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

BugLink: https://bugs.launchpad.net/bugs/1836117
[ 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/crypto/api.c b/crypto/api.c
index 2a2479d168aacbe3e31799a2c713614b71e6805b..ff7a7852bb17acc90535be965727f42a2a9ef7e4 100644 (file)
--- a/crypto/api.c
+++ b/crypto/api.c
@@ -216,7 +216,7 @@ struct crypto_alg *crypto_larval_lookup(const char *name, u32 type, u32 mask)
        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 29c4257f9c5b14c3c66e2e57eef573f9a2ff7a10..5e14fac088d565953ff396526470031f21bf6043 100644 (file)
--- a/include/linux/crypto.h
+++ b/include/linux/crypto.h
@@ -112,6 +112,11 @@
  */
 #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 729f45454384aeea5a722898c59f48a83063d9a4..cf4efa8cb3ca7719f78b3439efe080334d34e537 100644 (file)
--- 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);