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

Sasha Levin
2018-09-15T01:34:39Z

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