From: Mimi Zohar <zohar@linux.ibm.com>
To: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>,
Roberto Sassu <roberto.sassu@huawei.com>,
Dan Carpenter <dan.carpenter@oracle.com>
Cc: James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
Dmitry Kasatkin <dmitry.kasatkin@nokia.com>,
"linux-integrity@vger.kernel.org"
<linux-integrity@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>,
"kernel-janitors@vger.kernel.org"
<kernel-janitors@vger.kernel.org>
Subject: Re: [PATCH v2] evm: Fix a small race in init_desc()
Date: Thu, 14 May 2020 14:21:50 -0400 [thread overview]
Message-ID: <1589480510.4757.5.camel@linux.ibm.com> (raw)
In-Reply-To: <19452750e36d462088f4fca3d627a090@huawei.com>
On Thu, 2020-05-14 at 07:11 +0000, Krzysztof Struczynski wrote:
> > > From: Dan Carpenter [mailto:dan.carpenter@oracle.com]
> > > This patch avoids a kernel panic due to accessing an error pointer set
> > > by crypto_alloc_shash(). It occurs especially when there are many
> > > files that require an unsupported algorithm, as it would increase the
> > > likelihood of the following race condition.
> > >
> > > Imagine we have two threads and in the first thread
> > > crypto_alloc_shash() fails and returns an error pointer.
> > >
> > > *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
> > > if (IS_ERR(*tfm)) {
> > > rc = PTR_ERR(*tfm); <--- FIRST THREAD HERE!
> > > pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
> > > *tfm = NULL;
> > >
> > > And the second thread is here:
> > >
> > > if (*tfm == NULL) { <--- SECOND THREAD HERE!
> > > mutex_lock(&mutex);
> > > if (*tfm)
> > > goto out;
> > >
> > > Since "*tfm" is non-NULL, we assume that it is valid and that leads to
> > > a crash when it dereferences "*tfm".
> > >
> > > desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
> > > ^^^^
> > >
> > > This patch fixes the problem by introducing a temporary "tmp_tfm" and
> > > only setting "*tfm" at the very end after everything has succeeded.
> > > The other change is that I reversed the initial "if (!*tfm) {"
> > > condition and pull the code in one indent level.
> > >
> > > Cc: stable@vger.kernel.org
> > > Fixes: d46eb3699502b ("evm: crypto hash replaced by shash")
> > > Reported-by: Roberto Sassu <roberto.sassu@huawei.com>
> > > Reported-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
> > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> >
> > Acked-by: Roberto Sassu <roberto.sassu@huawei.com>
>
> Acked-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Thanks, Roberto and Krzysztof.
This patch is now queued in the "fixes" branch.
Mimi
prev parent reply other threads:[~2020-05-14 18:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 10:48 [bug report] evm: Check also if *tfm is an error pointer in init_desc() Dan Carpenter
2020-05-12 11:31 ` Roberto Sassu
2020-05-12 12:34 ` Dan Carpenter
2020-05-12 12:45 ` Roberto Sassu
2020-05-12 13:04 ` Dan Carpenter
2020-05-12 13:08 ` Roberto Sassu
2020-05-12 13:19 ` [PATCH] evm: Fix a small race " Dan Carpenter
2020-05-12 13:43 ` Roberto Sassu
2020-05-12 17:47 ` [PATCH v2] " Dan Carpenter
2020-05-14 6:47 ` Roberto Sassu
2020-05-14 7:11 ` Krzysztof Struczynski
2020-05-14 18:21 ` Mimi Zohar [this message]
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