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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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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).
*/