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fscrypt: don't allow v1 policies with casefolding

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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>
This commit is contained in:
Daniel Rosenberg 2020-01-20 14:31:56 -08:00 • committed by Eric Biggers
parent 1b3b827ee5
commit 6e1918cfb2
5 changed files with 49 additions and 2 deletions
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9
include/linux/fscrypt.h
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@ -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,