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 | 51 +++++++++++++++++++++++++++++++++ drivers/base/platform.c | 28 +++--------------- include/linux/device/driver.h | 2 ++ include/linux/platform_device.h | 7 ++++- 4 files changed, 63 insertions(+), 25 deletions(-)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c index 8c0d33e182fd..353750b0bbc5 100644 --- a/drivers/base/driver.c +++ b/drivers/base/driver.c @@ -30,6 +30,57 @@ 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; + + /* We need to keep extra room for a newline */ + 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 6cb04ac48bf0..8dd87f44bd74 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..e39963889aa3 100644 --- a/include/linux/platform_device.h +++ b/include/linux/platform_device.h @@ -31,7 +31,12 @@ 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;

Use a helper for seting 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 | 7 ++++++- 2 files changed, 10 insertions(+), 25 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c index e1a5eca3ae3c..9dffa17f50c0 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 6c7f47846971..7c703cb7a3cf 100644 --- a/include/linux/amba/bus.h +++ b/include/linux/amba/bus.h @@ -70,7 +70,12 @@ 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 {

Use a helper for seting 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/hv/vmbus_drv.c | 28 ++++------------------------ include/linux/hyperv.h | 7 ++++++- 2 files changed, 10 insertions(+), 25 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 12a2b37e87f3..a0ff4139c3d2 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..beea11874be2 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -1257,7 +1257,12 @@ 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;

Use a helper for seting 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/pci/pci-sysfs.c | 28 ++++------------------------ include/linux/pci.h | 7 ++++++- 2 files changed, 10 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 8253a5413d7c..5c00a8aebdf9 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -516,7 +516,12 @@ 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 */

Use a helper for seting driver_override to reduce amount of duplicated code.

Signed-off-by: Krzysztof Kozlowski krzysztof.kozlowski@canonical.com --- 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 4599b121d744..9d0b11017741 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -72,29 +72,11 @@ 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 7ab3fed7b804..f99bbb20dd4b 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -136,6 +136,8 @@ 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_gpio: LEGACY: gpio number of the chipselect line (optional, -ENOENT when * not using a GPIO line) use cs_gpiod in new drivers by opting in on * the spi_master.

Use a helper for seting 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 9846c9de4bfa..2d924a89ce28 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 2de442ececae..89ec4e4d4cdc 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