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

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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>
This commit is contained in:
Matthew Garrett 2018-06-08 14:57:42 -07:00 committed by Mimi Zohar
parent ac2409a521
commit e2861fa716
3 changed files with 8 additions and 2 deletions
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2
crypto/api.c
View File

@ -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 &

5
include/linux/crypto.h
View File

@ -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).
*/

3
security/integrity/evm/evm_crypto.c
View File

@ -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);