fscrypt: calculate NUL-padding length in one place only
Currently, when encrypting a filename (either a real filename or a symlink target) we calculate the amount of NUL-padding twice: once before encryption and once during encryption in fname_encrypt(). It is needed before encryption to allocate the needed buffer size as well as calculate the size the symlink target will take up on-disk before creating the symlink inode. Calculating the size during encryption as well is redundant. Remove this redundancy by always calculating the exact size beforehand, and making fname_encrypt() just add as much NUL padding as is needed to fill the output buffer. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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0eaab5b106
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@ -30,39 +30,29 @@ static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
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/**
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* fname_encrypt() - encrypt a filename
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*
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* The caller must have allocated sufficient memory for the @oname string.
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* The output buffer must be at least as large as the input buffer.
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* Any extra space is filled with NUL padding before encryption.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fname_encrypt(struct inode *inode,
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const struct qstr *iname, struct fscrypt_str *oname)
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int fname_encrypt(struct inode *inode, const struct qstr *iname,
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u8 *out, unsigned int olen)
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{
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struct skcipher_request *req = NULL;
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DECLARE_CRYPTO_WAIT(wait);
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struct fscrypt_info *ci = inode->i_crypt_info;
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struct crypto_skcipher *tfm = ci->ci_ctfm;
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struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
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int res = 0;
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char iv[FS_CRYPTO_BLOCK_SIZE];
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struct scatterlist sg;
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int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
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unsigned int lim;
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unsigned int cryptlen;
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lim = inode->i_sb->s_cop->max_namelen(inode);
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if (iname->len <= 0 || iname->len > lim)
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return -EIO;
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/*
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* Copy the filename to the output buffer for encrypting in-place and
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* pad it with the needed number of NUL bytes.
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*/
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if (WARN_ON(oname->len < iname->len))
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if (WARN_ON(olen < iname->len))
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return -ENOBUFS;
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cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
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cryptlen = round_up(cryptlen, padding);
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cryptlen = min3(cryptlen, lim, oname->len);
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memcpy(oname->name, iname->name, iname->len);
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memset(oname->name + iname->len, 0, cryptlen - iname->len);
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memcpy(out, iname->name, iname->len);
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memset(out + iname->len, 0, olen - iname->len);
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/* Initialize the IV */
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memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
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@ -77,8 +67,8 @@ int fname_encrypt(struct inode *inode,
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skcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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crypto_req_done, &wait);
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sg_init_one(&sg, oname->name, cryptlen);
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skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);
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sg_init_one(&sg, out, olen);
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skcipher_request_set_crypt(req, &sg, &sg, olen, iv);
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/* Do the encryption */
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res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
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@ -89,7 +79,6 @@ int fname_encrypt(struct inode *inode,
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return res;
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}
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oname->len = cryptlen;
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return 0;
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}
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@ -354,11 +343,21 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
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return ret;
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if (dir->i_crypt_info) {
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ret = fscrypt_fname_alloc_buffer(dir, iname->len,
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&fname->crypto_buf);
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if (ret)
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return ret;
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ret = fname_encrypt(dir, iname, &fname->crypto_buf);
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unsigned int max_len = dir->i_sb->s_cop->max_namelen(dir);
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if (iname->len > max_len)
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return -ENAMETOOLONG;
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fname->crypto_buf.len =
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min(fscrypt_fname_encrypted_size(dir, iname->len),
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max_len);
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fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
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GFP_NOFS);
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if (!fname->crypto_buf.name)
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return -ENOMEM;
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ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
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fname->crypto_buf.len);
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if (ret)
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goto errout;
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fname->disk_name.name = fname->crypto_buf.name;
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@ -410,7 +409,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
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return 0;
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errout:
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fscrypt_fname_free_buffer(&fname->crypto_buf);
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kfree(fname->crypto_buf.name);
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return ret;
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}
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EXPORT_SYMBOL(fscrypt_setup_filename);
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@ -108,8 +108,8 @@ 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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extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
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u8 *out, unsigned int olen);
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/* keyinfo.c */
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extern void __exit fscrypt_essiv_cleanup(void);
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@ -161,7 +161,6 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
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struct qstr iname = { .name = target, .len = len };
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struct fscrypt_symlink_data *sd;
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unsigned int ciphertext_len;
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struct fscrypt_str oname;
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err = fscrypt_require_key(inode);
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if (err)
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@ -178,16 +177,12 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
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ciphertext_len = disk_link->len - sizeof(*sd);
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sd->len = cpu_to_le16(ciphertext_len);
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oname.name = sd->encrypted_path;
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oname.len = ciphertext_len;
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err = fname_encrypt(inode, &iname, &oname);
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err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
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if (err) {
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if (!disk_link->name)
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kfree(sd);
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return err;
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}
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BUG_ON(oname.len != ciphertext_len);
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/*
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* Null-terminating the ciphertext doesn't make sense, but we still
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* count the null terminator in the length, so we might as well
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