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authorEric Biggers <ebiggers@google.com>2020-09-16 21:11:35 -0700
committerEric Biggers <ebiggers@google.com>2020-09-22 06:48:49 -0700
commitac4acb1f4b2b6b7e8d913537cccec8789903e164 (patch)
treee6999a5cae6cb884d844450d19b59da6049186e5 /fs/crypto
parent31114726b69364f3bf8dd945c600ceed4c430f4f (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')
-rw-r--r--fs/crypto/fname.c11
-rw-r--r--fs/crypto/fscrypt_private.h6
-rw-r--r--fs/crypto/hooks.c30
-rw-r--r--fs/crypto/keysetup.c33
-rw-r--r--fs/crypto/policy.c113
5 files changed, 100 insertions, 93 deletions
diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 47bcfddb278b..eb13408b50a7 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -242,11 +242,11 @@ static int base64_decode(const char *src, int len, u8 *dst)
return cp - dst;
}
-bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
- u32 max_len, u32 *encrypted_len_ret)
+bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
+ u32 orig_len, u32 max_len,
+ u32 *encrypted_len_ret)
{
- const struct fscrypt_info *ci = inode->i_crypt_info;
- int padding = 4 << (fscrypt_policy_flags(&ci->ci_policy) &
+ int padding = 4 << (fscrypt_policy_flags(policy) &
FSCRYPT_POLICY_FLAGS_PAD_MASK);
u32 encrypted_len;
@@ -418,7 +418,8 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
return ret;
if (fscrypt_has_encryption_key(dir)) {
- if (!fscrypt_fname_encrypted_size(dir, iname->len,
+ if (!fscrypt_fname_encrypted_size(&dir->i_crypt_info->ci_policy,
+ iname->len,
dir->i_sb->s_cop->max_namelen,
&fname->crypto_buf.len))
return -ENAMETOOLONG;
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index ac3352086ee4..4f5806a3b73d 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -291,8 +291,9 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
/* fname.c */
int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
u8 *out, unsigned int olen);
-bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
- u32 max_len, u32 *encrypted_len_ret);
+bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
+ u32 orig_len, u32 max_len,
+ u32 *encrypted_len_ret);
extern const struct dentry_operations fscrypt_d_ops;
/* hkdf.c */
@@ -592,5 +593,6 @@ bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
const union fscrypt_context *ctx_u,
int ctx_size);
+const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir);
#endif /* _FSCRYPT_PRIVATE_H */
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index a399c54947f2..42f5ee9f592d 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -193,30 +193,24 @@ int fscrypt_prepare_symlink(struct inode *dir, const char *target,
unsigned int len, unsigned int max_len,
struct fscrypt_str *disk_link)
{
- int err;
+ const union fscrypt_policy *policy;
- if (!IS_ENCRYPTED(dir) && !fscrypt_get_dummy_context(dir->i_sb)) {
+ /*
+ * To calculate the size of the encrypted symlink target we need to know
+ * the amount of NUL padding, which is determined by the flags set in
+ * the encryption policy which will be inherited from the directory.
+ */
+ policy = fscrypt_policy_to_inherit(dir);
+ if (policy == NULL) {
+ /* Not encrypted */
disk_link->name = (unsigned char *)target;
disk_link->len = len + 1;
if (disk_link->len > max_len)
return -ENAMETOOLONG;
return 0;
}
-
- /*
- * To calculate the size of the encrypted symlink target we need to know
- * the amount of NUL padding, which is determined by the flags set in
- * the encryption policy which will be inherited from the directory.
- * The easiest way to get access to this is to just load the directory's
- * fscrypt_info, since we'll need it to create the dir_entry anyway.
- *
- * Note: in test_dummy_encryption mode, @dir may be unencrypted.
- */
- err = fscrypt_get_encryption_info(dir);
- if (err)
- return err;
- if (!fscrypt_has_encryption_key(dir))
- return -ENOKEY;
+ if (IS_ERR(policy))
+ return PTR_ERR(policy);
/*
* Calculate the size of the encrypted symlink and verify it won't
@@ -229,7 +223,7 @@ int fscrypt_prepare_symlink(struct inode *dir, const char *target,
* counting it (even though it is meaningless for ciphertext) is simpler
* for now since filesystems will assume it is there and subtract it.
*/
- if (!fscrypt_fname_encrypted_size(dir, len,
+ if (!fscrypt_fname_encrypted_size(policy, len,
max_len - sizeof(struct fscrypt_symlink_data),
&disk_link->len))
return -ENAMETOOLONG;
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 47f19061ba10..d3c3e5d9b41f 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -547,7 +547,7 @@ out:
/**
* fscrypt_get_encryption_info() - set up an inode's encryption key
- * @inode: the inode to set up the key for
+ * @inode: the inode to set up the key for. Must be encrypted.
*
* Set up ->i_crypt_info, if it hasn't already been done.
*
@@ -569,18 +569,8 @@ int fscrypt_get_encryption_info(struct inode *inode)
res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
if (res < 0) {
- const union fscrypt_context *dummy_ctx =
- fscrypt_get_dummy_context(inode->i_sb);
-
- if (IS_ENCRYPTED(inode) || !dummy_ctx) {
- fscrypt_warn(inode,
- "Error %d getting encryption context",
- res);
- return res;
- }
- /* Fake up a context for an unencrypted directory */
- res = fscrypt_context_size(dummy_ctx);
- memcpy(&ctx, dummy_ctx, res);
+ fscrypt_warn(inode, "Error %d getting encryption context", res);
+ return res;
}
res = fscrypt_policy_from_context(&policy, &ctx, res);
@@ -627,17 +617,14 @@ EXPORT_SYMBOL(fscrypt_get_encryption_info);
int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
bool *encrypt_ret)
{
- int err;
+ const union fscrypt_policy *policy;
u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
- if (!IS_ENCRYPTED(dir) && fscrypt_get_dummy_context(dir->i_sb) == NULL)
+ policy = fscrypt_policy_to_inherit(dir);
+ if (policy == NULL)
return 0;
-
- err = fscrypt_get_encryption_info(dir);
- if (err)
- return err;
- if (!fscrypt_has_encryption_key(dir))
- return -ENOKEY;
+ if (IS_ERR(policy))
+ return PTR_ERR(policy);
if (WARN_ON_ONCE(inode->i_mode == 0))
return -EINVAL;
@@ -654,9 +641,7 @@ int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
*encrypt_ret = true;
get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
- return fscrypt_setup_encryption_info(inode,
- &dir->i_crypt_info->ci_policy,
- nonce,
+ return fscrypt_setup_encryption_info(inode, policy, nonce,
IS_CASEFOLDED(dir) &&
S_ISDIR(inode->i_mode));
}
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);