| Message ID | 20180601230244.138560-1-mjg59@google.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
On Fri, Jun 01, 2018 at 04:02:43PM -0700, Matthew Garrett wrote: > Trying to instantiate a non-existent crypto algorithm will cause the > kernel to trigger a module load. If EVM appraisal is enabled, this will > in turn trigger appraisal of the module, which will fail because the > crypto algorithm isn't available. Add a CRYPTO_NOLOAD flag and skip > module loading if it's set, and add that flag in the EVM case. > > Signed-off-by: Matthew Garrett <mjg59@google.com> I don't get it. Without your patch it will fail because the EVM appraisal fails. With your patch it will fail because there is no algorithm registered. So what's the difference? Cheers,
On Sat, Jun 2, 2018 at 8:54 AM Herbert Xu <herbert@gondor.apana.org.au> wrote: > > On Fri, Jun 01, 2018 at 04:02:43PM -0700, Matthew Garrett wrote: > > Trying to instantiate a non-existent crypto algorithm will cause the > > kernel to trigger a module load. If EVM appraisal is enabled, this will > > in turn trigger appraisal of the module, which will fail because the > > crypto algorithm isn't available. Add a CRYPTO_NOLOAD flag and skip > > module loading if it's set, and add that flag in the EVM case. > > > > Signed-off-by: Matthew Garrett <mjg59@google.com> > > I don't get it. Without your patch it will fail because the > EVM appraisal fails. With your patch it will fail because there > is no algorithm registered. So what's the difference? Without my patch it will deadlock as it recursively calls back into EVM to perform the module appraisal. Sorry, the description was unclear on that point.
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 a46fba322340..ccafc9468611 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);
Trying to instantiate a non-existent crypto algorithm will cause the kernel to trigger a module load. If EVM appraisal is enabled, this will in turn trigger appraisal of the module, which will fail because the crypto algorithm isn't available. Add a CRYPTO_NOLOAD flag and skip module loading if it's set, and add that flag in the EVM case. 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(-)