Re: [PATCH] fix security_release_secctx seems broken

[Konstantin Khlebnikov]

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@xxxxxxxxxxxxxxxx>
>
> 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.