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

[chenridong]

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.

Best regards,
Ridong