linux-kernel - Re: security: double-free in superblock

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Message-Id: <201703231949.EDJ81789.FHMQOFLFOtVOJS@I-love.SAKURA.ne.jp>
Date:   Thu, 23 Mar 2017 19:49:12 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     dvyukov@...gle.com, paul@...l-moore.com, sds@...ho.nsa.gov,
        eparis@...isplace.org, james.l.morris@...cle.com, serge@...lyn.com,
        keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com, selinux@...ho.nsa.gov,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     syzkaller@...glegroups.com
Subject: Re: security: double-free in superblock_doinit

Dmitry Vyukov wrote:
> Hello,
> 
> I've got the following double-free report in superblock_doinit while
> running syzkaller fuzzer.
> Note the preceding injected failure in kmalloc, most likely that the root cause.

Thank you for reporting.

selinux_parse_opts_str() and smack_parse_opts_str() forgot to set
opts->mnt_opts to NULL after kfree() at

if (!opts->mnt_opts_flags) {
	kfree(opts->mnt_opts);
	goto out_err;
}

and caused double free at

if (opts->mnt_opts)
	for (i = 0; i < opts->num_mnt_opts; i++)
		kfree(opts->mnt_opts[i]);

in security_free_mnt_opts().