linux-kernel - Re: [PATCH] selinux: no recursive read_lock of policy_rwlock in security_genfs

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Date:	Fri, 20 Jun 2014 19:37:18 -0400
From:	Waiman Long <waiman.long@...com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
CC:	Paul Moore <paul@...l-moore.com>,
	Eric Paris <eparis@...isplace.org>,
	James Morris <james.l.morris@...cle.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH] selinux: no recursive read_lock of policy_rwlock in security_genfs_sid()

On 06/20/2014 01:49 PM, Stephen Smalley wrote:
> On 06/20/2014 01:45 PM, Waiman Long wrote:
>> With introduction of fair queued rwlock, recursive read_lock() may hang
>> the offending process if there is a write_lock() somewhere in between.
>>
>> With recursive read_lock checking enabled, the following error was
>> reported:
>>
>> =============================================
>> [ INFO: possible recursive locking detected ]
>> 3.16.0-rc1 #2 Tainted: G            E
>> ---------------------------------------------
>> load_policy/708 is trying to acquire lock:
>>   (policy_rwlock){.+.+..}, at: [<ffffffff8125b32a>] security_genfs_sid+0x3a/0x170
>>
>> but task is already holding lock:
>>   (policy_rwlock){.+.+..}, at: [<ffffffff8125b48c>] security_fs_use+0x2c/0x110
>>
>> other info that might help us debug this:
>>   Possible unsafe locking scenario:
>>
>>         CPU0
>>         ----
>>    lock(policy_rwlock);
>>    lock(policy_rwlock);
>>
>> This patch fixes the occurrence of recursive read_lock() of
>> policy_rwlock in security_genfs_sid() by adding a 5th argument to
>> indicate if the rwlock has been taken.
>>
>> Signed-off-by: Waiman Long<Waiman.Long@...com>
> Thanks, but I'd prefer to instead create a static helper function in
> services.c that does not take the lock at all, use that function from
> security_fs_use, and leave the extern function unmodified.

On second thought, this is exactly what I want to change the patch. I 
will send out a new one later today.

-Longman
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