[PATCH 1/9] lib/base64: RFC4648-compliant base64 encoding

Hannes Reinecke
2022-05-27T08:05:43Z

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>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
---
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 6b9ffc1bd1ee..81a8c8230148 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..b736a7a431c5
--- /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 base64-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 base64 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);
--
2.29.2