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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: 53de3b080d ("evm: Check also if *tfm is an error pointer in init_desc()")
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>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Dan Carpenter 2020-05-12 16:19:17 +03:00 committed by Mimi Zohar
parent 770f60586d
commit 8433856947
1 changed files with 22 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

44
security/integrity/evm/evm_crypto.c
View File

@ -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)