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
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -513,7 +513,9 @@
- ``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
--- 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
--- 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
--- 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..3984eadd 100644
--- 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,
