fscrypt: add the test dummy encryption key on-demand

When the key for an inode is not found but the inode is using the
test_dummy_encryption policy, automatically add the
test_dummy_encryption key to the filesystem keyring.  This eliminates
the need for all the individual filesystems to do this at mount time,
which is a bit tricky to clean up from on failure.

Note: this covers the call to fscrypt_find_master_key() from inode key
setup, but not from the fscrypt ioctls.  So, this isn't *exactly* the
same as the key being present from the very beginning.  I think we can
tolerate that, though, since the inode key setup caller is the only one
that actually matters in the context of test_dummy_encryption.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230208062107.199831-2-ebiggers@kernel.org

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 893661b52376..69dca4ff5f48 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -53,8 +53,7 @@ int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,
 	}
 }
 
-static const union fscrypt_policy *
-fscrypt_get_dummy_policy(struct super_block *sb)
+const union fscrypt_policy *fscrypt_get_dummy_policy(struct super_block *sb)
 {
 	if (!sb->s_cop->get_dummy_policy)
 		return NULL;