diff options
author | Eric Biggers <ebiggers@google.com> | 2020-09-16 21:11:35 -0700 |
---|---|---|
committer | Eric Biggers <ebiggers@google.com> | 2020-09-22 06:48:49 -0700 |
commit | ac4acb1f4b2b6b7e8d913537cccec8789903e164 (patch) | |
tree | e6999a5cae6cb884d844450d19b59da6049186e5 /fs/crypto/policy.c | |
parent | 31114726b69364f3bf8dd945c600ceed4c430f4f (diff) |
fscrypt: handle test_dummy_encryption in more logical way
The behavior of the test_dummy_encryption mount option is that when a
new file (or directory or symlink) is created in an unencrypted
directory, it's automatically encrypted using a dummy encryption policy.
That's it; in particular, the encryption (or lack thereof) of existing
files (or directories or symlinks) doesn't change.
Unfortunately the implementation of test_dummy_encryption is a bit weird
and confusing. When test_dummy_encryption is enabled and a file is
being created in an unencrypted directory, we set up an encryption key
(->i_crypt_info) for the directory. This isn't actually used to do any
encryption, however, since the directory is still unencrypted! Instead,
->i_crypt_info is only used for inheriting the encryption policy.
One consequence of this is that the filesystem ends up providing a
"dummy context" (policy + nonce) instead of a "dummy policy". In
commit ed318a6cc0b6 ("fscrypt: support test_dummy_encryption=v2"), I
mistakenly thought this was required. However, actually the nonce only
ends up being used to derive a key that is never used.
Another consequence of this implementation is that it allows for
'inode->i_crypt_info != NULL && !IS_ENCRYPTED(inode)', which is an edge
case that can be forgotten about. For example, currently
FS_IOC_GET_ENCRYPTION_POLICY on an unencrypted directory may return the
dummy encryption policy when the filesystem is mounted with
test_dummy_encryption. That seems like the wrong thing to do, since
again, the directory itself is not actually encrypted.
Therefore, switch to a more logical and maintainable implementation
where the dummy encryption policy inheritance is done without setting up
keys for unencrypted directories. This involves:
- Adding a function fscrypt_policy_to_inherit() which returns the
encryption policy to inherit from a directory. This can be a real
policy, a dummy policy, or no policy.
- Replacing struct fscrypt_dummy_context, ->get_dummy_context(), etc.
with struct fscrypt_dummy_policy, ->get_dummy_policy(), etc.
- Making fscrypt_fname_encrypted_size() take an fscrypt_policy instead
of an inode.
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
Acked-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20200917041136.178600-13-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/crypto/policy.c')
-rw-r--r-- | fs/crypto/policy.c | 113 |
1 files changed, 69 insertions, 44 deletions
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c index 4ff893f7b030..97cf07543651 100644 --- a/fs/crypto/policy.c +++ b/fs/crypto/policy.c @@ -32,6 +32,14 @@ bool fscrypt_policies_equal(const union fscrypt_policy *policy1, return !memcmp(policy1, policy2, fscrypt_policy_size(policy1)); } +static const union fscrypt_policy * +fscrypt_get_dummy_policy(struct super_block *sb) +{ + if (!sb->s_cop->get_dummy_policy) + return NULL; + return sb->s_cop->get_dummy_policy(sb); +} + static bool fscrypt_valid_enc_modes(u32 contents_mode, u32 filenames_mode) { if (contents_mode == FSCRYPT_MODE_AES_256_XTS && @@ -628,6 +636,25 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child) } EXPORT_SYMBOL(fscrypt_has_permitted_context); +/* + * Return the encryption policy that new files in the directory will inherit, or + * NULL if none, or an ERR_PTR() on error. If the directory is encrypted, also + * ensure that its key is set up, so that the new filename can be encrypted. + */ +const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir) +{ + int err; + + if (IS_ENCRYPTED(dir)) { + err = fscrypt_require_key(dir); + if (err) + return ERR_PTR(err); + return &dir->i_crypt_info->ci_policy; + } + + return fscrypt_get_dummy_policy(dir->i_sb); +} + /** * fscrypt_set_context() - Set the fscrypt context of a new inode * @inode: a new inode @@ -672,31 +699,28 @@ EXPORT_SYMBOL_GPL(fscrypt_set_context); * @sb: the filesystem on which test_dummy_encryption is being specified * @arg: the argument to the test_dummy_encryption option. * If no argument was specified, then @arg->from == NULL. - * @dummy_ctx: the filesystem's current dummy context (input/output, see below) + * @dummy_policy: the filesystem's current dummy policy (input/output, see + * below) * * Handle the test_dummy_encryption mount option by creating a dummy encryption - * context, saving it in @dummy_ctx, and adding the corresponding dummy - * encryption key to the filesystem. If the @dummy_ctx is already set, then + * policy, saving it in @dummy_policy, and adding the corresponding dummy + * encryption key to the filesystem. If the @dummy_policy is already set, then * instead validate that it matches @arg. Don't support changing it via * remount, as that is difficult to do safely. * - * The reason we use an fscrypt_context rather than an fscrypt_policy is because - * we mustn't generate a new nonce each time we access a dummy-encrypted - * directory, as that would change the way filenames are encrypted. - * - * Return: 0 on success (dummy context set, or the same context is already set); - * -EEXIST if a different dummy context is already set; + * Return: 0 on success (dummy policy set, or the same policy is already set); + * -EEXIST if a different dummy policy is already set; * or another -errno value. */ int fscrypt_set_test_dummy_encryption(struct super_block *sb, const substring_t *arg, - struct fscrypt_dummy_context *dummy_ctx) + struct fscrypt_dummy_policy *dummy_policy) { const char *argstr = "v2"; const char *argstr_to_free = NULL; struct fscrypt_key_specifier key_spec = { 0 }; int version; - union fscrypt_context *ctx = NULL; + union fscrypt_policy *policy = NULL; int err; if (arg->from) { @@ -706,12 +730,12 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb, } if (!strcmp(argstr, "v1")) { - version = FSCRYPT_CONTEXT_V1; + version = FSCRYPT_POLICY_V1; key_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR; memset(key_spec.u.descriptor, 0x42, FSCRYPT_KEY_DESCRIPTOR_SIZE); } else if (!strcmp(argstr, "v2")) { - version = FSCRYPT_CONTEXT_V2; + version = FSCRYPT_POLICY_V2; key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER; /* key_spec.u.identifier gets filled in when adding the key */ } else { @@ -719,21 +743,8 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb, goto out; } - if (dummy_ctx->ctx) { - /* - * Note: if we ever make test_dummy_encryption support - * specifying other encryption settings, such as the encryption - * modes, we'll need to compare those settings here. - */ - if (dummy_ctx->ctx->version == version) - err = 0; - else - err = -EEXIST; - goto out; - } - - ctx = kzalloc(sizeof(*ctx), GFP_KERNEL); - if (!ctx) { + policy = kzalloc(sizeof(*policy), GFP_KERNEL); + if (!policy) { err = -ENOMEM; goto out; } @@ -742,18 +753,18 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb, if (err) goto out; - ctx->version = version; - switch (ctx->version) { - case FSCRYPT_CONTEXT_V1: - ctx->v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS; - ctx->v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS; - memcpy(ctx->v1.master_key_descriptor, key_spec.u.descriptor, + policy->version = version; + switch (policy->version) { + case FSCRYPT_POLICY_V1: + policy->v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS; + policy->v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS; + memcpy(policy->v1.master_key_descriptor, key_spec.u.descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE); break; - case FSCRYPT_CONTEXT_V2: - ctx->v2.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS; - ctx->v2.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS; - memcpy(ctx->v2.master_key_identifier, key_spec.u.identifier, + case FSCRYPT_POLICY_V2: + policy->v2.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS; + policy->v2.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS; + memcpy(policy->v2.master_key_identifier, key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE); break; default: @@ -761,11 +772,19 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb, err = -EINVAL; goto out; } - dummy_ctx->ctx = ctx; - ctx = NULL; + + if (dummy_policy->policy) { + if (fscrypt_policies_equal(policy, dummy_policy->policy)) + err = 0; + else + err = -EEXIST; + goto out; + } + dummy_policy->policy = policy; + policy = NULL; err = 0; out: - kfree(ctx); + kfree(policy); kfree(argstr_to_free); return err; } @@ -783,10 +802,16 @@ EXPORT_SYMBOL_GPL(fscrypt_set_test_dummy_encryption); void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep, struct super_block *sb) { - const union fscrypt_context *ctx = fscrypt_get_dummy_context(sb); + const union fscrypt_policy *policy = fscrypt_get_dummy_policy(sb); + int vers; - if (!ctx) + if (!policy) return; - seq_printf(seq, "%ctest_dummy_encryption=v%d", sep, ctx->version); + + vers = policy->version; + if (vers == FSCRYPT_POLICY_V1) /* Handle numbering quirk */ + vers = 1; + + seq_printf(seq, "%ctest_dummy_encryption=v%d", sep, vers); } EXPORT_SYMBOL_GPL(fscrypt_show_test_dummy_encryption); |