Commit 60e463f0 authored by Eric Biggers's avatar Eric Biggers
Browse files

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: default avatarEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230208062107.199831-2-ebiggers@kernel.org
parent 6d796c50

fs/crypto/fscrypt_private.h

+1 −0
Original line number Diff line number Diff line
@@ -651,6 +651,7 @@ bool fscrypt_policies_equal(const union fscrypt_policy *policy1, 
			    const union fscrypt_policy *policy2);

int fscrypt_policy_to_key_spec(const union fscrypt_policy *policy,

			       struct fscrypt_key_specifier *key_spec);

const union fscrypt_policy *fscrypt_get_dummy_policy(struct super_block *sb);

bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,

			      const struct inode *inode);

int fscrypt_policy_from_context(union fscrypt_policy *policy_u,

fs/crypto/keysetup.c

+23 −2
Original line number Diff line number Diff line
@@ -438,6 +438,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci, 
				     bool need_dirhash_key,

				     struct fscrypt_master_key **mk_ret)

{

	struct super_block *sb = ci->ci_inode->i_sb;

	struct fscrypt_key_specifier mk_spec;

	struct fscrypt_master_key *mk;

	int err;
@@ -450,8 +451,28 @@ static int setup_file_encryption_key(struct fscrypt_info *ci, 
	if (err)

		return err;



	mk = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);

	if (!mk) {

	mk = fscrypt_find_master_key(sb, &mk_spec);

	if (unlikely(!mk)) {

		const union fscrypt_policy *dummy_policy =

			fscrypt_get_dummy_policy(sb);



		/*

		 * Add the test_dummy_encryption key on-demand.  In principle,

		 * it should be added at mount time.  Do it here instead so that

		 * the individual filesystems don't need to worry about adding

		 * this key at mount time and cleaning up on mount failure.

		 */

		if (dummy_policy &&

		    fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {

			struct fscrypt_dummy_policy tmp = { dummy_policy };



			err = fscrypt_add_test_dummy_key(sb, &tmp);

			if (err)

				return err;

			mk = fscrypt_find_master_key(sb, &mk_spec);

		}

	}

	if (unlikely(!mk)) {

		if (ci->ci_policy.version != FSCRYPT_POLICY_V1)

			return -ENOKEY;

fs/crypto/policy.c

+1 −2
Original line number Diff line number Diff line
@@ -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;