linux-kernel - [PATCH 4.18 155/235] evm: Dont deadlock if a crypto algorithm is unavailable

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Date:   Mon, 24 Sep 2018 13:52:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthew Garrett <mjg59@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.18 155/235] evm: Dont deadlock if a crypto algorithm is unavailable

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthew Garrett <mjg59@...gle.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@...gle.com>
Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 crypto/api.c                        |    2 +-
 include/linux/crypto.h              |    5 +++++
 security/integrity/evm/evm_crypto.c |    3 ++-
 3 files changed, 8 insertions(+), 2 deletions(-)

--- a/crypto/api.c
+++ b/crypto/api.c
@@ -229,7 +229,7 @@ static struct crypto_alg *crypto_larval_
 	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 &
--- 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
--- 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
 		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);