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

[Chen Ridong]

On 2024/9/19 4:57, Jarkko Sakkinen wrote:
> On Wed Sep 18, 2024 at 10:30 AM EEST, Chen Ridong wrote:
>>
>>
>> On 2024/9/15 21:59, Jarkko Sakkinen wrote:
>>> On Sun Sep 15, 2024 at 3:55 AM EEST, Chen Ridong wrote:
>>>>
>>>>
>>>> On 2024/9/14 19:33, Jarkko Sakkinen wrote:
>>>>> On Fri Sep 13, 2024 at 10:09 AM EEST, Chen Ridong wrote:
>>>>>> We meet the same issue with the LINK, which reads memory out of bounds:
>>>>>
>>>>> Nit: don't use "we" anywhere".
>>>>>
>>>>> Tbh, I really don't understand the sentence above. I don't what
>>>>> "the same issue with the LINK" really is.
>>>>>
>>>>
>>>> Hello, Jarkko.
>>>> I apologize for any confusion caused.
>>>>
>>>> I've encountered a bug reported by syzkaller. I also found the same bug
>>>> reported at this LINK:
>>>> https://syzkaller.appspot.com/bug?id=68a5e206c2a8e08d317eb83f05610c0484ad10b9.
>>>>
>>>>>> 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
>>>>>>     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
>>>>>>
>>>>>> However, we can't reproduce this issue.
>>>>>
>>>>> "The issue cannot be easily reproduced but by analyzing the code
>>>>> it can be broken into following steps:"
>>>>
>>>> Thank you for your correction.
>>>> Does this patch address the issue correctly? Is this patch acceptable?
>>>
>>> I only comment new patch versions so not giving any promises but I can
>>> say that it is I think definitely in the correct direction :-)
>>>
>>> BR, Jarkko
>>
>> Hello, Jarkko. I have reproduced this issue. It can be reproduced by
>> following these steps:
>>
>> 1. Add the helper patch.
>>
>> @@ -205,6 +205,9 @@ static void hash_key_type_and_desc(struct
>> keyring_index_key *index_key)
>>           else if (index_key->type == &key_type_keyring && (hash &
>> fan_mask) != 0)
>>                   hash = (hash + (hash << level_shift)) & ~fan_mask;
>>           index_key->hash = hash;
>> +       if ((index_key->hash & 0xff) == 0xe6) {
>> +                       pr_err("hash_key_type_and_desc: type %s %s
>> 0x%x\n",  index_key->type->name, index_key->description, index_key->hash);
>> +       }
>>    }
>>
>> 2. Pick up the inputs whose hash is xxe6 using the following cmd. If a
>> key's hash is xxe6, it will be printed.
>>
>> for ((i=0; i<=10000; i++)); do ./test_key user user$i "Some payload"; done
>>
>> You have complile test_key whith following code.
>>
>> #include <sys/types.h>
>> #include <keyutils.h>
>> #include <stdint.h>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <string.h>
>>
>> int
>> main(int argc, char *argv[])
>> {
>>      key_serial_t key;
>>
>>      if (argc != 4) {
>> 	   fprintf(stderr, "Usage: %s type description payload\n",
>> 			   argv[0]);
>> 	   exit(EXIT_FAILURE);
>>      }
>>
>>      key = add_key(argv[1], argv[2], argv[3], strlen(argv[3]),
>> 			   KEY_SPEC_SESSION_KEYRING);
>>      if (key == -1) {
>> 	   perror("add_key");
>> 	   exit(EXIT_FAILURE);
>>      }
>>
>>      printf("Key ID is %jx\n", (uintmax_t) key);
>>
>>      exit(EXIT_SUCCESS);
>> }
>>
>>
>> 3. Have more than 32 inputs now. their hashes are xxe6.
>> eg.
>> hash_key_type_and_desc: type user user438 0xe3033fe6
>> hash_key_type_and_desc: type user user526 0xeb7eade6
>> ...
>> hash_key_type_and_desc: type user user9955 0x44bc99e6
>>
>> 4. Reboot and add the keys obtained from step 3.
>> When adding keys to the ROOT that their hashes are all xxe6, and up to
>> 16, the ROOT has keys with hashes that are not xxe6 (e.g., slot 0), so
>> the keys are dissimilar. The ROOT will then split NODE A without using a
>> shortcut. When NODE A is filled with keys that have hashes of xxe6, the
>> keys are similar. NODE A will split with a shortcut.
>>
>> As my analysis, if a slot of the root is a shortcut(slot 6), it may be
>> mistakenly be transferred to a key*, leading to an read out-of-bounds read.
>>
>>                         NODE A
>>                 +------>+---+
>>         ROOT    |       | 0 | xxe6
>>         +---+   |       +---+
>>    xxxx | 0 | shortcut  :   : xxe6
>>         +---+   |       +---+
>>    xxe6 :   :   |       |   | xxe6
>>         +---+   |       +---+
>>         | 6 |---+       :   : xxe6
>>         +---+           +---+
>>    xxe6 :   :           | f | xxe6
>>         +---+           +---+
>>    xxe6 | f |
>>         +---+
>>
>> 5. cat /proc/keys. and the issue is reproduced.
> 
> Hi, I'll try to run through your procedure next week and give my comments.
> Thanks for doing this.
> 
> BR, Jarkko

Hi, Jarkko, have you run these procedure?
I have tested this patch with LTP and a pressure test(stress-ng --key), 
and this patch have fixed this issue. Additionally, no new bugs have 
been found so far.

I am looking forward to your reply.

Best regards,
Ridong