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fscrypt: clean up base64 encoding/decoding 

Some minor cleanups for the code that base64 encodes and decodes
encrypted filenames and long name digests:

- Rename "digest_{encode,decode}()" => "base64_{encode,decode}()" since
  they are used for filenames too, not just for long name digests.
- Replace 'while' loops with more conventional 'for' loops.
- Use 'u8' for binary data.  Keep 'char' for string data.
- Fully constify the lookup table (pointer was not const).
- Improve comment.

No actual change in behavior.

Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2019-07-24 11:07:58 -07:00
parent 75798f85f2
commit 1c5100a2aa
1 changed files with 17 additions and 17 deletions
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34
fs/crypto/fname.c
View File

@ -127,44 +127,45 @@ static int fname_decrypt(struct inode *inode,
return 0;
}
static const char *lookup_table =
static const char lookup_table[65] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
#define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
/**
* digest_encode() -
* base64_encode() -
*
* Encodes the input digest using characters from the set [a-zA-Z0-9_+].
* Encodes the input string using characters from the set [A-Za-z0-9+,].
* The encoded string is roughly 4/3 times the size of the input string.
*
* Return: length of the encoded string
*/
static int digest_encode(const char *src, int len, char *dst)
static int base64_encode(const u8 *src, int len, char *dst)
{
int i = 0, bits = 0, ac = 0;
int i, bits = 0, ac = 0;
char *cp = dst;
while (i < len) {
ac += (((unsigned char) src[i]) << bits);
for (i = 0; i < len; i++) {
ac += src[i] << bits;
bits += 8;
do {
*cp++ = lookup_table[ac & 0x3f];
ac >>= 6;
bits -= 6;
} while (bits >= 6);
i++;
}
if (bits)
*cp++ = lookup_table[ac & 0x3f];
return cp - dst;
}
static int digest_decode(const char *src, int len, char *dst)
static int base64_decode(const char *src, int len, u8 *dst)
{
int i = 0, bits = 0, ac = 0;
int i, bits = 0, ac = 0;
const char *p;
char *cp = dst;
u8 *cp = dst;
while (i < len) {
for (i = 0; i < len; i++) {
p = strchr(lookup_table, src[i]);
if (p == NULL || src[i] == 0)
return -2;
@ -175,7 +176,6 @@ static int digest_decode(const char *src, int len, char *dst)
ac >>= 8;
bits -= 8;
}
i++;
}
if (ac)
return -1;
@ -272,7 +272,7 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
return fname_decrypt(inode, iname, oname);
if (iname->len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE) {
oname->len = digest_encode(iname->name, iname->len,
oname->len = base64_encode(iname->name, iname->len,
oname->name);
return 0;
}
@ -287,7 +287,7 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
FSCRYPT_FNAME_DIGEST(iname->name, iname->len),
FSCRYPT_FNAME_DIGEST_SIZE);
oname->name[0] = '_';
oname->len = 1 + digest_encode((const char *)&digested_name,
oname->len = 1 + base64_encode((const u8 *)&digested_name,
sizeof(digested_name), oname->name + 1);
return 0;
}
@ -380,8 +380,8 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
if (fname->crypto_buf.name == NULL)
return -ENOMEM;
ret = digest_decode(iname->name + digested, iname->len - digested,
fname->crypto_buf.name);
ret = base64_decode(iname->name + digested, iname->len - digested,
fname->crypto_buf.name);
if (ret < 0) {
ret = -ENOENT;
goto errout;