Re: [PATCH] ima: fix deadlock when traversing "ima_default_rules".

Guozihua (Scott)
2024-05-08T02:06:13Z

On 2024/5/7 19:54, Mimi Zohar wrote:
> On Tue, 2024-05-07 at 09:37 +0000, GUO Zihua wrote:
>> From: liqiong <liqiong@nfschina.com>
>>
>> [ Upstream commit eb0782bbdfd0d7c4786216659277c3fd585afc0e ]
>>
>> The current IMA ruleset is identified by the variable "ima_rules"
>> that default to "&ima_default_rules". When loading a custom policy
>> for the first time, the variable is updated to "&ima_policy_rules"
>> instead. That update isn't RCU-safe, and deadlocks are possible.
>> Indeed, some functions like ima_match_policy() may loop indefinitely
>> when traversing "ima_default_rules" with list_for_each_entry_rcu().
>>
>> When iterating over the default ruleset back to head, if the list
>> head is "ima_default_rules", and "ima_rules" have been updated to
>> "&ima_policy_rules", the loop condition (&entry->list != ima_rules)
>> stays always true, traversing won't terminate, causing a soft lockup
>> and RCU stalls.
>>
>> Introduce a temporary value for "ima_rules" when iterating over
>> the ruleset to avoid the deadlocks.
>>
>> Addition:
>>
>> A rcu_read_lock pair is added within ima_update_policy_flag to avoid
>> suspicious RCU usage warning. This pair of RCU lock was added with
>> commit 4f2946aa0c45 ("IMA: introduce a new policy option
>> func=SETXATTR_CHECK") on mainstream.
>>
>> Signed-off-by: liqiong <liqiong@nfschina.com>
>> Reviewed-by: THOBY Simon <Simon.THOBY@viveris.fr>
>> Fixes: 38d859f991f3 ("IMA: policy can now be updated multiple times")
>> Reported-by: kernel test robot <lkp@intel.com> (Fix sparse: incompatible types in comparison expression.)
>> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
>> Sig=ned-off-by: GUO Zihua <guozihua@huawei.com>
>
> Hi Scott,
>
> I'm confused by this patch. Is it meant for upstream?
>
> thanks,
>
> Mimi
>
It's a backport from upstream.

--
Best
GUO Zihua