[PATCH 04/13] lib/base64: RFC4648-compliant base64 encoding

[Hannes Reinecke <hare@suse.de>]

Add RFC4648-compliant base64 encoding and decoding routines.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 include/linux/base64.h |  16 ++++++
 lib/Makefile           |   2 +-
 lib/base64.c           | 115 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 132 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 6d765d5fb8ac..92a428aa0e5f 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..ef120cecceba
--- /dev/null
+++ b/lib/base64.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * base64.c - RFC4648-compliant base64 encoding
+ *
+ * Copyright (c) 2020 Hannes Reinecke, SUSE
+ *
+ * Based on the (slightly non-standard) base64 routines
+ * from fs/crypto/fname.c, but using the RFC-mandated
+ * coding table.
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/export.h>
+#include <linux/string.h>
+#include <linux/base64.h>
+
+static const char lookup_table[65] =
+	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+/**
+ * base64_encode() - base64-encode some bytes
+ * @src: the bytes to encode
+ * @len: number of bytes to encode
+ * @dst: (output) the base64-encoded string.  Not NUL-terminated.
+ *
+ * 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
+ */
+int base64_encode(const u8 *src, int len, char *dst)
+{
+	int i, bits = 0;
+	u32 ac = 0;
+	char *cp = dst;
+
+	for (i = 0; i < len; i++) {
+		ac = (ac << 8) | src[i];
+		bits += 8;
+		if (bits < 24)
+			continue;
+		do {
+			bits -= 6;
+			*cp++ = lookup_table[(ac >> bits) & 0x3f];
+		} while (bits);
+		ac = 0;
+	}
+	if (bits) {
+		int more = 0;
+
+		if (bits < 16)
+			more = 2;
+		ac = (ac << (2 + more));
+		bits += (2 + more);
+		do {
+			bits -= 6;
+			*cp++ = lookup_table[(ac >> bits) & 0x3f];
+		} while (bits);
+		*cp++ = '=';
+		if (more)
+			*cp++ = '=';
+	}
+
+	return cp - dst;
+}
+EXPORT_SYMBOL_GPL(base64_encode);
+
+/**
+ * base64_decode() - base64-decode some bytes
+ * @src: the base64-encoded string to decode
+ * @len: number of bytes to decode
+ * @dst: (output) the decoded bytes.
+ *
+ * Decodes the base64-encoded bytes @src according to RFC 4648.
+ *
+ * Return: number of decoded bytes
+ */
+int base64_decode(const char *src, int len, u8 *dst)
+{
+        int i, bits = 0, pad = 0;
+        u32 ac = 0;
+        size_t dst_len = 0;
+
+        for (i = 0; i < len; i++) {
+                int c, p = -1;
+
+                if (src[i] == '=') {
+                        pad++;
+                        if (i + 1 < len && src[i + 1] == '=')
+                                pad++;
+                        break;
+                }
+                for (c = 0; c < strlen(lookup_table); c++) {
+                        if (src[i] == lookup_table[c]) {
+                                p = c;
+                                break;
+                        }
+                }
+                if (p < 0)
+                        break;
+                ac = (ac << 6) | p;
+                bits += 6;
+                if (bits < 24)
+                        continue;
+                while (bits) {
+                        bits -= 8;
+                        dst[dst_len++] = (ac >> bits) & 0xff;
+                }
+                ac = 0;
+        }
+        dst_len -= pad;
+        return dst_len;
+}
+EXPORT_SYMBOL_GPL(base64_decode);
-- 
2.29.2


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