4.9-stable review patch. If anyone has any objections, please let me know.
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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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.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 @@ -215,7 +215,7 @@ struct crypto_alg *crypto_larval_lookup( 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 & --- a/include/linux/crypto.h +++ b/include/linux/crypto.h @@ -109,6 +109,11 @@ #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 @@ -94,7 +94,8 @@ 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);