fscrypt_put_encryption_info() is only called when evicting an inode, so
the 'struct fscrypt_info *ci' parameter is always NULL, and there cannot
be races with other threads.  This was cruft left over from the broken
key revocation code.  Remove the unused parameter and the cmpxchg().

Also remove the #ifdefs around the fscrypt_put_encryption_info() calls,
since fscrypt_notsupp.h defines a no-op stub for it.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Filesystems don't need fscrypt_fname_encrypted_size() anymore, so
unexport it and move it to fscrypt_private.h.

We also never calculate the encrypted size of a filename without having
the fscrypt_info present since it is needed to know the amount of
NUL-padding which is determined by the encryption policy, and also we
will always truncate the NUL-padding to the maximum filename length.
Therefore, also make fscrypt_fname_encrypted_size() assume that the
fscrypt_info is present, and make it truncate the returned length to the
specified max_len.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Previously fscrypt_fname_alloc_buffer() was used to allocate buffers for
both presented (decrypted or encoded) and encrypted filenames.  That was
confusing, because it had to allocate the worst-case size for either,
e.g. including NUL-padding even when it was meaningless.

But now that fscrypt_setup_filename() no longer calls it, it is only
used in the ->get_link() and ->readdir() paths, which specifically want
a buffer for presented filenames.  Therefore, switch the behavior over
to allocating the buffer for presented filenames only.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fscrypt_fname_usr_to_disk() sounded very generic but was actually only
used to encrypt symlinks.  Remove it now that all filesystems have been
switched over to fscrypt_encrypt_symlink().

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Filesystems also have duplicate code to support ->get_link() on
encrypted symlinks.  Factor it out into a new function
fscrypt_get_symlink().  It takes in the contents of the encrypted
symlink on-disk and provides the target (decrypted or encoded) that
should be returned from ->get_link().

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Currently, filesystems supporting fscrypt need to implement some tricky
logic when creating encrypted symlinks, including handling a peculiar
on-disk format (struct fscrypt_symlink_data) and correctly calculating
the size of the encrypted symlink.  Introduce helper functions to make
things a bit easier:

- fscrypt_prepare_symlink() computes and validates the size the symlink
  target will require on-disk.
- fscrypt_encrypt_symlink() creates the encrypted target if needed.

The new helpers actually fix some subtle bugs.  First, when checking
whether the symlink target was too long, filesystems didn't account for
the fact that the NUL padding is meant to be truncated if it would cause
the maximum length to be exceeded, as is done for filenames in
directories.  Consequently users would receive ENAMETOOLONG when
creating symlinks close to what is supposed to be the maximum length.
For example, with EXT4 with a 4K block size, the maximum symlink target
length in an encrypted directory is supposed to be 4093 bytes (in
comparison to 4095 in an unencrypted directory), but in
FS_POLICY_FLAGS_PAD_32-mode only up to 4064 bytes were accepted.

Second, symlink targets of "." and ".." were not being encrypted, even
though they should be, as these names are special in *directory entries*
but not in symlink targets.  Fortunately, we can fix this simply by
starting to encrypt them, as old kernels already accept them in
encrypted form.

Third, the output string length the filesystems were providing when
doing the actual encryption was incorrect, as it was forgotten to
exclude 'sizeof(struct fscrypt_symlink_data)'.  Fortunately though, this
bug didn't make a difference.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fscrypt_dummy_context_enabled() accesses ->s_cop, which now is only set
when the filesystem is built with encryption support.  This didn't
actually matter because no filesystems called it.  However, it will
start being used soon, so fix it by moving it from fscrypt.h to
fscrypt_supp.h and stubbing it out in fscrypt_notsupp.h.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fscrypt_control_page() is already split into two versions depending on
whether the filesystem is being built with encryption support or not.
Move them into the appropriate headers.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fscrypt_has_encryption_key() is already split into two versions
depending on whether the filesystem is being built with encryption
support or not.  Move them into the appropriate headers.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Pull fscrypt updates from Ted Ts'o:
 "Lots of cleanups, mostly courtesy by Eric Biggers"

* tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/fscrypt:
  fscrypt: lock mutex before checking for bounce page pool
  fscrypt: add a documentation file for filesystem-level encryption
  ext4: switch to fscrypt_prepare_setattr()
  ext4: switch to fscrypt_prepare_lookup()
  ext4: switch to fscrypt_prepare_rename()
  ext4: switch to fscrypt_prepare_link()
  ext4: switch to fscrypt_file_open()
  fscrypt: new helper function - fscrypt_prepare_setattr()
  fscrypt: new helper function - fscrypt_prepare_lookup()
  fscrypt: new helper function - fscrypt_prepare_rename()
  fscrypt: new helper function - fscrypt_prepare_link()
  fscrypt: new helper function - fscrypt_file_open()
  fscrypt: new helper function - fscrypt_require_key()
  fscrypt: remove unneeded empty fscrypt_operations structs
  fscrypt: remove ->is_encrypted()
  fscrypt: switch from ->is_encrypted() to IS_ENCRYPTED()
  fs, fscrypt: add an S_ENCRYPTED inode flag
  fscrypt: clean up include file mess