Trying to instantiate a non-existent crypto algorithm will cause the
kernel to trigger a module load. If EVM appraisal is enabled, this will
in turn trigger appraisal of the module, which will fail because the
crypto algorithm isn't available. Add a CRYPTO_NOLOAD flag and skip
module loading if it's set, and add that flag in the EVM case.

Signed-off-by: Matthew Garrett <mj...@google.com>
---
 crypto/api.c                        | 2 +-
 include/linux/crypto.h              | 5 +++++
 security/integrity/evm/evm_crypto.c | 3 ++-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/crypto/api.c b/crypto/api.c
index 0ee632bba064..7aca9f86c5f3 100644
--- a/crypto/api.c
+++ b/crypto/api.c
@@ -229,7 +229,7 @@ static struct crypto_alg *crypto_larval_lookup(const char 
*name, u32 type,
        mask &= ~(CRYPTO_ALG_LARVAL | CRYPTO_ALG_DEAD);
 
        alg = crypto_alg_lookup(name, type, mask);
-       if (!alg) {
+       if (!alg && !(mask & CRYPTO_NOLOAD)) {
                request_module("crypto-%s", name);
 
                if (!((type ^ CRYPTO_ALG_NEED_FALLBACK) & mask &
diff --git a/include/linux/crypto.h b/include/linux/crypto.h
index 6eb06101089f..e8839d3a7559 100644
--- a/include/linux/crypto.h
+++ b/include/linux/crypto.h
@@ -112,6 +112,11 @@
  */
 #define CRYPTO_ALG_OPTIONAL_KEY                0x00004000
 
+/*
+ * Don't trigger module loading
+ */
+#define CRYPTO_NOLOAD                  0x00008000
+
 /*
  * Transform masks and values (for crt_flags).
  */
diff --git a/security/integrity/evm/evm_crypto.c 
b/security/integrity/evm/evm_crypto.c
index a46fba322340..ccafc9468611 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -97,7 +97,8 @@ static struct shash_desc *init_desc(char type)
                mutex_lock(&mutex);
                if (*tfm)
                        goto out;
-               *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
+               *tfm = crypto_alloc_shash(algo, 0,
+                                         CRYPTO_ALG_ASYNC | CRYPTO_NOLOAD);
                if (IS_ERR(*tfm)) {
                        rc = PTR_ERR(*tfm);
                        pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
-- 
2.17.1.1185.g55be947832-goog

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