Re: [PATCH] driver core: platform: Fix the usage of platform device name(pdev->name)

[Krzysztof Kozlowski]

On Tue, 23 Apr 2019 at 05:36, Venkata Narendra Kumar Gutta
<vnkgutta@xxxxxxxxxxxxxx> wrote:
>
> Platform core is using pdev->name as the platform device name to do
> the binding of the devices with the drivers. But, when the platform
> driver overrides the platform device name with dev_set_name(),
> the pdev->name is pointing to a location which is freed and becomes

If pdev->name is invalid then it should be removed/fixed. Why leaving
it pointing to wrong place and changing the users to something else?
This looks like either duct-tape for real problem.

> an invalid parameter to do the binding match.
>
> use-after-free instance:
>
> [   33.325013] BUG: KASAN: use-after-free in strcmp+0x8c/0xb0
> [   33.330646] Read of size 1 at addr ffffffc10beae600 by task modprobe
> [   33.339068] CPU: 5 PID: 518 Comm: modprobe Tainted:
>                         G S      W  O      4.19.30+ #3
> [   33.346835] Hardware name: MTP (DT)
> [   33.350419] Call trace:
> [   33.352941]  dump_backtrace+0x0/0x3b8
> [   33.356713]  show_stack+0x24/0x30
> [   33.360119]  dump_stack+0x160/0x1d8
> [   33.363709]  print_address_description+0x84/0x2e0
> [   33.368549]  kasan_report+0x26c/0x2d0
> [   33.372322]  __asan_report_load1_noabort+0x2c/0x38
> [   33.377248]  strcmp+0x8c/0xb0
> [   33.380306]  platform_match+0x70/0x1f8
> [   33.384168]  __driver_attach+0x78/0x3a0
> [   33.388111]  bus_for_each_dev+0x13c/0x1b8
> [   33.392237]  driver_attach+0x4c/0x58
> [   33.395910]  bus_add_driver+0x350/0x560
> [   33.399854]  driver_register+0x23c/0x328
> [   33.403886]  __platform_driver_register+0xd0/0xe0
>
> So, use dev_name(&pdev->dev), which fetches the platform device name from
> the kobject(dev->kobj->name) of the device instead of the pdev->name.
>
> Signed-off-by: Venkata Narendra Kumar Gutta <vnkgutta@xxxxxxxxxxxxxx>
> ---
>  drivers/base/platform.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index dab0a5a..0e23aa2 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -888,7 +888,7 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *a,
>         if (len != -ENODEV)
>                 return len;
>
> -       len = snprintf(buf, PAGE_SIZE, "platform:%s\n", pdev->name);
> +       len = snprintf(buf, PAGE_SIZE, "platform:%s\n", dev_name(&pdev->dev));
>
>         return (len >= PAGE_SIZE) ? (PAGE_SIZE - 1) : len;
>  }
> @@ -964,7 +964,7 @@ static int platform_uevent(struct device *dev, struct kobj_uevent_env *env)
>                 return rc;
>
>         add_uevent_var(env, "MODALIAS=%s%s", PLATFORM_MODULE_PREFIX,
> -                       pdev->name);
> +                       dev_name(&pdev->dev));

This is wrong fix and it causes ARM Vexpress board fail to boot under
QEMU (but probably in real world as well). The problem is in not
mached drivers. For example the pdev->name is "vexpress-syscfg" and
dev_name(&pdev->dev) is "vexpress-syscfg.6.auto". The effect - none of
AMBA devices are registered, including missing MMC device (mmci.c,
arm,pl180).

One can see the error of missing root device:
[   13.458982] VFS: Cannot open root device "mmcblk0" or
unknown-block(0,0): error -6

... also before there is a warning like:
[    0.285029] ------------[ cut here ]------------
[    0.285507] WARNING: CPU: 0 PID: 1 at
/home/krzk/dev/yocto-proceq/build/workspace/sources/linux-mainline-next/drivers/bus/vexpress-config.c:183
vexpress_config_init+0x90/0xe0
[    0.285936] Modules linked in:
[    0.286251] CPU: 0 PID: 1 Comm: swapper Tainted: G        W
5.1.0-rc6-next-20190429-g0593ae1f5df5 #27
[    0.286507] Hardware name: ARM-Versatile Express
[    0.286977] [<8010e05c>] (unwind_backtrace) from [<8010b76c>]
(show_stack+0x10/0x14)
[    0.287219] [<8010b76c>] (show_stack) from [<8011ac64>] (__warn+0xf8/0x110)
[    0.287400] [<8011ac64>] (__warn) from [<8011ad94>]
(warn_slowpath_null+0x40/0x48)
[    0.287579] [<8011ad94>] (warn_slowpath_null) from [<809151bc>]
(vexpress_config_init+0x90/0xe0)
[    0.287811] [<809151bc>] (vexpress_config_init) from [<80102710>]
(do_one_initcall+0x54/0x1b4)
[    0.288014] [<80102710>] (do_one_initcall) from [<80900e84>]
(kernel_init_freeable+0x12c/0x1c8)
[    0.288214] [<80900e84>] (kernel_init_freeable) from [<80634048>]
(kernel_init+0x8/0x110)
[    0.288388] [<80634048>] (kernel_init) from [<801010e8>]
(ret_from_fork+0x14/0x2c)
[    0.288597] Exception stack(0x86835fb0 to 0x86835ff8)
[    0.288882] 5fa0:                                     00000000
00000000 00000000 00000000
[    0.289193] 5fc0: 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000
[    0.289479] 5fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[    0.289776] ---[ end trace 3f0995a2bae83983 ]---

Best regards,
Krzysztof