[PATCH v4 4/4] ceph: replace base64url by the encoding used for mailbox names

[Luís Henriques]

The base64url encoding includes the '_' character, which may cause problems
in snapshot names (if the name starts with '_').  Thus, use the base64
encoding defined for IMAP mailbox names (RFC 3501), which uses '+' and ','
instead of '-' and '_'.

Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
---
 fs/ceph/crypto.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++--
 fs/ceph/crypto.h |  3 +++
 fs/ceph/dir.c    |  2 +-
 fs/ceph/inode.c  |  2 +-
 4 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/fs/ceph/crypto.c b/fs/ceph/crypto.c
index 1fa9dd634a6f..1adf97b00a4f 100644
--- a/fs/ceph/crypto.c
+++ b/fs/ceph/crypto.c
@@ -1,4 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
+/*
+ * The base64 encode/decode code was copied from fscrypt:
+ * Copyright (C) 2015, Google, Inc.
+ * Copyright (C) 2015, Motorola Mobility
+ * Written by Uday Savagaonkar, 2014.
+ * Modified by Jaegeuk Kim, 2015.
+ */
 #include <linux/ceph/ceph_debug.h>
 #include <linux/xattr.h>
 #include <linux/fscrypt.h>
@@ -8,6 +15,59 @@
 #include "mds_client.h"
 #include "crypto.h"
 
+/*
+ * The base64url encoding used by fscrypt includes the '_' character, which may
+ * cause problems in snapshot names (which can not starts with '_').  Thus, we
+ * used the base64 encoding defined for IMAP mailbox names (RFC 3501) instead,
+ * which replaces '-' and '_' by '+' and ','.
+ */
+static const char base64_table[65] =
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
+
+int ceph_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];
+	return cp - dst;
+}
+
+int ceph_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 (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;
+}
+
 static int ceph_crypt_get_context(struct inode *inode, void *ctx, size_t len)
 {
 	struct ceph_inode_info *ci = ceph_inode(inode);
@@ -261,7 +321,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, struct qstr *d_name, char
 	}
 
 	/* base64 encode the encrypted name */
-	elen = fscrypt_base64url_encode(cryptbuf, len, buf);
+	elen = ceph_base64_encode(cryptbuf, len, buf);
 	dout("base64-encoded ciphertext name = %.*s\n", elen, buf);
 
 	/* To understand the 240 limit, see CEPH_NOHASH_NAME_MAX comments */
@@ -367,7 +427,7 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
 			tname = &_tname;
 		}
 
-		declen = fscrypt_base64url_decode(name, name_len, tname->name);
+		declen = ceph_base64_decode(name, name_len, tname->name);
 		if (declen <= 0) {
 			ret = -EIO;
 			goto out;
diff --git a/fs/ceph/crypto.h b/fs/ceph/crypto.h
index 0e10f934af5c..63fb230fcb41 100644
--- a/fs/ceph/crypto.h
+++ b/fs/ceph/crypto.h
@@ -89,6 +89,9 @@ static inline u32 ceph_fscrypt_auth_len(struct ceph_fscrypt_auth *fa)
  */
 #define CEPH_NOHASH_NAME_MAX (180 - SHA256_DIGEST_SIZE)
 
+int ceph_base64_encode(const u8 *src, int srclen, char *dst);
+int ceph_base64_decode(const char *src, int srclen, u8 *dst);
+
 void ceph_fscrypt_set_ops(struct super_block *sb);
 
 void ceph_fscrypt_free_dummy_policy(struct ceph_fs_client *fsc);
diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 5ccf6453f02f..f48f1ff20927 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -966,7 +966,7 @@ static int prep_encrypted_symlink_target(struct ceph_mds_request *req, const cha
 		goto out;
 	}
 
-	len = fscrypt_base64url_encode(osd_link.name, osd_link.len, req->r_path2);
+	len = ceph_base64_encode(osd_link.name, osd_link.len, req->r_path2);
 	req->r_path2[len] = '\0';
 out:
 	fscrypt_fname_free_buffer(&osd_link);
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 8e97efa2b1a7..1df2eab767ef 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -876,7 +876,7 @@ static int decode_encrypted_symlink(const char *encsym, int enclen, u8 **decsym)
 	if (!sym)
 		return -ENOMEM;
 
-	declen = fscrypt_base64url_decode(encsym, enclen, sym);
+	declen = ceph_base64_decode(encsym, enclen, sym);
 	if (declen < 0) {
 		pr_err("%s: can't decode symlink (%d). Content: %.*s\n",
 		       __func__, declen, enclen, encsym);