Commit 6e1918cf authored by Daniel Rosenberg's avatar Daniel Rosenberg Committed by Eric Biggers
Browse files

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: default avatarDaniel 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: default avatarEric Biggers <ebiggers@google.com>
parent 1b3b827e

Documentation/filesystems/fscrypt.rst

+3 −1
Original line number Diff line number Diff line
@@ -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

fs/crypto/hooks.c

+28 −0
Original line number Diff line number Diff line
@@ -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)

fs/crypto/policy.c

+7 −0
Original line number Diff line number Diff line
@@ -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;

}

fs/inode.c

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

include/linux/fscrypt.h

+9 −0
Original line number Diff line number Diff line
@@ -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,

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