| Message ID | 20180608215743.224253-2-mjg59@google.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
On Fri, Jun 8, 2018 at 2:57 PM Matthew Garrett <mjg59@google.com> wrote: > > 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. Hi Herbert, Does this explain the problem sufficiently?
On Fri, Jun 08, 2018 at 02:57:42PM -0700, Matthew Garrett wrote: > 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>
On Wed, 2018-06-13 at 14:33 +0800, Herbert Xu wrote: > On Fri, Jun 08, 2018 at 02:57:42PM -0700, Matthew Garrett wrote: > > 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> Thanks! This patch and "evm: Allow non-SHA1 digital signatures" are now queued in the next-integrity-queued branch. Mimi
diff --git a/crypto/api.c b/crypto/api.c index 0ee632bba064..7aca9f86c5f3 100644 --- a/crypto/api.c +++ b/crypto/api.c @@ -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 & diff --git a/include/linux/crypto.h b/include/linux/crypto.h index 6eb06101089f..e8839d3a7559 100644 --- 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 494da5fcc092..bea847dc0919 100644 --- a/security/integrity/evm/evm_crypto.c +++ b/security/integrity/evm/evm_crypto.c @@ -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);
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> --- crypto/api.c | 2 +- include/linux/crypto.h | 5 +++++ security/integrity/evm/evm_crypto.c | 3 ++- 3 files changed, 8 insertions(+), 2 deletions(-)