linux-kernel - Re: [PATCH] fix security_release

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Message-ID: <ff77bdc9-e642-113d-dbde-f4d0770fff00@yandex-team.ru>
Date:   Wed, 4 Oct 2017 12:29:37 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     James Morris <jmorris@...ei.org>,
        Casey Schaufler <casey@...aufler-ca.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Stephen Smalley <sds@...ho.nsa.gov>
Subject: Re: [PATCH] fix security_release_secctx seems broken



On 04.10.2017 09:17, James Morris wrote:
> On Tue, 19 Sep 2017, Casey Schaufler wrote:
> 
>> Subject: [PATCH] fix security_release_secctx seems broken
>>
>> security_inode_getsecurity() provides the text string value
>> of a security attribute. It does not provide a "secctx".
>> The code in xattr_getsecurity() that calls security_inode_getsecurity()
>> and then calls security_release_secctx() happened to work because
>> SElinux and Smack treat the attribute and the secctx the same way.
>> It fails for cap_inode_getsecurity(), because that module has no
>> secctx that ever needs releasing. It turns out that Smack is the
>> one that's doing things wrong by not allocating memory when instructed
>> to do so by the "alloc" parameter.
>>
>> The fix is simple enough. Change the security_release_secctx() to
>> kfree() because it isn't a secctx being returned by
>> security_inode_getsecurity(). Change Smack to allocate the string when
>> told to do so.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> 
> Looks good to me.  I wonder why security_release_secctx was used in the
> first place? (it arrived via commit 42492594)
>  > Konstantin: how did you trigger this?

Just "getcap /bin/ping" is enough to tigger leak if file has capabilities.
Selinux shouldn't be loaded because its release_secctx hook call kfree.

But sometimes it takes some time for kmemleak to find leak. Presumably
because stale poiner stays on stack which could be reused nowdays.

> 
> I plan to send this to Linus for -rc4 unless anyone has objections.
> 
>