ceph: pass fscrypt tname buffers directly

ceph_fname_to_usr() needs a temporary buffer for some operations
(currently only base64-decoding ciphertext) and it is convenient to
allow the caller to specify this buffer to avoid a heap allocation, so
it has a (nullable) `tname` argument. Until now, this argument was a
`struct fscrypt_str`; however, this is unnecessary for two reasons:

1. `tname->len` isn't used anywhere: ceph_fname_to_usr() assumes a
   buffer large enough to hold the ciphertext, and
   parse_reply_info_readdir() -- the only caller to use tname -- doesn't
   set it.
2. While the `tname` parameter is documented "may be NULL,"
   parse_reply_info_readdir() always passes it but with `tname->name`
   sometimes NULL in violation of the contract, indicating that the
   unnecessary container creates actual confusion.

Therefore, change the type to `unsigned char *` and pass the buffer
directly.

Signed-off-by: Sam Edwards <CFSworks@gmail.com>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/crypto.c

@@ -300,7 +300,7 @@ int ceph_encode_encrypted_dname(struct inode *parent, char *buf, int elen)
  *
  * Returns 0 on success or negative error code on error.
  */
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 		      struct fscrypt_str *oname, bool *is_nokey)
 {
 	struct inode *dir = fname->dir;
@@ -357,16 +357,15 @@ int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
 			ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
 			if (ret)
 				goto out_inode;
-			tname = &_tname;
+			tname = _tname.name;
 		}
 
-		declen = base64_decode(name, name_len,
+		declen = base64_decode(name, name_len, tname, false, BASE64_IMAP);
-				       tname->name, false, BASE64_IMAP);
 		if (declen <= 0) {
 			ret = -EIO;
 			goto out;
 		}
-		iname.name = tname->name;
+		iname.name = tname;
 		iname.len = declen;
 	} else {
 		iname.name = fname->ctext;

fs/ceph/crypto.h

@@ -115,7 +115,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 		fscrypt_fname_free_buffer(fname);
 }
 
-int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
+int ceph_fname_to_usr(const struct ceph_fname *fname, unsigned char *tname,
 		      struct fscrypt_str *oname, bool *is_nokey);
 int ceph_fscrypt_prepare_readdir(struct inode *dir);
 
@@ -204,7 +204,7 @@ static inline void ceph_fname_free_buffer(struct inode *parent,
 }
 
 static inline int ceph_fname_to_usr(const struct ceph_fname *fname,
-				    struct fscrypt_str *tname,
+				    unsigned char *tname,
 				    struct fscrypt_str *oname, bool *is_nokey)
 {
 	oname->name = fname->name;

fs/ceph/mds_client.c

@@ -491,11 +491,11 @@ static int parse_reply_info_readdir(void **p, void *end,
 		struct inode *inode = d_inode(req->r_dentry);
 		struct ceph_inode_info *ci = ceph_inode(inode);
 		struct ceph_mds_reply_dir_entry *rde = info->dir_entries + i;
-		struct fscrypt_str tname = FSTR_INIT(NULL, 0);
 		struct fscrypt_str oname = FSTR_INIT(NULL, 0);
 		struct ceph_fname fname;
 		u32 altname_len, _name_len;
 		u8 *altname, *_name;
+		u8 *tname = NULL;
 
 		/* dentry */
 		ceph_decode_32_safe(p, end, _name_len, bad);
@@ -543,7 +543,7 @@ static int parse_reply_info_readdir(void **p, void *end,
 			 * always be shorter, which is 3/4 of origin
 			 * string.
 			 */
-			tname.name = _name;
+			tname = _name;
 
 			/*
 			 * Set oname to _name too, and this will be
@@ -560,7 +560,7 @@ static int parse_reply_info_readdir(void **p, void *end,
 			oname.len = altname_len;
 		}
 		rde->is_nokey = false;
-		err = ceph_fname_to_usr(&fname, &tname, &oname, &rde->is_nokey);
+		err = ceph_fname_to_usr(&fname, tname, &oname, &rde->is_nokey);
 		if (err) {
 			pr_err_client(cl, "unable to decode %.*s, got %d\n",
 				      _name_len, _name, err);