[PATCH v2 1/3] evm: check hash algorithm passed to init_desc()

[Roberto Sassu]

This patch prevents memory access beyond the evm_tfm array by checking the
validity of the index (hash algorithm) passed to init_desc(). The hash
algorithm can be arbitrarily set if the security.ima xattr type is not
EVM_XATTR_HMAC.

Fixes: 5feeb61183dde ("evm: Allow non-SHA1 digital signatures")
Signed-off-by: Roberto Sassu <roberto.sa...@huawei.com>
Cc: sta...@vger.kernel.org
---
 security/integrity/evm/evm_crypto.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/security/integrity/evm/evm_crypto.c 
b/security/integrity/evm/evm_crypto.c
index e11564eb645b..82a38e801ee4 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -89,6 +89,9 @@ static struct shash_desc *init_desc(char type, uint8_t 
hash_algo)
                tfm = &hmac_tfm;
                algo = evm_hmac;
        } else {
+               if (hash_algo >= HASH_ALGO__LAST)
+                       return ERR_PTR(-EINVAL);
+
                tfm = &evm_tfm[hash_algo];
                algo = hash_algo_name[hash_algo];
        }
-- 
2.17.1