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authorMatthew Garrett <mjg59@google.com>2018-06-08 14:57:42 -0700
committerMimi Zohar <zohar@linux.vnet.ibm.com>2018-07-18 07:27:22 -0400
commite2861fa71641c6414831d628a1f4f793b6562580 (patch)
treee832d4eac8fb33e2838a76cc9457bd3c2d6a2065
parentac2409a521f7ec5978fd582567398d19f4a2fdbd (diff)
downloadlinux-e2861fa71641c6414831d628a1f4f793b6562580.tar.bz2
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>
-rw-r--r--crypto/api.c2
-rw-r--r--include/linux/crypto.h5
-rw-r--r--security/integrity/evm/evm_crypto.c3
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
@@ -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 b60524310855..c20e3142b541 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);