[PATCH] security/keys: fix slab-out-of-bounds in key_task_permission

[Chen Ridong]

On 2024/10/8 10:41, Jarkko Sakkinen wrote:
> On Tue, 2024-10-08 at 09:40 +0800, chenridong wrote:
>>
>>
>> On 2024/10/8 7:15, Jarkko Sakkinen wrote:
>>> Hi,
>>>
>>> Revisit...
>>>
>>> On Fri, 2024-09-13 at 07:09 +0000, Chen Ridong wrote:
>>>> We meet the same issue with the LINK, which reads memory out of
>>>> bounds:
>>>
>>> Never ever use pronoun "we" in a commit message in any possible
>>> sentence. Instead always use passive imperative.
>>>
>>> What you probably want to say is:
>>>
>>> "KASAN reports an out of bounds read:"
>>>
>>> Right?
>>>
>>
>> Yes.
>>
>>>> BUG: KASAN: slab-out-of-bounds in __kuid_val
>>>> include/linux/uidgid.h:36
>>>> BUG: KASAN: slab-out-of-bounds in uid_eq
>>>> include/linux/uidgid.h:63
>>>> [inline]
>>>> BUG: KASAN: slab-out-of-bounds in key_task_permission+0x394/0x410
>>>> security/keys/permission.c:54
>>>> Read of size 4 at addr ffff88813c3ab618 by task stress-ng/4362
>>>>
>>>> CPU: 2 PID: 4362 Comm: stress-ng Not tainted 5.10.0-14930-
>>>> gafbffd6c3ede #15
>>>> Call Trace:
>>>>    __dump_stack lib/dump_stack.c:82 [inline]
>>>>    dump_stack+0x107/0x167 lib/dump_stack.c:123
>>>>    print_address_description.constprop.0+0x19/0x170
>>>> mm/kasan/report.c:400
>>>>    __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
>>>>    kasan_report+0x3a/0x50 mm/kasan/report.c:585
>>>>    __kuid_val include/linux/uidgid.h:36 [inline]
>>>>    uid_eq include/linux/uidgid.h:63 [inline]
>>>>    key_task_permission+0x394/0x410 security/keys/permission.c:54
>>>>    search_nested_keyrings+0x90e/0xe90 security/keys/keyring.c:793
>>>
>>> Snip all below away:
>>>
>>>>    keyring_search_rcu+0x1b6/0x310 security/keys/keyring.c:922
>>>>    search_cred_keyrings_rcu+0x111/0x2e0
>>>> security/keys/process_keys.c:459
>>>>    search_process_keyrings_rcu+0x1d/0x310
>>>> security/keys/process_keys.c:544
>>>>    lookup_user_key+0x782/0x12e0 security/keys/process_keys.c:762
>>>>    keyctl_invalidate_key+0x20/0x190 security/keys/keyctl.c:434
>>>>    __do_sys_keyctl security/keys/keyctl.c:1978 [inline]
>>>>    __se_sys_keyctl+0x1de/0x5b0 security/keys/keyctl.c:1880
>>>>    do_syscall_64+0x30/0x40 arch/x86/entry/common.c:46
>>>>    entry_SYSCALL_64_after_hwframe+0x67/0xd1
>>>
>>> Remember to cut only the relevant part of the stack trace to make
>>> this
>>> commit message more compact and readable.
>>>
>> Thank you, I will do that.
>>
>>>>
>>>> However, we can't reproduce this issue.
>>>> After our analysis, it can make this issue by following steps.
>>>> 1.As syzkaller reported, the memory is allocated for struct
>>>
>>> "1."
>>>
>>>>     assoc_array_shortcut in the
>>>> assoc_array_insert_into_terminal_node
>>>>     functions.
>>>> 2.In the search_nested_keyrings, when we go through the slots in
>>>> a
>>>> node,
>>>>     (bellow tag ascend_to_node), and the slot ptr is meta and
>>>>     node->back_pointer != NULL, we will proceed to
>>>> descend_to_node.
>>>>     However, there is an exception. If node is the root, and one
>>>> of the
>>>>     slots points to a shortcut, it will be treated as a keyring.
>>>> 3.Whether the ptr is keyring decided by keyring_ptr_is_keyring
>>>> function.
>>>>     However, KEYRING_PTR_SUBTYPE is 0x2UL, the same as
>>>>     ASSOC_ARRAY_PTR_SUBTYPE_MASK,
>>>> 4.As mentioned above, If a slot of the root is a shortcut, it may
>>>> be
>>>>     mistakenly be transferred to a key*, leading to an read out-
>>>> of-
>>>> bounds
>>>>     read.
>>>
>>> Delete the whole list and write a description of the problem and
>>> why
>>> your change resolves it.
>>>
>>> As per code change, let's layout it something more readable first:
>>>
>>> /* Traverse branches into depth: */
>>> if (assoc_array_ptr_is_meta(ptr)) {
>>> 	if (node->back_pointer ||
>>> assoc_array_ptr_is_shortcut(ptr))
>>> 		goto descend_to_node;
>>> }
>>>
>>> So one thing that should be explained just to make the description
>>> rigid is why 'ptr' is passed to assoc_array_ptr_is_shortcut() and
>>> not 'node'. I'm actually 100% sure about that part, which kind
>>> of supports my view here, right? :-)
>>>
>>> The first part of the if-statement obviously filters out everything
>>> that is not root (when it comes to 'node'). Explain the second
>>> part.
>>> At that point it is know that node is a root node, so continue from
>>> there.
>>>
>>> BR, Jarkko
>>>
>>
>> Thank you for your patience.
>> I will update soon.
> 
> Yeah of course, and I did low quality job earlier no issues admitting
> that, so let's do this correct this time. I just try to describe
> what I'm seeing as accurately as I can :-)
> 
> Here it is just important to get the explanation and the code change
> in-sync so that it is easy to verify and compare them, given that it
> is quite sensitive functionality and somewhat obfuscated peace of code
> showing age.
> 
> Also I think a good is to make sure that every fix will leave it at
> least a bit cleaner state. From this basis I proposed a bit different
> layout for the code.
> 
>>
>> Best regards,
>> Ridong
> 
> BR,Jarkko

Hi, Jarkko, I sent the v2 several days ago.
I don't know whether you have received it. I hope you have time to look 
into it, and I am still looking forward to your reply.

v2: 
https://lore.kernel.org/linux-kernel/20241008124639.70000-1-chenridong@huaweicloud.com/

Best regards,
Ridong