| Message ID | 20220312132856.65163-2-krzysztof.kozlowski@canonical.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Fix broken usage of driver_override (and kfree of static memory) | expand |
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; > +}
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
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;
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(-)