linux-kernel - Re: [PATCH] autofs: sanity check status reported with AUTOFS_DEV_IOCTL

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Message-ID: <87fuf07k84.fsf@notabene.neil.brown.name>
Date:   Fri, 16 Jun 2017 12:13:47 +1000
From:   NeilBrown <neilb@...e.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Ian Kent <raven@...maw.net>, LKML <linux-kernel@...r.kernel.org>,
        autofs mailing list <autofs@...r.kernel.org>
Subject: Re: [PATCH] autofs: sanity check status reported with AUTOFS_DEV_IOCTL_FAIL

On Thu, Jun 15 2017, Andrew Morton wrote:

> On Wed, 07 Jun 2017 12:08:38 +1000 NeilBrown <neilb@...e.com> wrote:
>
>> 
>> If a positive status is passed with the AUTOFS_DEV_IOCTL_FAIL
>> ioctl, autofs4_d_automount() will return
>>    ERR_PTR(status)
>> with that status to follow_automount(), which will then
>> dereference an invalid pointer.
>> 
>> So treat a positive status the same as zero, and map
>> to ENOENT.
>> 
>> See comment in systemd src/core/automount.c::automount_send_ready().
>> 
>> ...
>>
>> --- a/fs/autofs4/dev-ioctl.c
>> +++ b/fs/autofs4/dev-ioctl.c
>> @@ -344,7 +344,7 @@ static int autofs_dev_ioctl_fail(struct file *fp,
>>  	int status;
>>  
>>  	token = (autofs_wqt_t) param->fail.token;
>> -	status = param->fail.status ? param->fail.status : -ENOENT;
>> +	status = param->fail.status < 0 ? param->fail.status : -ENOENT;
>>  	return autofs4_wait_release(sbi, token, status);
>>  }
>
> Sounds serious.  Was the absence of a cc:stable deliberate?

You need CAP_SYS_ADMIN to  get the ioctl even looked at.  Doesn't that
mean the bug can only be triggered by a process that could easily do
worse?

Or do containers allow admins to give out CAP_SYS_ADMIN to untrusted
people??  I haven't been keeping up.

Given how simple the patch is, it probably makes sense to add a
cc:stable, just in case.

Thanks,
NeilBrown

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