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;+}