From: Roberto Sassu <roberto.sassu@huawei.com>
To: Dan Carpenter <dan.carpenter@oracle.com>,
Mimi Zohar <zohar@linux.ibm.com>
Cc: James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.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>,
Silviu Vlasceanu <Silviu.Vlasceanu@huawei.com>
Subject: RE: [PATCH] evm: Fix a small race in init_desc()
Date: Tue, 12 May 2020 13:43:52 +0000 [thread overview]
Message-ID: <c7743ab21a574eeeac40d783e0b8581c@huawei.com> (raw)
In-Reply-To: <20200512131917.GA287386@mwanda>
> From: linux-integrity-owner@vger.kernel.org [mailto:linux-integrity-
> owner@vger.kernel.org] On Behalf Of Dan Carpenter
> Sent: Tuesday, May 12, 2020 3:19 PM
> Subject: [PATCH] evm: Fix a small race in init_desc()
>
> The IS_ERR_OR_NULL() function has two conditions and if we got really
> unlucky we could hit a race where "ptr" started as an error pointer and
> then was set to NULL. Both conditions would be false even though the
> pointer at the end was NULL.
>
> This patch fixes the problem by ensuring that "*tfm" can only be NULL
> or valid. I have introduced a "tmp_tfm" variable to make that work. I
> also reversed a condition and pulled the code in one tab.
>
> Reported-by: Roberto Sassu <roberto.sassu@huawei.com>
> Fixes: 53de3b080d5e: "evm: Check also if *tfm is an error pointer in
> init_desc()"
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> I just had a go at the fix. I'm not super wedded to this solution, but
> I hoped it was nice.
Thanks. I think you can merge both patches in one, as the first one
is not yet pulled.
Roberto
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli
> security/integrity/evm/evm_crypto.c | 44 ++++++++++++++---------------
> 1 file changed, 22 insertions(+), 22 deletions(-)
>
> diff --git a/security/integrity/evm/evm_crypto.c
> b/security/integrity/evm/evm_crypto.c
> index 5d3789edab71f..168c3b78ac47b 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -73,7 +73,7 @@ static struct shash_desc *init_desc(char type, uint8_t
> hash_algo)
> {
> long rc;
> const char *algo;
> - struct crypto_shash **tfm;
> + struct crypto_shash **tfm, *tmp_tfm;
> struct shash_desc *desc;
>
> if (type == EVM_XATTR_HMAC) {
> @@ -91,31 +91,31 @@ static struct shash_desc *init_desc(char type, uint8_t
> hash_algo)
> algo = hash_algo_name[hash_algo];
> }
>
> - if (IS_ERR_OR_NULL(*tfm)) {
> - mutex_lock(&mutex);
> - if (*tfm)
> - goto out;
> - *tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
> - if (IS_ERR(*tfm)) {
> - rc = PTR_ERR(*tfm);
> - pr_err("Can not allocate %s (reason: %ld)\n", algo,
> rc);
> - *tfm = NULL;
> + if (*tfm)
> + goto alloc;
> + mutex_lock(&mutex);
> + if (*tfm)
> + goto unlock;
> +
> + tmp_tfm = crypto_alloc_shash(algo, 0, CRYPTO_NOLOAD);
> + if (IS_ERR(tmp_tfm)) {
> + pr_err("Can not allocate %s (reason: %ld)\n", algo,
> + PTR_ERR(tmp_tfm));
> + mutex_unlock(&mutex);
> + return ERR_CAST(tmp_tfm);
> + }
> + if (type == EVM_XATTR_HMAC) {
> + rc = crypto_shash_setkey(tmp_tfm, evmkey, evmkey_len);
> + if (rc) {
> + crypto_free_shash(tmp_tfm);
> mutex_unlock(&mutex);
> return ERR_PTR(rc);
> }
> - if (type == EVM_XATTR_HMAC) {
> - rc = crypto_shash_setkey(*tfm, evmkey,
> evmkey_len);
> - if (rc) {
> - crypto_free_shash(*tfm);
> - *tfm = NULL;
> - mutex_unlock(&mutex);
> - return ERR_PTR(rc);
> - }
> - }
> -out:
> - mutex_unlock(&mutex);
> }
> -
> + *tfm = tmp_tfm;
> +unlock:
> + mutex_unlock(&mutex);
> +alloc:
> desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
> GFP_KERNEL);
> if (!desc)
> --
> 2.26.2
next prev parent reply other threads:[~2020-05-12 13:43 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 [this message]
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
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