Re: [PATCH] kunit: string-stream: Fix a UAF bug in kunit_init_suite()

[Jinjie Ruan]

On 2024/11/9 21:02, Kuan-Wei Chiu wrote:
> On Sat, Nov 09, 2024 at 08:40:30PM +0800, Kuan-Wei Chiu wrote:
>> Hi Jinjie,
>>
>> On Thu, Oct 24, 2024 at 05:43:03PM +0800, Jinjie Ruan wrote:
>>> In kunit_debugfs_create_suite(), if alloc_string_stream() fails in the
>>> kunit_suite_for_each_test_case() loop, the "suite->log = stream"
>>> has assigned before, and the error path only free the suite->log's stream
>>> memory but not set it to NULL in string_stream_destroy(), so the later
>>> string_stream_clear() of suite->log in kunit_init_suite() will cause
>>> below UAF bug.
>>>
>>> Set stream pointer to NULL after free in string_stream_destroy()
>>> to fix it.
>>>
>>> 	Unable to handle kernel paging request at virtual address 006440150000030d
>>> 	Mem abort info:
>>> 	  ESR = 0x0000000096000004
>>> 	  EC = 0x25: DABT (current EL), IL = 32 bits
>>> 	  SET = 0, FnV = 0
>>> 	  EA = 0, S1PTW = 0
>>> 	  FSC = 0x04: level 0 translation fault
>>> 	Data abort info:
>>> 	  ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
>>> 	  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
>>> 	  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
>>> 	[006440150000030d] address between user and kernel address ranges
>>> 	Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
>>> 	Dumping ftrace buffer:
>>> 	   (ftrace buffer empty)
>>> 	Modules linked in: iio_test_gts industrialio_gts_helper cfg80211 rfkill ipv6 [last unloaded: iio_test_gts]
>>> 	CPU: 5 UID: 0 PID: 6253 Comm: modprobe Tainted: G    B   W        N 6.12.0-rc4+ #458
>>> 	Tainted: [B]=BAD_PAGE, [W]=WARN, [N]=TEST
>>> 	Hardware name: linux,dummy-virt (DT)
>>> 	pstate: 40000005 (nZcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>> 	pc : string_stream_clear+0x54/0x1ac
>>> 	lr : string_stream_clear+0x1a8/0x1ac
>>> 	sp : ffffffc080b47410
>>> 	x29: ffffffc080b47410 x28: 006440550000030d x27: ffffff80c96b5e98
>>> 	x26: ffffff80c96b5e80 x25: ffffffe461b3f6c0 x24: 0000000000000003
>>> 	x23: ffffff80c96b5e88 x22: 1ffffff019cdf4fc x21: dfffffc000000000
>>> 	x20: ffffff80ce6fa7e0 x19: 032202a80000186d x18: 0000000000001840
>>> 	x17: 0000000000000000 x16: 0000000000000000 x15: ffffffe45c355cb4
>>> 	x14: ffffffe45c35589c x13: ffffffe45c03da78 x12: ffffffb810168e75
>>> 	x11: 1ffffff810168e74 x10: ffffffb810168e74 x9 : dfffffc000000000
>>> 	x8 : 0000000000000004 x7 : 0000000000000003 x6 : 0000000000000001
>>> 	x5 : ffffffc080b473a0 x4 : 0000000000000000 x3 : 0000000000000000
>>> 	x2 : 0000000000000001 x1 : ffffffe462fbf620 x0 : dfffffc000000000
>>> 	Call trace:
>>> 	 string_stream_clear+0x54/0x1ac
>>> 	 __kunit_test_suites_init+0x108/0x1d8
>>> 	 kunit_exec_run_tests+0xb8/0x100
>>> 	 kunit_module_notify+0x400/0x55c
>>> 	 notifier_call_chain+0xfc/0x3b4
>>> 	 blocking_notifier_call_chain+0x68/0x9c
>>> 	 do_init_module+0x24c/0x5c8
>>> 	 load_module+0x4acc/0x4e90
>>> 	 init_module_from_file+0xd4/0x128
>>> 	 idempotent_init_module+0x2d4/0x57c
>>> 	 __arm64_sys_finit_module+0xac/0x100
>>> 	 invoke_syscall+0x6c/0x258
>>> 	 el0_svc_common.constprop.0+0x160/0x22c
>>> 	 do_el0_svc+0x44/0x5c
>>> 	 el0_svc+0x48/0xb8
>>> 	 el0t_64_sync_handler+0x13c/0x158
>>> 	 el0t_64_sync+0x190/0x194
>>> 	Code: f9400753 d2dff800 f2fbffe0 d343fe7c (38e06b80)
>>> 	---[ end trace 0000000000000000 ]---
>>> 	Kernel panic - not syncing: Oops: Fatal exception
>>>
>>> Cc: stable@xxxxxxxxxxxxxxx
>>> Fixes: a3fdf784780c ("kunit: string-stream: Decouple string_stream from kunit")
>>> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
>>> ---
>>>  lib/kunit/string-stream.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/lib/kunit/string-stream.c b/lib/kunit/string-stream.c
>>> index 54f4fdcbfac8..00ad518b730b 100644
>>> --- a/lib/kunit/string-stream.c
>>> +++ b/lib/kunit/string-stream.c
>>> @@ -178,6 +178,7 @@ void string_stream_destroy(struct string_stream *stream)
>>>  
>>>  	string_stream_clear(stream);
>>>  	kfree(stream);
>>> +	stream = NULL;
>>
>> Thanks for proposing the fix. However, I don't believe it fully
>> resolves the UAF issue. Changing the stream pointer value within
>> string_stream_destroy() doesn't update the caller's stream pointer, so
>> the issue remains.
>>
>> I think the correct approach would be to set the log pointer to NULL in
>> the error path of kunit_debugfs_create_suite() to address the issue.
>> Let me know if I've missed something or overlooked an obvious detail.
>>
> BTW, since alloc_string_stream() returns -ENOMEM on error rather than
> NULL, it's best for the caller to check it with IS_ERR() instead of
> IS_ERR_OR_NULL(). It's not a big issue, but I can send a cleanup patch
> later to address this.

Yes, I also notice it, but It's not a big issue. Thank you very much!

> 
> Regards,
> Kuan-Wei