evm: Don't deadlock if a crypto algorithm is unavailable

When EVM attempts to appraise a file signed with a crypto algorithm the
kernel doesn't have support for, it will cause the kernel to trigger a
module load. If the EVM policy includes appraisal of kernel modules this
will in turn call back into EVM - since EVM is holding a lock until the
crypto initialisation is complete, this triggers a deadlock. Add a
CRYPTO_NOLOAD flag and skip module loading if it's set, and add that flag
in the EVM case in order to fail gracefully with an error message
instead of deadlocking.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

diff --git a/crypto/api.c b/crypto/api.c
index 0ee632b..7aca9f8 100644 (file)
--- 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 6eb0610..e8839d3 100644 (file)
--- a/include/linux/crypto.h
+++ b/include/linux/crypto.h
@@ -113,6 +113,11 @@
 #define CRYPTO_ALG_OPTIONAL_KEY                0x00004000
 
 /*
+ * Don't trigger module loading
+ */
+#define CRYPTO_NOLOAD                  0x00008000
+
+/*
  * Transform masks and values (for crt_flags).
  */
 #define CRYPTO_TFM_NEED_KEY            0x00000001

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index b605243..c20e314 100644 (file)
--- 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);