linux-kernel - Re: CVE-2016-7097 causes acl leak

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Date:   Sun, 11 Dec 2016 16:34:31 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        aneesh.kumar@...ux.vnet.ibm.com, Jan Kara <jack@...e.cz>
Subject: Re: CVE-2016-7097 causes acl leak

On Mon, Dec 5, 2016 at 9:16 AM, Mark Salyzyn <salyzyn@...roid.com> wrote:
> Commit 073931017b49d9458aa351605b43a7e34598caef has several occurrences of
> an acl leak.
>
> posix_acl_update_mode(inose, &mode, &acl);
>
> . . .
>
> posix_acl_release(acl);
>
>
> acl is NULLed in posix_acl_update_mode to signal caller to not update the
> acl; but because it is nulled, it is never released.

I think you blame the wrong commit, this leak exists before that commit.
Looks like we should just release it before NULL'ing.

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 5955220..edd862a 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -648,8 +648,10 @@ int posix_acl_update_mode(struct inode *inode,
umode_t *mode_p,
        error = posix_acl_equiv_mode(*acl, &mode);
        if (error < 0)
                return error;
-       if (error == 0)
+       if (error == 0) {
+               posix_acl_release(*acl);
                *acl = NULL;
+       }
        if (!in_group_p(inode->i_gid) &&
            !capable_wrt_inode_uidgid(inode, CAP_FSETID))
                mode &= ~S_ISGID;