talos-op-linux/fs/crypto, branch master

fscrypt: improve format of no-key names

2020-01-22T22:50:03+00:00

When an encrypted directory is listed without the key, the filesystem must show "no-key names" that uniquely identify directory entries, are at most 255 (NAME_MAX) bytes long, and don't contain '/' or '\0'. Currently, for short names the no-key name is the base64 encoding of the ciphertext filename, while for long names it's the base64 encoding of the ciphertext filename's dirhash and second-to-last 16-byte block. This format has the following problems: - Since it doesn't always include the dirhash, it's incompatible with directories that will use a secret-keyed dirhash over the plaintext filenames. In this case, the dirhash won't be computable from the ciphertext name without the key, so it instead must be retrieved from the directory entry and always included in the no-key name. Casefolded encrypted directories will use this type of dirhash. - It's ambiguous: it's possible to craft two filenames that map to the same no-key name, since the method used to abbreviate long filenames doesn't use a proper cryptographic hash function. Solve both these problems by switching to a new no-key name format that is the base64 encoding of a variable-length structure that contains the dirhash, up to 149 bytes of the ciphertext filename, and (if any bytes remain) the SHA-256 of the remaining bytes of the ciphertext filename. This ensures that each no-key name contains everything needed to find the directory entry again, contains only legal characters, doesn't exceed NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only take the performance hit of SHA-256 on very long filenames. Note: this change does *not* address the existing issue where users can modify the 'dirhash' part of a no-key name and the filesystem may still accept the name. Signed-off-by: Daniel Rosenberg [EB: improved comments and commit message, fixed checking return value of base64_decode(), check for SHA-256 error, continue to set disk_name for short names to keep matching simpler, and many other cleanups] Link: https://lore.kernel.org/r/20200120223201.241390-7-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: clarify what is meant by a per-file key

2020-01-22T22:49:56+00:00

Now that there's sometimes a second type of per-file key (the dirhash key), clarify some function names, macros, and documentation that specifically deal with per-file *encryption* keys. Link: https://lore.kernel.org/r/20200120223201.241390-4-ebiggers@kernel.org Reviewed-by: Daniel Rosenberg Signed-off-by: Eric Biggers

fscrypt: derive dirhash key for casefolded directories

2020-01-22T22:49:55+00:00

When we allow indexed directories to use both encryption and casefolding, for the dirhash we can't just hash the ciphertext filenames that are stored on-disk (as is done currently) because the dirhash must be case insensitive, but the stored names are case-preserving. Nor can we hash the plaintext names with an unkeyed hash (or a hash keyed with a value stored on-disk like ext4's s_hash_seed), since that would leak information about the names that encryption is meant to protect. Instead, if we can accept a dirhash that's only computable when the fscrypt key is available, we can hash the plaintext names with a keyed hash using a secret key derived from the directory's fscrypt master key. We'll use SipHash-2-4 for this purpose. Prepare for this by deriving a SipHash key for each casefolded encrypted directory. Make sure to handle deriving the key not only when setting up the directory's fscrypt_info, but also in the case where the casefold flag is enabled after the fscrypt_info was already set up. (We could just always derive the key regardless of casefolding, but that would introduce unnecessary overhead for people not using casefolding.) Signed-off-by: Daniel Rosenberg [EB: improved commit message, updated fscrypt.rst, squashed with change that avoids unnecessarily deriving the key, and many other cleanups] Link: https://lore.kernel.org/r/20200120223201.241390-3-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: don't allow v1 policies with casefolding

2020-01-22T22:47:15+00:00

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 [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

fscrypt: add "fscrypt_" prefix to fname_encrypt()

2020-01-22T22:45:10+00:00

fname_encrypt() is a global function, due to being used in both fname.c and hooks.c. So it should be prefixed with "fscrypt_", like all the other global functions in fs/crypto/. Link: https://lore.kernel.org/r/20200120071736.45915-1-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: don't print name of busy file when removing key

2020-01-22T22:45:08+00:00

When an encryption key can't be fully removed due to file(s) protected by it still being in-use, we shouldn't really print the path to one of these files to the kernel log, since parts of this path are likely to be encrypted on-disk, and (depending on how the system is set up) the confidentiality of this path might be lost by printing it to the log. This is a trade-off: a single file path often doesn't matter at all, especially if it's a directory; the kernel log might still be protected in some way; and I had originally hoped that any "inode(s) still busy" bugs (which are security weaknesses in their own right) would be quickly fixed and that to do so it would be super helpful to always know the file path and not have to run 'find dir -inum $inum' after the fact. But in practice, these bugs can be hard to fix (e.g. due to asynchronous process killing that is difficult to eliminate, for performance reasons), and also not tied to specific files, so knowing a file path doesn't necessarily help. So to be safe, for now let's just show the inode number, not the path. If someone really wants to know a path they can use 'find -inum'. Fixes: b1c0ec3599f4 ("fscrypt: add FS_IOC_REMOVE_ENCRYPTION_KEY ioctl") Cc: # v5.4+ Link: https://lore.kernel.org/r/20200120060732.390362-1-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: document gfp_flags for bounce page allocation

2020-01-14T20:51:12+00:00

Document that fscrypt_encrypt_pagecache_blocks() allocates the bounce page from a mempool, and document what this means for the @gfp_flags argument. Link: https://lore.kernel.org/r/20191231181026.47400-1-ebiggers@kernel.org Reviewed-by: Theodore Ts'o Signed-off-by: Eric Biggers

fscrypt: optimize fscrypt_zeroout_range()

2020-01-14T20:50:33+00:00

Currently fscrypt_zeroout_range() issues and waits on a bio for each block it writes, which makes it very slow. Optimize it to write up to 16 pages at a time instead. Also add a function comment, and improve reliability by allowing the allocations of the bio and the first ciphertext page to wait on the corresponding mempools. Link: https://lore.kernel.org/r/20191226160813.53182-1-ebiggers@kernel.org Reviewed-by: Theodore Ts'o Signed-off-by: Eric Biggers

fscrypt: remove redundant bi_status check

2019-12-31T16:33:51+00:00

submit_bio_wait() already returns bi_status translated to an errno. So the additional check of bi_status is redundant and can be removed. Link: https://lore.kernel.org/r/20191209204509.228942-1-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: Allow modular crypto algorithms

2019-12-31T16:33:51+00:00

The commit 643fa9612bf1 ("fscrypt: remove filesystem specific build config option") removed modular support for fs/crypto. This causes the Crypto API to be built-in whenever fscrypt is enabled. This makes it very difficult for me to test modular builds of the Crypto API without disabling fscrypt which is a pain. As fscrypt is still evolving and it's developing new ties with the fs layer, it's hard to build it as a module for now. However, the actual algorithms are not required until a filesystem is mounted. Therefore we can allow them to be built as modules. Signed-off-by: Herbert Xu Link: https://lore.kernel.org/r/20191227024700.7vrzuux32uyfdgum@gondor.apana.org.au Signed-off-by: Eric Biggers