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fscrypt: calculate NUL-padding length in one place only

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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>
This commit is contained in:
Eric Biggers 2018-01-11 23:30:08 -05:00 committed by Theodore Ts'o
parent 0eaab5b106
commit 50c961de59
3 changed files with 29 additions and 35 deletions
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53
fs/crypto/fname.c
View file

@ -30,39 +30,29 @@ static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
/**
* fname_encrypt() - encrypt a filename
*
* The caller must have allocated sufficient memory for the @oname string.
* The output buffer must be at least as large as the input buffer.
* Any extra space is filled with NUL padding before encryption.
*
* Return: 0 on success, -errno on failure
*/
int fname_encrypt(struct inode *inode,
const struct qstr *iname, struct fscrypt_str *oname)
int fname_encrypt(struct inode *inode, const struct qstr *iname,
u8 *out, unsigned int olen)
{
struct skcipher_request *req = NULL;
DECLARE_CRYPTO_WAIT(wait);
struct fscrypt_info *ci = inode->i_crypt_info;
struct crypto_skcipher *tfm = ci->ci_ctfm;
struct crypto_skcipher *tfm = inode->i_crypt_info->ci_ctfm;
int res = 0;
char iv[FS_CRYPTO_BLOCK_SIZE];
struct scatterlist sg;
int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
unsigned int lim;
unsigned int cryptlen;
lim = inode->i_sb->s_cop->max_namelen(inode);
if (iname->len <= 0 || iname->len > lim)
return -EIO;
/*
* Copy the filename to the output buffer for encrypting in-place and
* pad it with the needed number of NUL bytes.
*/
if (WARN_ON(oname->len < iname->len))
if (WARN_ON(olen < iname->len))
return -ENOBUFS;
cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
cryptlen = round_up(cryptlen, padding);
cryptlen = min3(cryptlen, lim, oname->len);
memcpy(oname->name, iname->name, iname->len);
memset(oname->name + iname->len, 0, cryptlen - iname->len);
memcpy(out, iname->name, iname->len);
memset(out + iname->len, 0, olen - iname->len);
/* Initialize the IV */
memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
@ -77,8 +67,8 @@ int fname_encrypt(struct inode *inode,
skcipher_request_set_callback(req,
CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
crypto_req_done, &wait);
sg_init_one(&sg, oname->name, cryptlen);
skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);
sg_init_one(&sg, out, olen);
skcipher_request_set_crypt(req, &sg, &sg, olen, iv);
/* Do the encryption */
res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
@ -89,7 +79,6 @@ int fname_encrypt(struct inode *inode,
return res;
}
oname->len = cryptlen;
return 0;
}
@ -354,11 +343,21 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
return ret;
if (dir->i_crypt_info) {
ret = fscrypt_fname_alloc_buffer(dir, iname->len,
&fname->crypto_buf);
if (ret)
return ret;
ret = fname_encrypt(dir, iname, &fname->crypto_buf);
unsigned int max_len = dir->i_sb->s_cop->max_namelen(dir);
if (iname->len > max_len)
return -ENAMETOOLONG;
fname->crypto_buf.len =
min(fscrypt_fname_encrypted_size(dir, iname->len),
max_len);
fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
GFP_NOFS);
if (!fname->crypto_buf.name)
return -ENOMEM;
ret = fname_encrypt(dir, iname, fname->crypto_buf.name,
fname->crypto_buf.len);
if (ret)
goto errout;
fname->disk_name.name = fname->crypto_buf.name;
@ -410,7 +409,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
return 0;
errout:
fscrypt_fname_free_buffer(&fname->crypto_buf);
kfree(fname->crypto_buf.name);
return ret;
}
EXPORT_SYMBOL(fscrypt_setup_filename);

4
fs/crypto/fscrypt_private.h
View file

@ -108,8 +108,8 @@ extern struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
gfp_t gfp_flags);
/* fname.c */
extern int fname_encrypt(struct inode *inode,
const struct qstr *iname, struct fscrypt_str *oname);
extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
u8 *out, unsigned int olen);
/* keyinfo.c */
extern void __exit fscrypt_essiv_cleanup(void);

7
fs/crypto/hooks.c
View file

@ -161,7 +161,6 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
struct qstr iname = { .name = target, .len = len };
struct fscrypt_symlink_data *sd;
unsigned int ciphertext_len;
struct fscrypt_str oname;
err = fscrypt_require_key(inode);
if (err)
@ -178,16 +177,12 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
ciphertext_len = disk_link->len - sizeof(*sd);
sd->len = cpu_to_le16(ciphertext_len);
oname.name = sd->encrypted_path;
oname.len = ciphertext_len;
err = fname_encrypt(inode, &iname, &oname);
err = fname_encrypt(inode, &iname, sd->encrypted_path, ciphertext_len);
if (err) {
if (!disk_link->name)
kfree(sd);
return err;
}
BUG_ON(oname.len != ciphertext_len);
/*
* Null-terminating the ciphertext doesn't make sense, but we still
* count the null terminator in the length, so we might as well