	unsigned int		irq[AMBA_NR_IRQS];
-	char			*driver_override;
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char		*driver_override;
 };
 
 struct amba_driver {
-- 
2.32.0


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[PATCH v4 03/11] fsl-mc: Use driver_set_override() instead of open-coding

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.
Make the driver_override field const char, because it is not modified by
the core and it matches other subsystems.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 drivers/bus/fsl-mc/fsl-mc-bus.c | 25 ++++---------------------
 include/linux/fsl/mc.h          |  6 ++++--
 2 files changed, 8 insertions(+), 23 deletions(-)

diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
index 8fd4a356a86e..ba01c7f4de92 100644
--- a/drivers/bus/fsl-mc/fsl-mc-bus.c
+++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
@@ -166,31 +166,14 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
-	char *driver_override, *old = mc_dev->driver_override;
-	char *cp;
+	int ret;
 
 	if (WARN_ON(dev->bus != &fsl_mc_bus_type))
 		return -EINVAL;
 
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	if (strlen(driver_override)) {
-		mc_dev->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		mc_dev->driver_override = NULL;
-	}
-
-	kfree(old);
+	ret = driver_set_override(dev, &mc_dev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/fsl/mc.h b/include/linux/fsl/mc.h
index 7b6c42bfb660..7a87ab9eba99 100644
--- a/include/linux/fsl/mc.h
+++ b/include/linux/fsl/mc.h
@@ -170,7 +170,9 @@ struct fsl_mc_obj_desc {
  * @regions: pointer to array of MMIO region entries
  * @irqs: pointer to array of pointers to interrupts allocated to this device
  * @resource: generic resource associated with this MC object device, if any.
- * @driver_override: driver name to force a match
+ * @driver_override: driver name to force a match; do not set directly,
+ *                   because core frees it; use driver_set_override() to
+ *                   set or clear it.
  *
  * Generic device object for MC object devices that are "attached" to a
  * MC bus.
@@ -204,7 +206,7 @@ struct fsl_mc_device {
 	struct fsl_mc_device_irq **irqs;
 	struct fsl_mc_resource *resource;
 	struct device_link *consumer_link;
-	char   *driver_override;
+	const char *driver_override;
 };
 
 #define to_fsl_mc_device(_dev) \
-- 
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[PATCH v4 04/11] hv: Use driver_set_override() instead of open-coding

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.
Make the driver_override field const char, because it is not modified by
the core and it matches other subsystems.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
---
 drivers/hv/vmbus_drv.c | 28 ++++------------------------
 include/linux/hyperv.h |  6 +++++-
 2 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 60ee8b329f9e..66213ce5579d 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -575,31 +575,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct hv_device *hv_dev = device_to_hv_device(dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	device_lock(dev);
-	old = hv_dev->driver_override;
-	if (strlen(driver_override)) {
-		hv_dev->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		hv_dev->driver_override = NULL;
-	}
-	device_unlock(dev);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(dev, &hv_dev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index fe2e0179ed51..12e2336b23b7 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1257,7 +1257,11 @@ struct hv_device {
 	u16 device_id;
 
 	struct device device;
-	char *driver_override; /* Driver name to force a match */
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char *driver_override;
 
 	struct vmbus_channel *channel;
 	struct kset	     *channels_kset;
-- 
2.32.0


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[PATCH v4 05/11] PCI: Use driver_set_override() instead of open-coding

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.
Make the driver_override field const char, because it is not modified by
the core and it matches other subsystems.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/pci-sysfs.c | 28 ++++------------------------
 include/linux/pci.h     |  6 +++++-
 2 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 602f0fb0b007..5c42965c32c2 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -567,31 +567,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	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);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(dev, &pdev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 60d423d8f0c4..415491fb85f4 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -516,7 +516,11 @@ struct pci_dev {
 	u16		acs_cap;	/* ACS Capability offset */
 	phys_addr_t	rom;		/* Physical address if not from BAR */
 	size_t		romlen;		/* Length if not from BAR */
-	char		*driver_override; /* Driver name to force a match */
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char	*driver_override;
 
 	unsigned long	priv_flags;	/* Private flags for the PCI driver */
 
-- 
2.32.0


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[PATCH v4 06/11] s390/cio: Use driver_set_override() instead of open-coding

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.
Make the driver_override field const char, because it is not modified by
the core and it matches other subsystems.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Vineeth Vijayan <vneethv@linux.ibm.com>
---
 drivers/s390/cio/cio.h |  6 +++++-
 drivers/s390/cio/css.c | 28 ++++------------------------
 2 files changed, 9 insertions(+), 25 deletions(-)

diff --git a/drivers/s390/cio/cio.h b/drivers/s390/cio/cio.h
index 1cb9daf9c645..fa8df50bb49e 100644
--- a/drivers/s390/cio/cio.h
+++ b/drivers/s390/cio/cio.h
@@ -103,7 +103,11 @@ struct subchannel {
 	struct work_struct todo_work;
 	struct schib_config config;
 	u64 dma_mask;
-	char *driver_override; /* Driver name to force a match */
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char *driver_override;
 } __attribute__ ((aligned(8)));
 
 DECLARE_PER_CPU_ALIGNED(struct irb, cio_irb);
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index fa8293335077..913b6ddd040b 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -338,31 +338,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct subchannel *sch = to_subchannel(dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	device_lock(dev);
-	old = sch->driver_override;
-	if (strlen(driver_override)) {
-		sch->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		sch->driver_override = NULL;
-	}
-	device_unlock(dev);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(dev, &sch->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
-- 
2.32.0


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[PATCH v4 07/11] spi: Use helper for safer setting of driver_override

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
---
 drivers/spi/spi.c       | 26 ++++----------------------
 include/linux/spi/spi.h |  2 ++
 2 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6937cf2d59e0..34f311224c47 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -71,29 +71,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct spi_device *spi = to_spi_device(dev);
-	const char *end = memchr(buf, '\n', count);
-	const size_t len = end ? end - buf : count;
-	const char *driver_override, *old;
-
-	/* We need to keep extra room for a newline when displaying value */
-	if (len >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, len, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
+	int ret;
 
-	device_lock(dev);
-	old = spi->driver_override;
-	if (len) {
-		spi->driver_override = driver_override;
-	} else {
-		/* Empty string, disable driver override */
-		spi->driver_override = NULL;
-		kfree(driver_override);
-	}
-	device_unlock(dev);
-	kfree(old);
+	ret = driver_set_override(dev, &spi->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 5f8c063ddff4..f0177f9b6e13 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -138,6 +138,8 @@ extern int spi_delay_exec(struct spi_delay *_delay, struct spi_transfer *xfer);
  *	for driver coldplugging, and in uevents used for hotplugging
  * @driver_override: If the name of a driver is written to this attribute, then
  *	the device will bind to the named driver and only the named driver.
+ *	Do not set directly, because core frees it; use driver_set_override() to
+ *	set or clear it.
  * @cs_gpiod: gpio descriptor of the chipselect line (optional, NULL when
  *	not using a GPIO line)
  * @word_delay: delay to be inserted between consecutive
-- 
2.32.0


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[PATCH v4 08/11] vdpa: Use helper for safer setting of driver_override

[Krzysztof Kozlowski]

Use a helper to set driver_override to reduce amount of duplicated code.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 drivers/vdpa/vdpa.c  | 29 ++++-------------------------
 include/linux/vdpa.h |  4 +++-
 2 files changed, 7 insertions(+), 26 deletions(-)

diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
index 1ea525433a5c..2dabed1df35c 100644
--- a/drivers/vdpa/vdpa.c
+++ b/drivers/vdpa/vdpa.c
@@ -77,32 +77,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct vdpa_device *vdev = dev_to_vdpa(dev);
-	const char *driver_override, *old;
-	char *cp;
+	int ret;
 
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	device_lock(dev);
-	old = vdev->driver_override;
-	if (strlen(driver_override)) {
-		vdev->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		vdev->driver_override = NULL;
-	}
-	device_unlock(dev);
-
-	kfree(old);
+	ret = driver_set_override(dev, &vdev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }
diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
index 721089bb4c84..37117404660e 100644
--- a/include/linux/vdpa.h
+++ b/include/linux/vdpa.h
@@ -64,7 +64,9 @@ struct vdpa_mgmt_dev;
  * struct vdpa_device - representation of a vDPA device
  * @dev: underlying device
  * @dma_dev: the actual device that is performing DMA
- * @driver_override: driver name to force a match
+ * @driver_override: driver name to force a match; do not set directly,
+ *                   because core frees it; use driver_set_override() to
+ *                   set or clear it.
  * @config: the configuration ops for this device.
  * @cf_mutex: Protects get and set access to configuration layout.
  * @index: device index
-- 
2.32.0


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[PATCH v4 09/11] clk: imx: scu: Fix kfree() of static memory on setting driver_override

[Krzysztof Kozlowski]

The driver_override field from platform driver should not be initialized
from static memory (string literal) because the core later kfree() it,
for example when driver_override is set via sysfs.

Use dedicated helper to set driver_override properly.

Fixes: 77d8f3068c63 ("clk: imx: scu: add two cells binding support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 drivers/clk/imx/clk-scu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/imx/clk-scu.c b/drivers/clk/imx/clk-scu.c
index 083da31dc3ea..4b2268b7d0d0 100644
--- a/drivers/clk/imx/clk-scu.c
+++ b/drivers/clk/imx/clk-scu.c
@@ -683,7 +683,12 @@ struct clk_hw *imx_clk_scu_alloc_dev(const char *name,
 		return ERR_PTR(ret);
 	}
 
-	pdev->driver_override = "imx-scu-clk";
+	ret = driver_set_override(&pdev->dev, &pdev->driver_override,
+				  "imx-scu-clk", strlen("imx-scu-clk"));
+	if (ret) {
+		platform_device_put(pdev);
+		return ERR_PTR(ret);
+	}
 
 	ret = imx_clk_scu_attach_pd(&pdev->dev, rsrc_id);
 	if (ret)
-- 
2.32.0


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[PATCH v4 10/11] slimbus: qcom-ngd: Fix kfree() of static memory on setting driver_override

[Krzysztof Kozlowski]

The driver_override field from platform driver should not be initialized
from static memory (string literal) because the core later kfree() it,
for example when driver_override is set via sysfs.

Use dedicated helper to set driver_override properly.

Fixes: 917809e2280b ("slimbus: ngd: Add qcom SLIMBus NGD driver")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---
 drivers/slimbus/qcom-ngd-ctrl.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/slimbus/qcom-ngd-ctrl.c b/drivers/slimbus/qcom-ngd-ctrl.c
index 7040293c2ee8..e5d9fdb81eb0 100644
--- a/drivers/slimbus/qcom-ngd-ctrl.c
+++ b/drivers/slimbus/qcom-ngd-ctrl.c
@@ -1434,6 +1434,7 @@ static int of_qcom_slim_ngd_register(struct device *parent,
 	const struct of_device_id *match;
 	struct device_node *node;
 	u32 id;
+	int ret;
 
 	match = of_match_node(qcom_slim_ngd_dt_match, parent->of_node);
 	data = match->data;
@@ -1455,7 +1456,17 @@ static int of_qcom_slim_ngd_register(struct device *parent,
 		}
 		ngd->id = id;
 		ngd->pdev->dev.parent = parent;
-		ngd->pdev->driver_override = QCOM_SLIM_NGD_DRV_NAME;
+
+		ret = driver_set_override(&ngd->pdev->dev,
+					  &ngd->pdev->driver_override,
+					  QCOM_SLIM_NGD_DRV_NAME,
+					  strlen(QCOM_SLIM_NGD_DRV_NAME));
+		if (ret) {
+			platform_device_put(ngd->pdev);
+			kfree(ngd);
+			of_node_put(node);
+			return ret;
+		}
 		ngd->pdev->dev.of_node = node;
 		ctrl->ngd = ngd;
 
-- 
2.32.0


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[PATCH v4 11/11] rpmsg: Fix kfree() of static memory on setting driver_override

[Krzysztof Kozlowski]

The driver_override field from platform driver should not be initialized
from static memory (string literal) because the core later kfree() it,
for example when driver_override is set via sysfs.

Use dedicated helper to set driver_override properly.

Fixes: 950a7388f02b ("rpmsg: Turn name service into a stand alone driver")
Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
---
 drivers/rpmsg/rpmsg_core.c     |  3 ++-
 drivers/rpmsg/rpmsg_internal.h | 13 +++++++++++--
 drivers/rpmsg/rpmsg_ns.c       | 14 ++++++++++++--
 include/linux/rpmsg.h          |  6 ++++--
 4 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
index d9e612f4f0f2..6e2bf2742973 100644
--- a/drivers/rpmsg/rpmsg_core.c
+++ b/drivers/rpmsg/rpmsg_core.c
@@ -397,7 +397,8 @@ field##_store(struct device *dev, struct device_attribute *attr,	\
 	      const char *buf, size_t sz)				\
 {									\
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);		\
-	char *new, *old;						\
+	const char *old;						\
+	char *new;							\
 									\
 	new = kstrndup(buf, sz, GFP_KERNEL);				\
 	if (!new)							\
diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
index b1245d3ed7c6..31345d6e9a7e 100644
--- a/drivers/rpmsg/rpmsg_internal.h
+++ b/drivers/rpmsg/rpmsg_internal.h
@@ -92,10 +92,19 @@ int rpmsg_release_channel(struct rpmsg_device *rpdev,
  */
 static inline int rpmsg_chrdev_register_device(struct rpmsg_device *rpdev)
 {
+	int ret;
+
 	strcpy(rpdev->id.name, "rpmsg_chrdev");
-	rpdev->driver_override = "rpmsg_chrdev";
+	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
+				  "rpmsg_chrdev", strlen("rpmsg_chrdev"));
+	if (ret)
+		return ret;
+
+	ret = rpmsg_register_device(rpdev);
+	if (ret)
+		kfree(rpdev->driver_override);
 
-	return rpmsg_register_device(rpdev);
+	return ret;
 }
 
 #endif
diff --git a/drivers/rpmsg/rpmsg_ns.c b/drivers/rpmsg/rpmsg_ns.c
index 762ff1ae279f..95a51543f5ad 100644
--- a/drivers/rpmsg/rpmsg_ns.c
+++ b/drivers/rpmsg/rpmsg_ns.c
@@ -20,12 +20,22 @@
  */
 int rpmsg_ns_register_device(struct rpmsg_device *rpdev)
 {
+	int ret;
+
 	strcpy(rpdev->id.name, "rpmsg_ns");
-	rpdev->driver_override = "rpmsg_ns";
+	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
+				  "rpmsg_ns", strlen("rpmsg_ns"));
+	if (ret)
+		return ret;
+
 	rpdev->src = RPMSG_NS_ADDR;
 	rpdev->dst = RPMSG_NS_ADDR;
 
-	return rpmsg_register_device(rpdev);
+	ret = rpmsg_register_device(rpdev);
+	if (ret)
+		kfree(rpdev->driver_override);
+
+	return ret;
 }
 EXPORT_SYMBOL(rpmsg_ns_register_device);
 
diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
index 02fa9116cd60..20c8cd1cde21 100644
--- a/include/linux/rpmsg.h
+++ b/include/linux/rpmsg.h
@@ -41,7 +41,9 @@ struct rpmsg_channel_info {
  * rpmsg_device - device that belong to the rpmsg bus
  * @dev: the device struct
  * @id: device id (used to match between rpmsg drivers and devices)
- * @driver_override: driver name to force a match
+ * @driver_override: driver name to force a match; do not set directly,
+ *                   because core frees it; use driver_set_override() to
+ *                   set or clear it.
  * @src: local address
  * @dst: destination address
  * @ept: the rpmsg endpoint of this channel
@@ -51,7 +53,7 @@ struct rpmsg_channel_info {
 struct rpmsg_device {
 	struct device dev;
 	struct rpmsg_device_id id;
-	char *driver_override;
+	const char *driver_override;
 	u32 src;
 	u32 dst;
 	struct rpmsg_endpoint *ept;
-- 
2.32.0


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Re: [PATCH v4 08/11] vdpa: Use helper for safer setting of driver_override

[Michael S. Tsirkin]

On Sat, Mar 12, 2022 at 02:28:53PM +0100, Krzysztof Kozlowski wrote:
> Use a helper to set driver_override to reduce amount of duplicated code.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/vdpa/vdpa.c  | 29 ++++-------------------------
>  include/linux/vdpa.h |  4 +++-
>  2 files changed, 7 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index 1ea525433a5c..2dabed1df35c 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -77,32 +77,11 @@ static ssize_t driver_override_store(struct device *dev,
>  				     const char *buf, size_t count)
>  {
>  	struct vdpa_device *vdev = dev_to_vdpa(dev);
> -	const char *driver_override, *old;
> -	char *cp;
> +	int ret;
>  
> -	/* We need to keep extra room for a newline */
> -	if (count >= (PAGE_SIZE - 1))
> -		return -EINVAL;
> -
> -	driver_override = kstrndup(buf, count, GFP_KERNEL);
> -	if (!driver_override)
> -		return -ENOMEM;
> -
> -	cp = strchr(driver_override, '\n');
> -	if (cp)
> -		*cp = '\0';
> -
> -	device_lock(dev);
> -	old = vdev->driver_override;
> -	if (strlen(driver_override)) {
> -		vdev->driver_override = driver_override;
> -	} else {
> -		kfree(driver_override);
> -		vdev->driver_override = NULL;
> -	}
> -	device_unlock(dev);
> -
> -	kfree(old);
> +	ret = driver_set_override(dev, &vdev->driver_override, buf, count);
> +	if (ret)
> +		return ret;
>  
>  	return count;
>  }
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index 721089bb4c84..37117404660e 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -64,7 +64,9 @@ struct vdpa_mgmt_dev;
>   * struct vdpa_device - representation of a vDPA device
>   * @dev: underlying device
>   * @dma_dev: the actual device that is performing DMA
> - * @driver_override: driver name to force a match
> + * @driver_override: driver name to force a match; do not set directly,
> + *                   because core frees it; use driver_set_override() to
> + *                   set or clear it.
>   * @config: the configuration ops for this device.
>   * @cf_mutex: Protects get and set access to configuration layout.
>   * @index: device index
> -- 
> 2.32.0


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Re: [PATCH v4 11/11] rpmsg: Fix kfree() of static memory on setting driver_override

[Bjorn Andersson]

On Sat 12 Mar 07:28 CST 2022, Krzysztof Kozlowski wrote:

> The driver_override field from platform driver should not be initialized
> from static memory (string literal) because the core later kfree() it,
> for example when driver_override is set via sysfs.
> 
> Use dedicated helper to set driver_override properly.
> 
> Fixes: 950a7388f02b ("rpmsg: Turn name service into a stand alone driver")
> Fixes: c0cdc19f84a4 ("rpmsg: Driver for user space endpoint interface")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Regards,
Bjorn

> ---
>  drivers/rpmsg/rpmsg_core.c     |  3 ++-
>  drivers/rpmsg/rpmsg_internal.h | 13 +++++++++++--
>  drivers/rpmsg/rpmsg_ns.c       | 14 ++++++++++++--
>  include/linux/rpmsg.h          |  6 ++++--
>  4 files changed, 29 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> index d9e612f4f0f2..6e2bf2742973 100644
> --- a/drivers/rpmsg/rpmsg_core.c
> +++ b/drivers/rpmsg/rpmsg_core.c
> @@ -397,7 +397,8 @@ field##_store(struct device *dev, struct device_attribute *attr,	\
>  	      const char *buf, size_t sz)				\
>  {									\
>  	struct rpmsg_device *rpdev = to_rpmsg_device(dev);		\
> -	char *new, *old;						\
> +	const char *old;						\
> +	char *new;							\
>  									\
>  	new = kstrndup(buf, sz, GFP_KERNEL);				\
>  	if (!new)							\
> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
> index b1245d3ed7c6..31345d6e9a7e 100644
> --- a/drivers/rpmsg/rpmsg_internal.h
> +++ b/drivers/rpmsg/rpmsg_internal.h
> @@ -92,10 +92,19 @@ int rpmsg_release_channel(struct rpmsg_device *rpdev,
>   */
>  static inline int rpmsg_chrdev_register_device(struct rpmsg_device *rpdev)
>  {
> +	int ret;
> +
>  	strcpy(rpdev->id.name, "rpmsg_chrdev");
> -	rpdev->driver_override = "rpmsg_chrdev";
> +	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
> +				  "rpmsg_chrdev", strlen("rpmsg_chrdev"));
> +	if (ret)
> +		return ret;
> +
> +	ret = rpmsg_register_device(rpdev);
> +	if (ret)
> +		kfree(rpdev->driver_override);
>  
> -	return rpmsg_register_device(rpdev);
> +	return ret;
>  }
>  
>  #endif
> diff --git a/drivers/rpmsg/rpmsg_ns.c b/drivers/rpmsg/rpmsg_ns.c
> index 762ff1ae279f..95a51543f5ad 100644
> --- a/drivers/rpmsg/rpmsg_ns.c
> +++ b/drivers/rpmsg/rpmsg_ns.c
> @@ -20,12 +20,22 @@
>   */
>  int rpmsg_ns_register_device(struct rpmsg_device *rpdev)
>  {
> +	int ret;
> +
>  	strcpy(rpdev->id.name, "rpmsg_ns");
> -	rpdev->driver_override = "rpmsg_ns";
> +	ret = driver_set_override(&rpdev->dev, &rpdev->driver_override,
> +				  "rpmsg_ns", strlen("rpmsg_ns"));
> +	if (ret)
> +		return ret;
> +
>  	rpdev->src = RPMSG_NS_ADDR;
>  	rpdev->dst = RPMSG_NS_ADDR;
>  
> -	return rpmsg_register_device(rpdev);
> +	ret = rpmsg_register_device(rpdev);
> +	if (ret)
> +		kfree(rpdev->driver_override);
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(rpmsg_ns_register_device);
>  
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 02fa9116cd60..20c8cd1cde21 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -41,7 +41,9 @@ struct rpmsg_channel_info {
>   * rpmsg_device - device that belong to the rpmsg bus
>   * @dev: the device struct
>   * @id: device id (used to match between rpmsg drivers and devices)
> - * @driver_override: driver name to force a match
> + * @driver_override: driver name to force a match; do not set directly,
> + *                   because core frees it; use driver_set_override() to
> + *                   set or clear it.
>   * @src: local address
>   * @dst: destination address
>   * @ept: the rpmsg endpoint of this channel
> @@ -51,7 +53,7 @@ struct rpmsg_channel_info {
>  struct rpmsg_device {
>  	struct device dev;
>  	struct rpmsg_device_id id;
> -	char *driver_override;
> +	const char *driver_override;
>  	u32 src;
>  	u32 dst;
>  	struct rpmsg_endpoint *ept;
> -- 
> 2.32.0
> 

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Re: [PATCH v4 01/11] driver: platform: Add helper for safer setting of driver_override

[Andy Shevchenko]

On Sat, Mar 12, 2022 at 5:16 PM Krzysztof Kozlowski
<krzysztof.kozlowski@canonical.com> wrote:
>
> Several core drivers and buses expect that driver_override is a
> dynamically allocated memory thus later they can kfree() it.
>
> However such assumption is not documented, there were in the past and
> there are already users setting it to a string literal. This leads to
> kfree() of static memory during device release (e.g. in error paths or
> during unbind):
>
>     kernel BUG at ../mm/slub.c:3960!
>     Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
>     ...
>     (kfree) from [<c058da50>] (platform_device_release+0x88/0xb4)
>     (platform_device_release) from [<c0585be0>] (device_release+0x2c/0x90)
>     (device_release) from [<c0a69050>] (kobject_put+0xec/0x20c)
>     (kobject_put) from [<c0f2f120>] (exynos5_clk_probe+0x154/0x18c)
>     (exynos5_clk_probe) from [<c058de70>] (platform_drv_probe+0x6c/0xa4)
>     (platform_drv_probe) from [<c058b7ac>] (really_probe+0x280/0x414)
>     (really_probe) from [<c058baf4>] (driver_probe_device+0x78/0x1c4)
>     (driver_probe_device) from [<c0589854>] (bus_for_each_drv+0x74/0xb8)
>     (bus_for_each_drv) from [<c058b48c>] (__device_attach+0xd4/0x16c)
>     (__device_attach) from [<c058a638>] (bus_probe_device+0x88/0x90)
>     (bus_probe_device) from [<c05871fc>] (device_add+0x3dc/0x62c)
>     (device_add) from [<c075ff10>] (of_platform_device_create_pdata+0x94/0xbc)
>     (of_platform_device_create_pdata) from [<c07600ec>] (of_platform_bus_create+0x1a8/0x4fc)
>     (of_platform_bus_create) from [<c0760150>] (of_platform_bus_create+0x20c/0x4fc)
>     (of_platform_bus_create) from [<c07605f0>] (of_platform_populate+0x84/0x118)
>     (of_platform_populate) from [<c0f3c964>] (of_platform_default_populate_init+0xa0/0xb8)
>     (of_platform_default_populate_init) from [<c01031f8>] (do_one_initcall+0x8c/0x404)

>     (do_one_initcall) from [<c0f012c0>] (kernel_init_freeable+0x3d0/0x4d8)
>     (kernel_init_freeable) from [<c0a7def0>] (kernel_init+0x8/0x114)
>     (kernel_init) from [<c01010b4>] (ret_from_fork+0x14/0x20)

I believe you may remove these three.

> Provide a helper which clearly documents the usage of driver_override.
> This will allow later to reuse the helper and reduce amount of

the amount

> duplicated code.

> Convert the platform driver to use new helper and make the

a new

> driver_override field const char (it is not modified by the core).

...

> +/**
> + * driver_set_override() - Helper to set or clear driver override.
> + * @dev: Device to change
> + * @override: Address of string to change (e.g. &device->driver_override);
> + *            The contents will be freed and hold newly allocated override.
> + * @s: NUL terminated string, new driver name to force a match, pass empty

NUL-terminated? (44 vs 115 occurrences)

> + *     string to clear it
> + * @len: length of @s
> + *
> + * Helper to set or clear driver override in a device, intended for the cases
> + * when the driver_override field is allocated by driver/bus code.
> + *
> + * Returns: 0 on success or a negative error code on failure.
> + */
> +int driver_set_override(struct device *dev, const char **override,
> +                       const char *s, size_t len)
> +{
> +       const char *new, *old;
> +       char *cp;
> +
> +       if (!dev || !override || !s)
> +               return -EINVAL;
> +
> +       /*
> +        * The stored value will be used in sysfs show callback (sysfs_emit()),
> +        * which has a length limit of PAGE_SIZE and adds a trailing newline.
> +        * Thus we can store one character less to avoid truncation during sysfs
> +        * show.
> +        */
> +       if (len >= (PAGE_SIZE - 1))
> +               return -EINVAL;
> +
> +       new = kstrndup(s, len, GFP_KERNEL);
> +       if (!new)
> +               return -ENOMEM;
> +
> +       cp = strchr(new, '\n');
> +       if (cp)
> +               *cp = '\0';

AFAIU you may reduce memory footprint by

cp = strnchr(new, len, '\n');
if (cp)
  len = s - cp;

new = kstrndup(...);

> +       device_lock(dev);
> +       old = *override;
> +       if (cp != new) {
> +               *override = new;
> +       } else {
> +               kfree(new);
> +               *override = NULL;
> +       }
> +       device_unlock(dev);
> +
> +       kfree(old);
> +
> +       return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko

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Re: [PATCH v4 05/11] PCI: Use driver_set_override() instead of open-coding

[Andy Shevchenko]

On Sat, Mar 12, 2022 at 4:09 PM Krzysztof Kozlowski
<krzysztof.kozlowski@canonical.com> wrote:
>
> Use a helper to set driver_override to reduce amount of duplicated code.

the amount

> Make the driver_override field const char, because it is not modified by
> the core and it matches other subsystems.


Seems like mine #4 here
https://gist.github.com/andy-shev/a2cb1ee4767d6d2f5d20db53ecb9aabc :-)
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Thanks!

> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>  drivers/pci/pci-sysfs.c | 28 ++++------------------------
>  include/linux/pci.h     |  6 +++++-
>  2 files changed, 9 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 602f0fb0b007..5c42965c32c2 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -567,31 +567,11 @@ static ssize_t driver_override_store(struct device *dev,
>                                      const char *buf, size_t count)
>  {
>         struct pci_dev *pdev = to_pci_dev(dev);
> -       char *driver_override, *old, *cp;
> -
> -       /* We need to keep extra room for a newline */
> -       if (count >= (PAGE_SIZE - 1))
> -               return -EINVAL;
> -
> -       driver_override = kstrndup(buf, count, GFP_KERNEL);
> -       if (!driver_override)
> -               return -ENOMEM;
> -
> -       cp = strchr(driver_override, '\n');
> -       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);
> +       int ret;
>
> -       kfree(old);
> +       ret = driver_set_override(dev, &pdev->driver_override, buf, count);
> +       if (ret)
> +               return ret;
>
>         return count;
>  }
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 60d423d8f0c4..415491fb85f4 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -516,7 +516,11 @@ struct pci_dev {
>         u16             acs_cap;        /* ACS Capability offset */
>         phys_addr_t     rom;            /* Physical address if not from BAR */
>         size_t          romlen;         /* Length if not from BAR */
> -       char            *driver_override; /* Driver name to force a match */
> +       /*
> +        * Driver name to force a match.  Do not set directly, because core
> +        * frees it.  Use driver_set_override() to set or clear it.
> +        */
> +       const char      *driver_override;
>
>         unsigned long   priv_flags;     /* Private flags for the PCI driver */
>
> --
> 2.32.0
>


-- 
With Best Regards,
Andy Shevchenko

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Re: [PATCH v4 08/11] vdpa: Use helper for safer setting of driver_override

[Michael S. Tsirkin]

On Sat, Mar 12, 2022 at 02:28:53PM +0100, Krzysztof Kozlowski wrote:
> Use a helper to set driver_override to reduce amount of duplicated code.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

feel free to merge with the rest of the patchset.

> ---
>  drivers/vdpa/vdpa.c  | 29 ++++-------------------------
>  include/linux/vdpa.h |  4 +++-
>  2 files changed, 7 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index 1ea525433a5c..2dabed1df35c 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -77,32 +77,11 @@ static ssize_t driver_override_store(struct device *dev,
>  				     const char *buf, size_t count)
>  {
>  	struct vdpa_device *vdev = dev_to_vdpa(dev);
> -	const char *driver_override, *old;
> -	char *cp;
> +	int ret;
>  
> -	/* We need to keep extra room for a newline */
> -	if (count >= (PAGE_SIZE - 1))
> -		return -EINVAL;
> -
> -	driver_override = kstrndup(buf, count, GFP_KERNEL);
> -	if (!driver_override)
> -		return -ENOMEM;
> -
> -	cp = strchr(driver_override, '\n');
> -	if (cp)
> -		*cp = '\0';
> -
> -	device_lock(dev);
> -	old = vdev->driver_override;
> -	if (strlen(driver_override)) {
> -		vdev->driver_override = driver_override;
> -	} else {
> -		kfree(driver_override);
> -		vdev->driver_override = NULL;
> -	}
> -	device_unlock(dev);
> -
> -	kfree(old);
> +	ret = driver_set_override(dev, &vdev->driver_override, buf, count);
> +	if (ret)
> +		return ret;
>  
>  	return count;
>  }
> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> index 721089bb4c84..37117404660e 100644
> --- a/include/linux/vdpa.h
> +++ b/include/linux/vdpa.h
> @@ -64,7 +64,9 @@ struct vdpa_mgmt_dev;
>   * struct vdpa_device - representation of a vDPA device
>   * @dev: underlying device
>   * @dma_dev: the actual device that is performing DMA
> - * @driver_override: driver name to force a match
> + * @driver_override: driver name to force a match; do not set directly,
> + *                   because core frees it; use driver_set_override() to
> + *                   set or clear it.
>   * @config: the configuration ops for this device.
>   * @cf_mutex: Protects get and set access to configuration layout.
>   * @index: device index
> -- 
> 2.32.0


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Re: [PATCH v4 01/11] driver: platform: Add helper for safer setting of driver_override

[Krzysztof Kozlowski]

On 15/03/2022 18:59, Andy Shevchenko wrote:
> On Sat, Mar 12, 2022 at 5:16 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@canonical.com> wrote:
>>
>> Several core drivers and buses expect that driver_override is a
>> dynamically allocated memory thus later they can kfree() it.
>>
>> However such assumption is not documented, there were in the past and
>> there are already users setting it to a string literal. This leads to
>> kfree() of static memory during device release (e.g. in error paths or
>> during unbind):
>>
>>     kernel BUG at ../mm/slub.c:3960!
>>     Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
>>     ...
>>     (kfree) from [<c058da50>] (platform_device_release+0x88/0xb4)
>>     (platform_device_release) from [<c0585be0>] (device_release+0x2c/0x90)
>>     (device_release) from [<c0a69050>] (kobject_put+0xec/0x20c)
>>     (kobject_put) from [<c0f2f120>] (exynos5_clk_probe+0x154/0x18c)
>>     (exynos5_clk_probe) from [<c058de70>] (platform_drv_probe+0x6c/0xa4)
>>     (platform_drv_probe) from [<c058b7ac>] (really_probe+0x280/0x414)
>>     (really_probe) from [<c058baf4>] (driver_probe_device+0x78/0x1c4)
>>     (driver_probe_device) from [<c0589854>] (bus_for_each_drv+0x74/0xb8)
>>     (bus_for_each_drv) from [<c058b48c>] (__device_attach+0xd4/0x16c)
>>     (__device_attach) from [<c058a638>] (bus_probe_device+0x88/0x90)
>>     (bus_probe_device) from [<c05871fc>] (device_add+0x3dc/0x62c)
>>     (device_add) from [<c075ff10>] (of_platform_device_create_pdata+0x94/0xbc)
>>     (of_platform_device_create_pdata) from [<c07600ec>] (of_platform_bus_create+0x1a8/0x4fc)
>>     (of_platform_bus_create) from [<c0760150>] (of_platform_bus_create+0x20c/0x4fc)
>>     (of_platform_bus_create) from [<c07605f0>] (of_platform_populate+0x84/0x118)
>>     (of_platform_populate) from [<c0f3c964>] (of_platform_default_populate_init+0xa0/0xb8)
>>     (of_platform_default_populate_init) from [<c01031f8>] (do_one_initcall+0x8c/0x404)
> 
>>     (do_one_initcall) from [<c0f012c0>] (kernel_init_freeable+0x3d0/0x4d8)
>>     (kernel_init_freeable) from [<c0a7def0>] (kernel_init+0x8/0x114)
>>     (kernel_init) from [<c01010b4>] (ret_from_fork+0x14/0x20)
> 
> I believe you may remove these three.

Sure (for this and later comments).

> 
>> Provide a helper which clearly documents the usage of driver_override.
>> This will allow later to reuse the helper and reduce amount of
> 
> the amount
> 
>> duplicated code.
> 
>> Convert the platform driver to use new helper and make the
> 
> a new
> 
>> driver_override field const char (it is not modified by the core).
> 
> ...
> 
>> +/**
>> + * driver_set_override() - Helper to set or clear driver override.
>> + * @dev: Device to change
>> + * @override: Address of string to change (e.g. &device->driver_override);
>> + *            The contents will be freed and hold newly allocated override.
>> + * @s: NUL terminated string, new driver name to force a match, pass empty
> 
> NUL-terminated? (44 vs 115 occurrences)
> 
>> + *     string to clear it
>> + * @len: length of @s
>> + *
>> + * Helper to set or clear driver override in a device, intended for the cases
>> + * when the driver_override field is allocated by driver/bus code.
>> + *
>> + * Returns: 0 on success or a negative error code on failure.
>> + */
>> +int driver_set_override(struct device *dev, const char **override,
>> +                       const char *s, size_t len)
>> +{
>> +       const char *new, *old;
>> +       char *cp;
>> +
>> +       if (!dev || !override || !s)
>> +               return -EINVAL;
>> +
>> +       /*
>> +        * The stored value will be used in sysfs show callback (sysfs_emit()),
>> +        * which has a length limit of PAGE_SIZE and adds a trailing newline.
>> +        * Thus we can store one character less to avoid truncation during sysfs
>> +        * show.
>> +        */
>> +       if (len >= (PAGE_SIZE - 1))
>> +               return -EINVAL;
>> +
>> +       new = kstrndup(s, len, GFP_KERNEL);
>> +       if (!new)
>> +               return -ENOMEM;
>> +
>> +       cp = strchr(new, '\n');
>> +       if (cp)
>> +               *cp = '\0';
> 
> AFAIU you may reduce memory footprint by
> 
> cp = strnchr(new, len, '\n');
> if (cp)
>   len = s - cp;
> 
> new = kstrndup(...);
>

Indeed, thanks.

Best regards,
Krzysztof

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