76e81d6d50
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>
109 lines
2.8 KiB
C
109 lines
2.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* fscrypt_private.h
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*
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* Copyright (C) 2015, Google, Inc.
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*
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* This contains encryption key functions.
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*
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* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
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*/
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#ifndef _FSCRYPT_PRIVATE_H
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#define _FSCRYPT_PRIVATE_H
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#define __FS_HAS_ENCRYPTION 1
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#include <linux/fscrypt.h>
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#include <crypto/hash.h>
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/* Encryption parameters */
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#define FS_IV_SIZE 16
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#define FS_AES_128_ECB_KEY_SIZE 16
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#define FS_AES_128_CBC_KEY_SIZE 16
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#define FS_AES_128_CTS_KEY_SIZE 16
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#define FS_AES_256_GCM_KEY_SIZE 32
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#define FS_AES_256_CBC_KEY_SIZE 32
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#define FS_AES_256_CTS_KEY_SIZE 32
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#define FS_AES_256_XTS_KEY_SIZE 64
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#define FS_KEY_DERIVATION_NONCE_SIZE 16
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/**
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* Encryption context for inode
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*
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* Protector format:
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* 1 byte: Protector format (1 = this version)
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* 1 byte: File contents encryption mode
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* 1 byte: File names encryption mode
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* 1 byte: Flags
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* 8 bytes: Master Key descriptor
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* 16 bytes: Encryption Key derivation nonce
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*/
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struct fscrypt_context {
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u8 format;
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u8 contents_encryption_mode;
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u8 filenames_encryption_mode;
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u8 flags;
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u8 master_key_descriptor[FS_KEY_DESCRIPTOR_SIZE];
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u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
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} __packed;
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#define FS_ENCRYPTION_CONTEXT_FORMAT_V1 1
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/*
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* A pointer to this structure is stored in the file system's in-core
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* representation of an inode.
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*/
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struct fscrypt_info {
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u8 ci_data_mode;
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u8 ci_filename_mode;
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u8 ci_flags;
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struct crypto_skcipher *ci_ctfm;
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struct crypto_cipher *ci_essiv_tfm;
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u8 ci_master_key[FS_KEY_DESCRIPTOR_SIZE];
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};
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typedef enum {
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FS_DECRYPT = 0,
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FS_ENCRYPT,
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} fscrypt_direction_t;
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#define FS_CTX_REQUIRES_FREE_ENCRYPT_FL 0x00000001
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#define FS_CTX_HAS_BOUNCE_BUFFER_FL 0x00000002
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static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
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u32 filenames_mode)
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{
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if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC &&
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filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS)
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return true;
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if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS &&
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filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS)
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return true;
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return false;
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}
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/* crypto.c */
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extern struct kmem_cache *fscrypt_info_cachep;
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extern int fscrypt_initialize(unsigned int cop_flags);
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extern struct workqueue_struct *fscrypt_read_workqueue;
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extern int fscrypt_do_page_crypto(const struct inode *inode,
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fscrypt_direction_t rw, u64 lblk_num,
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struct page *src_page,
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struct page *dest_page,
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unsigned int len, unsigned int offs,
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gfp_t gfp_flags);
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extern struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
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gfp_t gfp_flags);
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/* fname.c */
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extern int fname_encrypt(struct inode *inode,
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const struct qstr *iname, struct fscrypt_str *oname);
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/* keyinfo.c */
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extern void __exit fscrypt_essiv_cleanup(void);
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#endif /* _FSCRYPT_PRIVATE_H */
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