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Add an SFTP server to the SSH server code.

Browse Source 
Unlike the traditional Unix SSH server organisation, the SFTP server
is built into the same process as all the rest of the code. sesschan.c
spots a subsystem request for "sftp", and responds to it by
instantiating an SftpServer object and swapping out its own vtable for
one that talks to it.

(I rather like the idea of an object swapping its own vtable for a
different one in the middle of its lifetime! This is one of those
tricks that would be absurdly hard to implement in a 'proper' OO
language, but when you're doing vtables by hand in C, it's no more
difficult than any other piece of ordinary pointer manipulation. As
long as the methods in both vtables expect the same physical structure
layout, it doesn't cause a problem.)

The SftpServer object doesn't deal directly with SFTP packet formats;
it implements the SFTP server logic in a more abstract way, by having
a vtable method for each SFTP request type with an appropriate
parameter list. It sends its replies by calling methods in another
vtable called SftpReplyBuilder, which in the normal case will write an
SFTP reply packet to send back to the client. So SftpServer can focus
more or less completely on the details of a particular filesystem API
- and hence, the implementation I've got lives in the unix source
directory, and works directly with file descriptors and struct stat
and the like.

(One purpose of this abstraction layer is that I may well want to
write a second dummy implementation, for test-suite purposes, with
completely controllable behaviour, and now I have a handy place to
plug it in in place of the live filesystem.)

In between sesschan's parsing of the byte stream into SFTP packets and
the SftpServer object, there's a layer in the new file sftpserver.c
which does the actual packet decoding and encoding: each request
packet is passed to that, which pulls the fields out of the request
packet and calls the appropriate method of SftpServer. It also
provides the default SftpReplyBuilder which makes the output packet.

I've moved some code out of the previous SFTP client implementation -
basic packet construction code, and in particular the BinarySink/
BinarySource marshalling fuinction for fxp_attrs - into sftpcommon.c,
so that the two directions can share as much as possible.
This commit is contained in:
Simon Tatham
2018-10-20 22:10:32 +01:00
parent 1d323d5c80
commit a081dd0a4c
16 changed files with 1473 additions and 140 deletions
Download Patch File Download Diff File Expand all files Collapse all files

214
sftp.h
View File

@ -86,6 +86,7 @@ struct fxp_attrs {
unsigned long atime;
unsigned long mtime;
};
extern const struct fxp_attrs no_attrs;
/*
* Copy between the possibly-unused permissions field in an fxp_attrs
@ -96,9 +97,9 @@ struct fxp_attrs {
((attrs).flags |= SSH_FILEXFER_ATTR_PERMISSIONS, \
(attrs).permissions = (perms)) : \
((attrs).flags &= ~SSH_FILEXFER_ATTR_PERMISSIONS))
#define GET_PERMISSIONS(attrs) \
#define GET_PERMISSIONS(attrs, defaultperms) \
((attrs).flags & SSH_FILEXFER_ATTR_PERMISSIONS ? \
(attrs).permissions : -1)
(attrs).permissions : defaultperms)
struct fxp_handle {
char *hstring;
@ -116,7 +117,47 @@ struct fxp_names {
};
struct sftp_request;
struct sftp_packet;
/*
* Packet-manipulation functions.
*/
struct sftp_packet {
char *data;
unsigned length, maxlen;
unsigned savedpos;
int type;
BinarySink_IMPLEMENTATION;
BinarySource_IMPLEMENTATION;
};
/* When sending a packet, create it with sftp_pkt_init, then add
* things to it by treating it as a BinarySink. When it's done, call
* sftp_send_prepare, and then pkt->data and pkt->length describe its
* wire format. */
struct sftp_packet *sftp_pkt_init(int pkt_type);
void sftp_send_prepare(struct sftp_packet *pkt);
/* When receiving a packet, create it with sftp_recv_prepare once you
* decode its length from the first 4 bytes of wire data. Then write
* that many bytes into pkt->data, and call sftp_recv_finish to set up
* the type code and BinarySource. */
struct sftp_packet *sftp_recv_prepare(unsigned length);
int sftp_recv_finish(struct sftp_packet *pkt);
/* Either kind of packet can be freed afterwards with sftp_pkt_free. */
void sftp_pkt_free(struct sftp_packet *pkt);
void BinarySink_put_fxp_attrs(BinarySink *bs, struct fxp_attrs attrs);
int BinarySource_get_fxp_attrs(BinarySource *src, struct fxp_attrs *attrs);
#define put_fxp_attrs(bs, attrs) \
BinarySink_put_fxp_attrs(BinarySink_UPCAST(bs), attrs)
#define get_fxp_attrs(bs, attrs) \
BinarySource_get_fxp_attrs(BinarySource_UPCAST(bs), attrs)
/*
* Error handling.
*/
const char *fxp_error(void);
int fxp_error_type(void);
@ -269,3 +310,170 @@ int xfer_upload_gotpkt(struct fxp_xfer *xfer, struct sftp_packet *pktin);
int xfer_done(struct fxp_xfer *xfer);
void xfer_set_error(struct fxp_xfer *xfer);
void xfer_cleanup(struct fxp_xfer *xfer);
/*
* Vtable for the platform-specific filesystem implementation that
* answers requests in an SFTP server.
*/
typedef struct SftpReplyBuilder SftpReplyBuilder;
struct SftpServer {
const SftpServerVtable *vt;
};
struct SftpServerVtable {
SftpServer *(*new)(const SftpServerVtable *vt);
void (*free)(SftpServer *srv);
/*
* Handle actual filesystem requests.
*
* Each of these functions replies by calling an appropiate
* sftp_reply_foo() function on the given reply packet.
*/
/* Should call fxp_reply_error or fxp_reply_simple_name */
void (*realpath)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen path);
/* Should call fxp_reply_error or fxp_reply_handle */
void (*open)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen path, unsigned flags, struct fxp_attrs attrs);
/* Should call fxp_reply_error or fxp_reply_handle */
void (*opendir)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen path);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*close)(SftpServer *srv, SftpReplyBuilder *reply, ptrlen handle);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*mkdir)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen path, struct fxp_attrs attrs);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*rmdir)(SftpServer *srv, SftpReplyBuilder *reply, ptrlen path);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*remove)(SftpServer *srv, SftpReplyBuilder *reply, ptrlen path);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*rename)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen srcpath, ptrlen dstpath);
/* Should call fxp_reply_error or fxp_reply_attrs */
void (*stat)(SftpServer *srv, SftpReplyBuilder *reply, ptrlen path,
int follow_symlinks);
/* Should call fxp_reply_error or fxp_reply_attrs */
void (*fstat)(SftpServer *srv, SftpReplyBuilder *reply, ptrlen handle);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*setstat)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen path, struct fxp_attrs attrs);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*fsetstat)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen handle, struct fxp_attrs attrs);
/* Should call fxp_reply_error or fxp_reply_data */
void (*read)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen handle, uint64 offset, unsigned length);
/* Should call fxp_reply_error or fxp_reply_ok */
void (*write)(SftpServer *srv, SftpReplyBuilder *reply,
ptrlen handle, uint64 offset, ptrlen data);
/* Should call fxp_reply_error, or fxp_reply_name_count once and
* then fxp_reply_full_name that many times */
void (*readdir)(SftpServer *srv, SftpReplyBuilder *reply, ptrlen handle,
int max_entries, int omit_longname);
};
#define sftpsrv_new(vt) \
((vt)->new(vt))
#define sftpsrv_free(srv) \
((srv)->vt->free(srv))
#define sftpsrv_realpath(srv, reply, path) \
((srv)->vt->realpath(srv, reply, path))
#define sftpsrv_open(srv, reply, path, flags, attrs) \
((srv)->vt->open(srv, reply, path, flags, attrs))
#define sftpsrv_opendir(srv, reply, path) \
((srv)->vt->opendir(srv, reply, path))
#define sftpsrv_close(srv, reply, handle) \
((srv)->vt->close(srv, reply, handle))
#define sftpsrv_mkdir(srv, reply, path, attrs) \
((srv)->vt->mkdir(srv, reply, path, attrs))
#define sftpsrv_rmdir(srv, reply, path) \
((srv)->vt->rmdir(srv, reply, path))
#define sftpsrv_remove(srv, reply, path) \
((srv)->vt->remove(srv, reply, path))
#define sftpsrv_rename(srv, reply, srcpath, dstpath) \
((srv)->vt->rename(srv, reply, srcpath, dstpath))
#define sftpsrv_stat(srv, reply, path, follow) \
((srv)->vt->stat(srv, reply, path, follow))
#define sftpsrv_fstat(srv, reply, handle) \
((srv)->vt->fstat(srv, reply, handle))
#define sftpsrv_setstat(srv, reply, path, attrs) \
((srv)->vt->setstat(srv, reply, path, attrs))
#define sftpsrv_fsetstat(srv, reply, handle, attrs) \
((srv)->vt->fsetstat(srv, reply, handle, attrs))
#define sftpsrv_read(srv, reply, handle, offset, length) \
((srv)->vt->read(srv, reply, handle, offset, length))
#define sftpsrv_write(srv, reply, handle, offset, data) \
((srv)->vt->write(srv, reply, handle, offset, data))
#define sftpsrv_readdir(srv, reply, handle, max, nolongname) \
((srv)->vt->readdir(srv, reply, handle, max, nolongname))
typedef struct SftpReplyBuilderVtable SftpReplyBuilderVtable;
struct SftpReplyBuilder {
const SftpReplyBuilderVtable *vt;
};
struct SftpReplyBuilderVtable {
void (*reply_ok)(SftpReplyBuilder *reply);
void (*reply_error)(SftpReplyBuilder *reply, unsigned code,
const char *msg);
void (*reply_simple_name)(SftpReplyBuilder *reply, ptrlen name);
void (*reply_name_count)(SftpReplyBuilder *reply, unsigned count);
void (*reply_full_name)(SftpReplyBuilder *reply, ptrlen name,
ptrlen longname, struct fxp_attrs attrs);
void (*reply_handle)(SftpReplyBuilder *reply, ptrlen handle);
void (*reply_data)(SftpReplyBuilder *reply, ptrlen data);
void (*reply_attrs)(SftpReplyBuilder *reply, struct fxp_attrs attrs);
};
#define fxp_reply_ok(reply) \
((reply)->vt->reply_ok(reply))
#define fxp_reply_error(reply, code, msg) \
((reply)->vt->reply_error(reply, code, msg))
#define fxp_reply_simple_name(reply, name) \
((reply)->vt->reply_simple_name(reply, name))
#define fxp_reply_name_count(reply, count) \
((reply)->vt->reply_name_count(reply, count))
#define fxp_reply_full_name(reply, name, longname, attrs) \
((reply)->vt->reply_full_name(reply, name, longname, attrs))
#define fxp_reply_handle(reply, handle) \
((reply)->vt->reply_handle(reply, handle))
#define fxp_reply_data(reply, data) \
((reply)->vt->reply_data(reply, data))
#define fxp_reply_attrs(reply, attrs) \
((reply)->vt->reply_attrs(reply, attrs))
/*
* The usual implementation of an SftpReplyBuilder, containing a
* 'struct sftp_packet' which is assumed to be already initialised
* before one of the above request methods is called.
*/
extern const struct SftpReplyBuilderVtable DefaultSftpReplyBuilder_vt;
typedef struct DefaultSftpReplyBuilder DefaultSftpReplyBuilder;
struct DefaultSftpReplyBuilder {
SftpReplyBuilder rb;
struct sftp_packet *pkt;
};
/*
* The top-level function that handles an SFTP request, given an
* implementation of the above SftpServer abstraction to do the actual
* filesystem work. It handles all the marshalling and unmarshalling
* of packets, and the copying of request ids into the responses.
*/
struct sftp_packet *sftp_handle_request(
SftpServer *srv, struct sftp_packet *request);