evm: Don't deadlock if a crypto algorithm is unavailable (e2861fa7) · Commits · 戴 / test

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>

crypto/api.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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 &

include/linux/crypto.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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).
		*/

security/integrity/evm/evm_crypto.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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);

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