evm: check hash algorithm passed to init_desc()

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.sassu@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 3 insertions, 0 deletions

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];
         }