fscrypt: don't allow v1 policies with casefolding

Casefolded encrypted directories will use a new dirhash method that
requires a secret key.  If the directory uses a v2 encryption policy,
it's easy to derive this key from the master key using HKDF.  However,
v1 encryption policies don't provide a way to derive additional keys.

Therefore, don't allow casefolding on directories that use a v1 policy.
Specifically, make it so that trying to enable casefolding on a
directory that has a v1 policy fails, trying to set a v1 policy on a
casefolded directory fails, and trying to open a casefolded directory
that has a v1 policy (if one somehow exists on-disk) fails.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
[EB: improved commit message, updated fscrypt.rst, and other cleanups]
Link: https://lore.kernel.org/r/20200120223201.241390-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 9c53336..380a1be 100644 (file)
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -513,7 +513,9 @@ FS_IOC_SET_ENCRYPTION_POLICY can fail with the following errors:
 - ``EEXIST``: the file is already encrypted with an encryption policy
   different from the one specified
 - ``EINVAL``: an invalid encryption policy was specified (invalid
-  version, mode(s), or flags; or reserved bits were set)
+  version, mode(s), or flags; or reserved bits were set); or a v1
+  encryption policy was specified but the directory has the casefold
+  flag enabled (casefolding is incompatible with v1 policies).
 - ``ENOKEY``: a v2 encryption policy was specified, but the key with
   the specified ``master_key_identifier`` has not been added, nor does
   the process have the CAP_FOWNER capability in the initial user

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 4081aae..fd4e5ae 100644 (file)
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -122,6 +122,34 @@ int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
 
+/**
+ * fscrypt_prepare_setflags() - prepare to change flags with FS_IOC_SETFLAGS
+ * @inode: the inode on which flags are being changed
+ * @oldflags: the old flags
+ * @flags: the new flags
+ *
+ * The caller should be holding i_rwsem for write.
+ *
+ * Return: 0 on success; -errno if the flags change isn't allowed or if
+ *        another error occurs.
+ */
+int fscrypt_prepare_setflags(struct inode *inode,
+                            unsigned int oldflags, unsigned int flags)
+{
+       struct fscrypt_info *ci;
+       int err;
+
+       if (IS_ENCRYPTED(inode) && (flags & ~oldflags & FS_CASEFOLD_FL)) {
+               err = fscrypt_require_key(inode);
+               if (err)
+                       return err;
+               ci = inode->i_crypt_info;
+               if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
+                       return -EINVAL;
+       }
+       return 0;
+}
+
 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
                              unsigned int max_len,
                              struct fscrypt_str *disk_link)

diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index f1cff83..cf2a9d2 100644 (file)
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -124,6 +124,13 @@ static bool fscrypt_supported_v1_policy(const struct fscrypt_policy_v1 *policy,
                                        policy->filenames_encryption_mode))
                return false;
 
+       if (IS_CASEFOLDED(inode)) {
+               /* With v1, there's no way to derive dirhash keys. */
+               fscrypt_warn(inode,
+                            "v1 policies can't be used on casefolded directories");
+               return false;
+       }
+
        return true;
 }
 

diff --git a/fs/inode.c b/fs/inode.c
index 96d62d9..ea15c6d 100644 (file)
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -12,6 +12,7 @@
 #include <linux/security.h>
 #include <linux/cdev.h>
 #include <linux/memblock.h>
+#include <linux/fscrypt.h>
 #include <linux/fsnotify.h>
 #include <linux/mount.h>
 #include <linux/posix_acl.h>
@@ -2252,7 +2253,7 @@ int vfs_ioc_setflags_prepare(struct inode *inode, unsigned int oldflags,
            !capable(CAP_LINUX_IMMUTABLE))
                return -EPERM;
 
-       return 0;
+       return fscrypt_prepare_setflags(inode, oldflags, flags);
 }
 EXPORT_SYMBOL(vfs_ioc_setflags_prepare);
 

diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 6fe8d0f..3984ead 100644 (file)
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -263,6 +263,8 @@ extern int __fscrypt_prepare_rename(struct inode *old_dir,
                                    unsigned int flags);
 extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
                                    struct fscrypt_name *fname);
+extern int fscrypt_prepare_setflags(struct inode *inode,
+                                   unsigned int oldflags, unsigned int flags);
 extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
                                     unsigned int max_len,
                                     struct fscrypt_str *disk_link);
@@ -519,6 +521,13 @@ static inline int __fscrypt_prepare_lookup(struct inode *dir,
        return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_prepare_setflags(struct inode *inode,
+                                          unsigned int oldflags,
+                                          unsigned int flags)
+{
+       return 0;
+}
+
 static inline int __fscrypt_prepare_symlink(struct inode *dir,
                                            unsigned int len,
                                            unsigned int max_len,