linux-kernel - Re: [PATCH v2] security: device

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+5PVA6NrEhRfaFJgCmH6P3Wznme4W2bPk8=WgmmpM0WSbLjxA@mail.gmail.com>
Date:	Thu, 3 Sep 2015 09:56:05 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, Felipe Balbi <balbi@...com>,
	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v2] security: device_cgroup: fix RCU lockdep splat

On Wed, Sep 2, 2015 at 8:14 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Sep 02, 2015 at 12:24:50PM -0400, Tejun Heo wrote:
>> cc'ing Paul.
>>
>> On Wed, Sep 02, 2015 at 08:12:28AM -0500, Felipe Balbi wrote:
>> > while booting AM437x device, the following splat
>> > triggered:
>> >
>> > [   12.005238] ===============================
>> > [   12.009749] [ INFO: suspicious RCU usage. ]
>> > [   12.014116] 4.2.0-next-20150831 #1154 Not tainted
>> > [   12.019050] -------------------------------
>> > [   12.023408] security/device_cgroup.c:405 device_cgroup:verify_new_ex called without proper synchronization!
>> ...
>> > [   12.128326] [<c0317a04>] (verify_new_ex) from [<c0317f50>] (devcgroup_access_write+0x374/0x658)
>> > [   12.137426] [<c0317f50>] (devcgroup_access_write) from [<c00d2800>] (cgroup_file_write+0x28/0x1bc)
>> > [   12.146796] [<c00d2800>] (cgroup_file_write) from [<c01f1670>] (kernfs_fop_write+0xc0/0x1b8)
>> > [   12.155620] [<c01f1670>] (kernfs_fop_write) from [<c0177c94>] (__vfs_write+0x1c/0xd8)
>> > [   12.163783] [<c0177c94>] (__vfs_write) from [<c0178594>] (vfs_write+0x90/0x16c)
>> > [   12.171426] [<c0178594>] (vfs_write) from [<c0178db4>] (SyS_write+0x44/0x9c)
>> > [   12.178806] [<c0178db4>] (SyS_write) from [<c000f680>] (ret_fast_syscall+0x0/0x1c)
>>
>> This shouldn't be happening because devcgroup_access_write() always
>> grabs devcgroup_mutex.  Looking at the log, the culprit seems to be
>> f78f5b90c4ff ("rcu: Rename rcu_lockdep_assert() to
>> RCU_LOCKDEP_WARN()").  It missed the bang for the second test while
>> inverting it, so adding rcu_read_lock() isn't the right fix here.
>>
>> Paul, can you please fix it?
>
> Gah!  Please see below.
>
>                                                         Thanx, Paul
>
> ------------------------------------------------------------------------
>
> security/device_cgroup: Fix RCU_LOCKDEP_WARN() condition
>
> f78f5b90c4ff ("rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()")
> introduced a bug by incorrectly inverting the condition when moving from
> rcu_lockdep_assert() to RCU_LOCKDEP_WARN().  This commit therefore fixes
> the inversion.
>
> Reported-by: Felipe Balbi <balbi@...com>
> Reported-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Serge Hallyn <serge@...lyn.com>

Just tested this patch without Felipe's previous version on all my
machines.  The splat is indeed gone.

Tested-by: Josh Boyer <jwboyer@...oraproject.org>

josh

>
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 73455089feef..03c1652c9a1f 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -401,7 +401,7 @@ static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
>         bool match = false;
>
>         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
> -                        lockdep_is_held(&devcgroup_mutex),
> +                        !lockdep_is_held(&devcgroup_mutex),
>                          "device_cgroup:verify_new_ex called without proper synchronization");
>
>         if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/