| Message ID | 20220227135214.145599-2-krzysztof.kozlowski@canonical.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3,01/11] driver: platform: Add helper for safer setting of driver_override | expand |
On 28/02/2022 11:51, Abel Vesa wrote: > On 22-02-27 14:52:04, Krzysztof Kozlowski 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) >> >> 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) > > TBH, I think it would make more sense to have this generic > driver_set_override receive only the dev and the string. And then, > each bus type will have their own implementation that handle things > their own way. This would allow all the drivers that will use this to > do something like this: > > ret = driver_set_override(&pdev->dev, "override_string"); > > I think it would look more cleaner. > The interface in general is not for the drivers. Drivers use it in exceptions (few cases in entire kernel) but many times they actually do not need to. Adding a dedicated driver_set_override() brings intention that such usage is welcomed... but it's not. :) Best regards, Krzysztof
On Sun, Feb 27, 2022 at 02:52:04PM +0100, Krzysztof Kozlowski wrote: > Several core drivers and buses expect that driver_override is a > dynamically allocated memory thus later they can kfree() it. > +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 */ It would help a lot to extend this comment with a hint about where the room for a newline is needed. It was confusing even before, but it's much more so now that the check is in a completely different file than the "show" functions that need the space. > + if (len >= (PAGE_SIZE - 1)) > + return -EINVAL;
On 28/02/2022 21:03, Bjorn Helgaas wrote: > On Sun, Feb 27, 2022 at 02:52:04PM +0100, Krzysztof Kozlowski wrote: >> Several core drivers and buses expect that driver_override is a >> dynamically allocated memory thus later they can kfree() it. > >> +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 */ > > It would help a lot to extend this comment with a hint about where the > room for a newline is needed. It was confusing even before, but it's > much more so now that the check is in a completely different file than > the "show" functions that need the space. > Indeed, this needs explanation. Best regards, Krzysztof
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;
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(-)