Re: [PATCH 04/12] lib/base64: RFC4648-compliant base64 encoding

Himanshu Madhani
2021-11-15T15:22:04Z

On 11/12/21 06:59, Hannes Reinecke wrote:
> Add RFC4648-compliant base64 encoding and decoding routines, based on
> the base64url encoding in fs/crypto/fname.c.
>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
> include/linux/base64.h | 16 +++++++
> lib/Makefile | 2 +-
> lib/base64.c | 103 +++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 120 insertions(+), 1 deletion(-)
> create mode 100644 include/linux/base64.h
> create mode 100644 lib/base64.c
>
> diff --git a/include/linux/base64.h b/include/linux/base64.h
> new file mode 100644
> index 000000000000..660d4cb1ef31
> --- /dev/null
> +++ b/include/linux/base64.h
> @@ -0,0 +1,16 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * base64 encoding, lifted from fs/crypto/fname.c.
> + */
> +
> +#ifndef _LINUX_BASE64_H
> +#define _LINUX_BASE64_H
> +
> +#include <linux/types.h>
> +
> +#define BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
> +
> +int base64_encode(const u8 *src, int len, char *dst);
> +int base64_decode(const char *src, int len, u8 *dst);
> +
> +#endif /* _LINUX_BASE64_H */
> diff --git a/lib/Makefile b/lib/Makefile
> index 364c23f15578..ddc5cb4c6eb8 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -46,7 +46,7 @@ obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \
> bust_spinlocks.o kasprintf.o bitmap.o scatterlist.o \
> list_sort.o uuid.o iov_iter.o clz_ctz.o \
> bsearch.o find_bit.o llist.o memweight.o kfifo.o \
> - percpu-refcount.o rhashtable.o \
> + percpu-refcount.o rhashtable.o base64.o \
> once.o refcount.o usercopy.o errseq.o bucket_locks.o \
> generic-radix-tree.o
> obj-$(CONFIG_STRING_SELFTEST) += test_string.o
> diff --git a/lib/base64.c b/lib/base64.c
> new file mode 100644
> index 000000000000..60d46157da85
> --- /dev/null
> +++ b/lib/base64.c
> @@ -0,0 +1,103 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * base64.c - RFC4648-compliant base64 encoding
> + *
> + * Copyright (c) 2020 Hannes Reinecke, SUSE
> + *
> + * Based on the base64url routines from fs/crypto/fname.c
> + * (which are using the URL-safe base64 encoding),
> + * modified to use the standard coding table from RFC4648 section 4.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +#include <linux/export.h>
> +#include <linux/string.h>
> +#include <linux/base64.h>
> +
> +static const char base64_table[65] =
> + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
> +
> +/**
> + * base64_encode() - base64-encode some binary data
> + * @src: the binary data to encode
> + * @srclen: the length of @src in bytes
> + * @dst: (output) the base64-encoded string. Not NUL-terminated.
> + *
> + * Encodes data using base64 encoding, i.e. the "Base 64 Encoding" specified
> + * by RFC 4648, including the '='-padding.
> + *
> + * Return: the length of the resulting base64url-encoded string in bytes.
> + */
> +int base64_encode(const u8 *src, int srclen, char *dst)
> +{
> + u32 ac = 0;
> + int bits = 0;
> + int i;
> + char *cp = dst;
> +
> + for (i = 0; i < srclen; i++) {
> + ac = (ac << 8) | src[i];
> + bits += 8;
> + do {
> + bits -= 6;
> + *cp++ = base64_table[(ac >> bits) & 0x3f];
> + } while (bits >= 6);
> + }
> + if (bits) {
> + *cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
> + bits -= 6;
> + }
> + while (bits < 0) {
> + *cp++ = '=';
> + bits += 2;
> + }
> + return cp - dst;
> +}
> +EXPORT_SYMBOL_GPL(base64_encode);
> +
> +/**
> + * base64_decode() - base64-decode a string
> + * @src: the string to decode. Doesn't need to be NUL-terminated.
> + * @srclen: the length of @src in bytes
> + * @dst: (output) the decoded binary data
> + *
> + * Decodes a string using base64url encoding, i.e. the "Base 64 Encoding"
> + * specified by RFC 4648, including the '='-padding.
> + *
> + * This implementation hasn't been optimized for performance.
> + *
> + * Return: the length of the resulting decoded binary data in bytes,
> + * or -1 if the string isn't a valid base64 string.
> + */
> +int base64_decode(const char *src, int srclen, u8 *dst)
> +{
> + u32 ac = 0;
> + int bits = 0;
> + int i;
> + u8 *bp = dst;
> +
> + for (i = 0; i < srclen; i++) {
> + const char *p = strchr(base64_table, src[i]);
> +
> + if (src[i] == '=') {
> + ac = (ac << 6);
> + bits += 6;
> + if (bits >= 8)
> + bits -= 8;
> + continue;
> + }
> + if (p == NULL || src[i] == 0)
> + return -1;
> + ac = (ac << 6) | (p - base64_table);
> + bits += 6;
> + if (bits >= 8) {
> + bits -= 8;
> + *bp++ = (u8)(ac >> bits);
> + }
> + }
> + if (ac & ((1 << bits) - 1))
> + return -1;
> + return bp - dst;
> +}
> +EXPORT_SYMBOL_GPL(base64_decode);
>

Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>

--
Himanshu Madhani Oracle Linux Engineering