| Message ID | 20220419113435.246203-2-krzysztof.kozlowski@linaro.org |
|---|---|
| State | Accepted |
| Commit | 6c2f421174273de8f83cde4286d1c076d43a2d35 |
| Headers | show |
| Series | Fix broken usage of driver_override (and kfree of static memory) | expand |
On Tue, Apr 19, 2022 at 1:34 PM Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> 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) > > Provide a helper which clearly documents the usage of driver_override. > This will allow later to reuse the helper and reduce the amount of > duplicated code. > > Convert the platform driver to use a new helper and make the > driver_override field const char (it is not modified by the core). > > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> > --- > drivers/base/driver.c | 69 +++++++++++++++++++++++++++++++++ > drivers/base/platform.c | 28 ++----------- > include/linux/device/driver.h | 2 + > include/linux/platform_device.h | 6 ++- > 4 files changed, 80 insertions(+), 25 deletions(-) > > diff --git a/drivers/base/driver.c b/drivers/base/driver.c > index 8c0d33e182fd..1b9d47b10bd0 100644 > --- a/drivers/base/driver.c > +++ b/drivers/base/driver.c > @@ -30,6 +30,75 @@ 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. I would stick to one-line description here and possibly expand them in the body of the comment. Regardless, I think that the series is an improvement, so please feel free to add Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> to this patch and Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> to the other patches in the series. > + * @s: NUL-terminated string, new driver name to force a match, pass empty > + * string to clear it ("" or "\n", where the latter is only for sysfs > + * interface). > + * @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 (!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; > + > + if (!len) { > + /* Empty string passed - clear override */ > + device_lock(dev); > + old = *override; > + *override = NULL; > + device_unlock(dev); > + kfree(old); > + > + return 0; > + } > + > + cp = strnchr(s, len, '\n'); > + if (cp) > + len = cp - s; > + > + new = kstrndup(s, len, GFP_KERNEL); > + if (!new) > + return -ENOMEM; > + > + device_lock(dev); > + old = *override; > + if (cp != s) { > + *override = new; > + } else { > + /* "\n" passed - clear override */ > + 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 >
diff --git a/drivers/base/driver.c b/drivers/base/driver.c index 8c0d33e182fd..1b9d47b10bd0 100644 --- a/drivers/base/driver.c +++ b/drivers/base/driver.c @@ -30,6 +30,75 @@ 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 ("" or "\n", where the latter is only for sysfs + * interface). + * @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 (!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; + + if (!len) { + /* Empty string passed - clear override */ + device_lock(dev); + old = *override; + *override = NULL; + device_unlock(dev); + kfree(old); + + return 0; + } + + cp = strnchr(s, len, '\n'); + if (cp) + len = cp - s; + + new = kstrndup(s, len, GFP_KERNEL); + if (!new) + return -ENOMEM; + + device_lock(dev); + old = *override; + if (cp != s) { + *override = new; + } else { + /* "\n" passed - clear override */ + 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;
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) Provide a helper which clearly documents the usage of driver_override. This will allow later to reuse the helper and reduce the amount of duplicated code. Convert the platform driver to use a new helper and make the driver_override field const char (it is not modified by the core). Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> --- drivers/base/driver.c | 69 +++++++++++++++++++++++++++++++++ drivers/base/platform.c | 28 ++----------- include/linux/device/driver.h | 2 + include/linux/platform_device.h | 6 ++- 4 files changed, 80 insertions(+), 25 deletions(-)