secstore.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

/*
 * Various files from /sys/src/cmd/auth/secstore, just enough
 * to download a file at boot time.
 */

#include <u.h>
#include <libc.h>
#include <mp.h>
#include <libsec.h>
#include "drawterm.h"

static void*
emalloc(ulong n)
{
	return mallocz(n, 1);
}

enum{ CHK = 16};
enum{ MAXFILESIZE = 10*1024*1024 };

enum{// PW status bits
	Enabled 	= (1<<0),
	STA 		= (1<<1),	// extra SecurID step
};

static char testmess[] = "__secstore\tPAK\nC=%s\nm=0\n";

int
secdial(char *secstore)
{
	char *p, buf[80], *f[3];
	int fd, nf;

	p = secstore; /* take it from writehostowner, if set there */
	if(*p == 0)	  /* else use the authserver */
		p = "$auth";

	/* translate $auth ourselves.
	 * authaddr is something like il!host!566 or tcp!host!567.
	 * extract host, accounting for a change of format to something
	 * like il!host or tcp!host or host.
	 */
	if(strcmp(p, "$auth")==0){
		if(authserver == nil)
			return -1;
		strecpy(buf, buf+sizeof buf, authserver);
		nf = getfields(buf, f, nelem(f), 0, "!");
		switch(nf){
		default:
			return -1;
		case 1:
			p = f[0];
			break;
		case 2:
		case 3:
			p = f[1];
			break;
		}
	}
	fd = dial(netmkaddr(p, "tcp", "5356"), 0, 0, 0);
	if(fd >= 0)
		return fd;
	return -1;
}

int
havesecstore(char *addr, char *owner)
{
	int m, n, fd;
	uchar buf[500];

	n = snprint((char*)buf, sizeof buf, testmess, owner);
	hnputs(buf, 0x8000+n-2);

	fd = secdial(addr);
	if(fd < 0)
		return 0;
	if(write(fd, buf, n) != n || readn(fd, buf, 2) != 2){
		close(fd);
		return 0;
	}
	n = ((buf[0]&0x7f)<<8) + buf[1];
	if(n+1 > sizeof buf){
		werrstr("implausibly large count %d", n);
		close(fd);
		return 0;
	}
	m = readn(fd, buf, n);
	close(fd);
	if(m != n){
		if(m >= 0)
			werrstr("short read from secstore");
		return 0;
	}
	buf[n] = 0;
	if(strcmp((char*)buf, "!account expired") == 0){
		werrstr("account expired");
		return 0;
	}
	return strcmp((char*)buf, "!account exists") == 0;
}

// delimited, authenticated, encrypted connection
enum{ Maxmsg=4096 };	// messages > Maxmsg bytes are truncated
typedef struct SConn SConn;

extern SConn* newSConn(int);	// arg is open file descriptor
struct SConn{
	void *chan;
	int secretlen;
	int (*secret)(SConn*, uchar*, int);// 
	int (*read)(SConn*, uchar*, int); // <0 if error;  errmess in buffer
	int (*write)(SConn*, uchar*, int);
	void (*free)(SConn*);		// also closes file descriptor
};
// secret(s,b,dir) sets secret for digest, encrypt, using the secretlen
//		bytes in b to form keys 	for the two directions;
//	  set dir=0 in client, dir=1 in server

// error convention: write !message in-band
#define readstr secstore_readstr
static void writerr(SConn*, char*);
static int readstr(SConn*, char*);  // call with buf of size Maxmsg+1
	// returns -1 upon error, with error message in buf

typedef struct ConnState {
	uchar secret[SHA1dlen];
	ulong seqno;
	RC4state rc4;
} ConnState;

typedef struct SS{
	int fd;		// file descriptor for read/write of encrypted data
	int alg;	// if nonzero, "alg sha rc4_128"
	ConnState in, out;
} SS;

static int
SC_secret(SConn *conn, uchar *sigma, int direction)
{
	SS *ss = (SS*)(conn->chan);
	int nsigma = conn->secretlen;

	if(direction != 0){
		hmac_sha1(sigma, nsigma, (uchar*)"one", 3, ss->out.secret, nil);
		hmac_sha1(sigma, nsigma, (uchar*)"two", 3, ss->in.secret, nil);
	}else{
		hmac_sha1(sigma, nsigma, (uchar*)"two", 3, ss->out.secret, nil);
		hmac_sha1(sigma, nsigma, (uchar*)"one", 3, ss->in.secret, nil);
	}
	setupRC4state(&ss->in.rc4, ss->in.secret, 16); // restrict to 128 bits
	setupRC4state(&ss->out.rc4, ss->out.secret, 16);
	ss->alg = 1;
	return 0;
}

static void
hash(uchar secret[SHA1dlen], uchar *data, int len, int seqno, uchar d[SHA1dlen])
{
	DigestState sha;
	uchar seq[4];

	seq[0] = seqno>>24;
	seq[1] = seqno>>16;
	seq[2] = seqno>>8;
	seq[3] = seqno;
	memset(&sha, 0, sizeof sha);
	sha1(secret, SHA1dlen, nil, &sha);
	sha1(data, len, nil, &sha);
	sha1(seq, 4, d, &sha);
}

static int
verify(uchar secret[SHA1dlen], uchar *data, int len, int seqno, uchar d[SHA1dlen])
{
	DigestState sha;
	uchar seq[4];
	uchar digest[SHA1dlen];

	seq[0] = seqno>>24;
	seq[1] = seqno>>16;
	seq[2] = seqno>>8;
	seq[3] = seqno;
	memset(&sha, 0, sizeof sha);
	sha1(secret, SHA1dlen, nil, &sha);
	sha1(data, len, nil, &sha);
	sha1(seq, 4, digest, &sha);
	return memcmp(d, digest, SHA1dlen);
}

static int
SC_read(SConn *conn, uchar *buf, int n)
{
	SS *ss = (SS*)(conn->chan);
	uchar count[2], digest[SHA1dlen];
	int len, nr;

	if(read(ss->fd, count, 2) != 2 || (count[0]&0x80) == 0){
		werrstr("!SC_read invalid count");
		return -1;
	}
	len = (count[0]&0x7f)<<8 | count[1];	// SSL-style count; no pad
	if(ss->alg){
		len -= SHA1dlen;
		if(len <= 0 || readn(ss->fd, digest, SHA1dlen) != SHA1dlen){
			werrstr("!SC_read missing sha1");
			return -1;
		}
		if(len > n || readn(ss->fd, buf, len) != len){
			werrstr("!SC_read missing data");
			return -1;
		}
		rc4(&ss->in.rc4, digest, SHA1dlen);
		rc4(&ss->in.rc4, buf, len);
		if(verify(ss->in.secret, buf, len, ss->in.seqno, digest) != 0){
			werrstr("!SC_read integrity check failed");
			return -1;
		}
	}else{
		if(len <= 0 || len > n){
			werrstr("!SC_read implausible record length");
			return -1;
		}
		if( (nr = readn(ss->fd, buf, len)) != len){
			werrstr("!SC_read expected %d bytes, but got %d", len, nr);
			return -1;
		}
	}
	ss->in.seqno++;
	return len;
}

static int
SC_write(SConn *conn, uchar *buf, int n)
{
	SS *ss = (SS*)(conn->chan);
	uchar count[2], digest[SHA1dlen];
	int len;

	if(n <= 0 || n > Maxmsg+1){
		werrstr("!SC_write invalid n %d", n);
		return -1;
	}
	len = n;
	if(ss->alg)
		len += SHA1dlen;
	count[0] = 0x80 | len>>8;
	count[1] = len;
	if(write(ss->fd, count, 2) != 2){
		werrstr("!SC_write invalid count");
		return -1;
	}
	if(ss->alg){
		hash(ss->out.secret, buf, n, ss->out.seqno, digest);
		rc4(&ss->out.rc4, digest, SHA1dlen);
		rc4(&ss->out.rc4, buf, n);
		if(write(ss->fd, digest, SHA1dlen) != SHA1dlen ||
				write(ss->fd, buf, n) != n){
			werrstr("!SC_write error on send");
			return -1;
		}
	}else{
		if(write(ss->fd, buf, n) != n){
			werrstr("!SC_write error on send");
			return -1;
		}
	}
	ss->out.seqno++;
	return n;
}

static void
SC_free(SConn *conn)
{
	SS *ss = (SS*)(conn->chan);

	close(ss->fd);
	free(ss);
	free(conn);
}

SConn*
newSConn(int fd)
{
	SS *ss;
	SConn *conn;

	if(fd < 0)
		return nil;
	ss = (SS*)emalloc(sizeof(*ss));
	conn = (SConn*)emalloc(sizeof(*conn));
	ss->fd  = fd;
	ss->alg = 0;
	conn->chan = (void*)ss;
	conn->secretlen = SHA1dlen;
	conn->free = SC_free;
	conn->secret = SC_secret;
	conn->read = SC_read;
	conn->write = SC_write;
	return conn;
}

static void
writerr(SConn *conn, char *s)
{
	char buf[Maxmsg];

	snprint(buf, Maxmsg, "!%s", s);
	conn->write(conn, (uchar*)buf, strlen(buf));
}

static int
readstr(SConn *conn, char *s)
{
	int n;

	n = conn->read(conn, (uchar*)s, Maxmsg);
	if(n >= 0){
		s[n] = 0;
		if(s[0] == '!'){
			memmove(s, s+1, n);
			n = -1;
		}
	}else{
		strcpy(s, "read error");
	}
	return n;
}

static char*
getfile(SConn *conn, uchar *key, int nkey)
{
	char *buf;
	int nbuf, n, nr, len;