Re: Use-after-free with deferred driver probing and __initconst
adding /me
On 12/04/17 04:24, Greg Kroah-Hartman wrote:
> On Sun, Dec 03, 2017 at 07:19:53PM +0200, Dan Aloni wrote:
>> Hi all,
>>
>> [[ CC'ed: folks relating to the original __*_refok family of attributes,
>> deferred probing, Open Firmware maintainer, drivers/base/ maintainer,
>> kernel harderning, LKML ]]
>>
>> It seems that it is possible to cause a use-after-free in the base driver
>> platform code using a set of combined circumstances which I describe below.
>> The instance of the issue happens on a patched 4.4 kernel at a client of
>> mine.
>>
>> [6.173692] Process kworker/u12:3 (pid: 173, stack limit =
>> 0xfc3ea92b8000)
>> [6.180902] Call trace:
>> [6.183345] [] __of_match_node+0x48/0x8c
>> [6.188820] [] of_match_node+0x44/0x68
>> [6.194125] [] of_match_device+0x34/0x48
>> [6.199603] [] platform_match+0x34/0xa8
>> [6.204991] [] __device_attach_driver+0x60/0xc8
>> [6.211077] [] bus_for_each_drv+0x60/0xac
>> [6.216640] [] __device_attach+0x98/0x124
>> [6.03] [] device_initial_probe+0x24/0x30
>> [6.228111] [] bus_probe_device+0x38/0xa0
>> [6.233677] [] deferred_probe_work_func+0x108/0x128
>> [6.240111] [] process_one_work+0x268/0x444
>> [6.245849] [] worker_thread+0x274/0x404
>> [6.251329] [] kthread+0xe0/0xe8
>> [6.256114] [] ret_from_fork+0x10/0x50
>> [6.261415] ---[ end trace fccad0f7d2c2142a ]---
>> [6.271293] note: kworker/u12:3[173] exited with preempt_count 1
>> [6.277342] Unable to handle kernel paging request at virtual address
>> ffd8
>>
>> It happens while booting, and among other things it requires having platform
>> OF drivers marking their `of_driver_id` arrays as `__initconst`, e.g:
>>
>> static const struct of_device_id some_driver_of[] __initconst = {
>> ...
>> {},
>> };
>>
>> Given a platform driver that uses deferred probing, these arrays marked as
>> `__initconst` could be accessed from a deferred probe path after the init
>> section of the kernel has been freed. I have not seen anything in the API
>> related deferred probing that can guard from this scenario.
>>
>> On kernels prior to KASLR the access is not detected, but it can still
>> happen,
>> potentially accessing memory that was returned to the page allocator.
>>
>> On 4.15-rc1, the following shows the ratio between instances of
>> `of_device_id`
>> arrays and the number of them which are declared`__initconst`:
>>
>> $ git grep 'struct of_device_id.*\[\]' | wc -l
>> 3089
>>
>> $ git grep 'struct of_device_id.*\[\]' | grep __initconst | wc -l
>> 117
>>
>> Not all of these instances are platform drivers, but perhaps deferred
>> probing with other types of drivers may cause similar issues.
>>
>> Perhaps it is worthwhile patching stable kernels for the removal of
>> `__initconst` on these arrays?
>
> Yes, if those patches are in Linus's tree, that fixes a bug.
>
>> And for the larger question -
>>
>> Freeing of init sections poses an exploitable vulnerability if that memory
>> is not unmapped, _and_ if there are still accesses taking place due to bugs
>> of this kind. Linux's build process is supposed to detect references from
>> non-freed sections to the freed sections, but clearly this instance has
>> not been detected during build, particularly because we have the `__ref`,
>> `__refdata`, and `__refconst` attributes which suppress those checks.
>>
>> Perhaps as a harderning measure, older kernels should be patched with a
>> config option for not freeing init sections?
>
> Older kernels should just get the fixes that are in newer kernels :)
>
> If you have specific pointers to commits that resolve these issues, I'll
> be glad to queue them up in the stable kernels.
>
> Yes, it is a whack-a-mole fixup, a much better option would be what you
> suggest. Perhaps we need to fix the build to properly mark these
> section references as errors like other ones are?
>
> thanks,
>
> greg k-h
>
Re: Use-after-free with deferred driver probing and __initconst
adding /me
On 12/03/17 12:19, Dan Aloni wrote:
> Hi all,
>
> [[ CC'ed: folks relating to the original __*_refok family of attributes,
> deferred probing, Open Firmware maintainer, drivers/base/ maintainer,
> kernel harderning, LKML ]]
>
> It seems that it is possible to cause a use-after-free in the base driver
> platform code using a set of combined circumstances which I describe below.
> The instance of the issue happens on a patched 4.4 kernel at a client of
> mine.
>
> [6.173692] Process kworker/u12:3 (pid: 173, stack limit =
> 0xfc3ea92b8000)
> [6.180902] Call trace:
> [6.183345] [] __of_match_node+0x48/0x8c
> [6.188820] [] of_match_node+0x44/0x68
> [6.194125] [] of_match_device+0x34/0x48
> [6.199603] [] platform_match+0x34/0xa8
> [6.204991] [] __device_attach_driver+0x60/0xc8
> [6.211077] [] bus_for_each_drv+0x60/0xac
> [6.216640] [] __device_attach+0x98/0x124
> [6.03] [] device_initial_probe+0x24/0x30
> [6.228111] [] bus_probe_device+0x38/0xa0
> [6.233677] [] deferred_probe_work_func+0x108/0x128
> [6.240111] [] process_one_work+0x268/0x444
> [6.245849] [] worker_thread+0x274/0x404
> [6.251329] [] kthread+0xe0/0xe8
> [6.256114] [] ret_from_fork+0x10/0x50
> [6.261415] ---[ end trace fccad0f7d2c2142a ]---
> [6.271293] note: kworker/u12:3[173] exited with preempt_count 1
> [6.277342] Unable to handle kernel paging request at virtual address
> ffd8
>
> It happens while booting, and among other things it requires having platform
> OF drivers marking their `of_driver_id` arrays as `__initconst`, e.g:
>
> static const struct of_device_id some_driver_of[] __initconst = {
> ...
> {},
> };
>
> Given a platform driver that uses deferred probing, these arrays marked as
> `__initconst` could be accessed from a deferred probe path after the init
> section of the kernel has been freed. I have not seen anything in the API
> related deferred probing that can guard from this scenario.
>
> On kernels prior to KASLR the access is not detected, but it can still happen,
> potentially accessing memory that was returned to the page allocator.
>
> On 4.15-rc1, the following shows the ratio between instances of `of_device_id`
> arrays and the number of them which are declared`__initconst`:
>
> $ git grep 'struct of_device_id.*\[\]' | wc -l
> 3089
>
> $ git grep 'struct of_device_id.*\[\]' | grep __initconst | wc -l
> 117
>
> Not all of these instances are platform drivers, but perhaps deferred
> probing with other types of drivers may cause similar issues.
>
> Perhaps it is worthwhile patching stable kernels for the removal of
> `__initconst` on these arrays?
>
>
> And for the larger question -
>
> Freeing of init sections poses an exploitable vulnerability if that memory
> is not unmapped, _and_ if there are still accesses taking place due to bugs
> of this kind. Linux's build process is supposed to detect references from
> non-freed sections to the freed sections, but clearly this instance has
> not been detected during build, particularly because we have the `__ref`,
> `__refdata`, and `__refconst` attributes which suppress those checks.
>
> Perhaps as a harderning measure, older kernels should be patched with a
> config option for not freeing init sections?
>
> --
> Dan Aloni
>
Re: Use-after-free with deferred driver probing and __initconst
On Sun, Dec 03, 2017 at 07:19:53PM +0200, Dan Aloni wrote:
> Hi all,
>
> [[ CC'ed: folks relating to the original __*_refok family of attributes,
> deferred probing, Open Firmware maintainer, drivers/base/ maintainer,
> kernel harderning, LKML ]]
>
> It seems that it is possible to cause a use-after-free in the base driver
> platform code using a set of combined circumstances which I describe below.
> The instance of the issue happens on a patched 4.4 kernel at a client of
> mine.
>
> [6.173692] Process kworker/u12:3 (pid: 173, stack limit =
> 0xfc3ea92b8000)
> [6.180902] Call trace:
> [6.183345] [] __of_match_node+0x48/0x8c
> [6.188820] [] of_match_node+0x44/0x68
> [6.194125] [] of_match_device+0x34/0x48
> [6.199603] [] platform_match+0x34/0xa8
> [6.204991] [] __device_attach_driver+0x60/0xc8
> [6.211077] [] bus_for_each_drv+0x60/0xac
> [6.216640] [] __device_attach+0x98/0x124
> [6.03] [] device_initial_probe+0x24/0x30
> [6.228111] [] bus_probe_device+0x38/0xa0
> [6.233677] [] deferred_probe_work_func+0x108/0x128
> [6.240111] [] process_one_work+0x268/0x444
> [6.245849] [] worker_thread+0x274/0x404
> [6.251329] [] kthread+0xe0/0xe8
> [6.256114] [] ret_from_fork+0x10/0x50
> [6.261415] ---[ end trace fccad0f7d2c2142a ]---
> [6.271293] note: kworker/u12:3[173] exited with preempt_count 1
> [6.277342] Unable to handle kernel paging request at virtual address
> ffd8
>
> It happens while booting, and among other things it requires having platform
> OF drivers marking their `of_driver_id` arrays as `__initconst`, e.g:
>
> static const struct of_device_id some_driver_of[] __initconst = {
> ...
> {},
> };
>
> Given a platform driver that uses deferred probing, these arrays marked as
> `__initconst` could be accessed from a deferred probe path after the init
> section of the kernel has been freed. I have not seen anything in the API
> related deferred probing that can guard from this scenario.
>
> On kernels prior to KASLR the access is not detected, but it can still happen,
> potentially accessing memory that was returned to the page allocator.
>
> On 4.15-rc1, the following shows the ratio between instances of `of_device_id`
> arrays and the number of them which are declared`__initconst`:
>
> $ git grep 'struct of_device_id.*\[\]' | wc -l
> 3089
>
> $ git grep 'struct of_device_id.*\[\]' | grep __initconst | wc -l
> 117
>
> Not all of these instances are platform drivers, but perhaps deferred
> probing with other types of drivers may cause similar issues.
>
> Perhaps it is worthwhile patching stable kernels for the removal of
> `__initconst` on these arrays?
Yes, if those patches are in Linus's tree, that fixes a bug.
> And for the larger question -
>
> Freeing of init sections poses an exploitable vulnerability if that memory
> is not unmapped, _and_ if there are still accesses taking place due to bugs
> of this kind. Linux's build process is supposed to detect references from
> non-freed sections to the freed sections, but clearly this instance has
> not been detected during build, particularly because we have the `__ref`,
> `__refdata`, and `__refconst` attributes which suppress those checks.
>
> Perhaps as a harderning measure, older kernels should be patched with a
> config option for not freeing init sections?
Older kernels should just get the fixes that are in newer kernels :)
If you have specific pointers to commits that resolve these issues, I'll
be glad to queue them up in the stable kernels.
Yes, it is a whack-a-mole fixup, a much better option would be what you
suggest. Perhaps we need to fix the build to properly mark these
section references as errors like other ones are?
thanks,
greg k-h
Use-after-free with deferred driver probing and __initconst
Hi all,
[[ CC'ed: folks relating to the original __*_refok family of attributes,
deferred probing, Open Firmware maintainer, drivers/base/ maintainer,
kernel harderning, LKML ]]
It seems that it is possible to cause a use-after-free in the base driver
platform code using a set of combined circumstances which I describe below.
The instance of the issue happens on a patched 4.4 kernel at a client of
mine.
[6.173692] Process kworker/u12:3 (pid: 173, stack limit =
0xfc3ea92b8000)
[6.180902] Call trace:
[6.183345] [] __of_match_node+0x48/0x8c
[6.188820] [] of_match_node+0x44/0x68
[6.194125] [] of_match_device+0x34/0x48
[6.199603] [] platform_match+0x34/0xa8
[6.204991] [] __device_attach_driver+0x60/0xc8
[6.211077] [] bus_for_each_drv+0x60/0xac
[6.216640] [] __device_attach+0x98/0x124
[6.03] [] device_initial_probe+0x24/0x30
[6.228111] [] bus_probe_device+0x38/0xa0
[6.233677] [] deferred_probe_work_func+0x108/0x128
[6.240111] [] process_one_work+0x268/0x444
[6.245849] [] worker_thread+0x274/0x404
[6.251329] [] kthread+0xe0/0xe8
[6.256114] [] ret_from_fork+0x10/0x50
[6.261415] ---[ end trace fccad0f7d2c2142a ]---
[6.271293] note: kworker/u12:3[173] exited with preempt_count 1
[6.277342] Unable to handle kernel paging request at virtual address
ffd8
It happens while booting, and among other things it requires having platform
OF drivers marking their `of_driver_id` arrays as `__initconst`, e.g:
static const struct of_device_id some_driver_of[] __initconst = {
...
{},
};
Given a platform driver that uses deferred probing, these arrays marked as
`__initconst` could be accessed from a deferred probe path after the init
section of the kernel has been freed. I have not seen anything in the API
related deferred probing that can guard from this scenario.
On kernels prior to KASLR the access is not detected, but it can still happen,
potentially accessing memory that was returned to the page allocator.
On 4.15-rc1, the following shows the ratio between instances of `of_device_id`
arrays and the number of them which are declared`__initconst`:
$ git grep 'struct of_device_id.*\[\]' | wc -l
3089
$ git grep 'struct of_device_id.*\[\]' | grep __initconst | wc -l
117
Not all of these instances are platform drivers, but perhaps deferred
probing with other types of drivers may cause similar issues.
Perhaps it is worthwhile patching stable kernels for the removal of
`__initconst` on these arrays?
And for the larger question -
Freeing of init sections poses an exploitable vulnerability if that memory
is not unmapped, _and_ if there are still accesses taking place due to bugs
of this kind. Linux's build process is supposed to detect references from
non-freed sections to the freed sections, but clearly this instance has
not been detected during build, particularly because we have the `__ref`,
`__refdata`, and `__refconst` attributes which suppress those checks.
Perhaps as a harderning measure, older kernels should be patched with a
config option for not freeing init sections?
--
Dan Aloni
