[PATCH AUTOSEL 4.9 05/34] evm: Don't deadlock if a crypto algorithm is unavailable

[Sasha Levin]

From: Matthew Garrett <mj...@google.com>

[ Upstream commit e2861fa71641c6414831d628a1f4f793b6562580 ]

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 <mj...@google.com>
Acked-by: Herbert Xu <herb...@gondor.apana.org.au>
Signed-off-by: Mimi Zohar <zo...@linux.vnet.ibm.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.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 bbc147cb5dec..abf53e67e3d8 100644
--- a/crypto/api.c
+++ b/crypto/api.c
@@ -215,7 +215,7 @@ struct crypto_alg *crypto_larval_lookup(const char *name, 
u32 type, u32 mask)
        type &= mask;
 
        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 8edb3ba6f640..9de26962338e 100644
--- a/include/linux/crypto.h
+++ b/include/linux/crypto.h
@@ -108,6 +108,11 @@
  */
 #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 bf663915412e..6fcbd8e99baf 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -94,7 +94,8 @@ 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