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Subject[PATCH 2/5] evm: Check also if *tfm is an error pointer in init_desc()
Date
The mutex in init_desc(), introduced by commit 97426f985729 ("evm: prevent
racing during tfm allocation") prevents two tasks to concurrently set *tfm.
However, checking if *tfm is NULL is not enough, as crypto_alloc_shash()
can return an error pointer. The following sequence can happen:

Task A: *tfm = crypto_alloc_shash() <= error pointer
Task B: if (*tfm == NULL) <= *tfm is not NULL, use it
Task B: rc = crypto_shash_init(desc) <= panic
Task A: *tfm = NULL

This patch uses the IS_ERR_OR_NULL macro to determine whether or not a new
crypto context must be created.

Cc: stable@vger.kernel.org
Fixes: 97426f985729 ("evm: prevent racing during tfm allocation")
Co-developed-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
security/integrity/evm/evm_crypto.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 35682852ddea..77ad1e5a93e4 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -91,7 +91,7 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
algo = hash_algo_name[hash_algo];
}

- if (*tfm == NULL) {
+ if (IS_ERR_OR_NULL(*tfm)) {
mutex_lock(&mutex);
if (*tfm)
goto out;
--
2.17.1
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