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Fixed serious bug related to multiple cleartext signatures.

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This commit is contained in:
Werner Koch 2000-10-13 15:03:48 +00:00
parent cfdb80a759
commit 2092d0f6ed
8 changed files with 192 additions and 47 deletions
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4
NEWS
View File

@ -3,7 +3,9 @@
be used to verify signatures against a list of trusted keys.
* Rijndael (AES) is now supported and listed as first preference.
* Fixed a serious bug which could lead to false signature verification
results when more than one clearsigned signatures are in one file.
Noteworthy changes in version 1.0.3 (2000-09-18)
------------------------------------------------

11
g10/ChangeLog
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@ -1,5 +1,16 @@
2000-10-13 Werner Koch <wk@gnupg.org>
* mainproc.c (add_gpg_control): New.
(do_proc_packets): use it.
(proc_plaintext): Changed logic to detect clearsigns.
(proc_tree): Check the cleartext sig with some new code.
* packet.h: New packet PKT_GPG_CONTROL.
* parse-packet.c (parse_gpg_control): New.
* misc.c (get_session_marker): New.
* armor.c (armor_filter): Replaced the faked 1-pass packet by the
new control packet.
* keyedit.c (keyedit_menu): Allow batchmode with a command_fd.
* status.c (my_read): New.
(do_get_from_fd): use it.

60
g10/armor.c
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@ -502,7 +502,7 @@ fake_packet( armor_filter_context_t *afx, IOBUF a,
/* the buffer is always allocated with enough space to append
* the removed [CR], LF and a Nul
* The reason for this complicated procedure is to keep at least
* the original tupe of lineending - handling of the removed
* the original type of lineending - handling of the removed
* trailing spaces seems to be impossible in our method
* of faking a packet; either we have to use a temporary file
* or calculate the hash here in this module and somehow find
@ -815,7 +815,9 @@ armor_filter( void *opaque, int control,
*ret_len = n;
}
else if( control == IOBUFCTRL_UNDERFLOW ) {
if( size < 15+(4*15) ) /* need space for up to 4 onepass_sigs */
/* We need some space for the faked packet. The minmum required
* size is ~18 + length of the session marker */
if( size < 50 )
BUG(); /* supplied buffer too short */
if( afx->faked )
@ -831,7 +833,14 @@ armor_filter( void *opaque, int control,
rc = -1;
}
else if( afx->faked ) {
unsigned hashes = afx->hashes;
unsigned int hashes = afx->hashes;
const byte *sesmark;
size_t sesmarklen;
sesmark = get_session_marker( &sesmarklen );
if ( sesmarklen > 20 )
BUG();
/* the buffer is at least 15+n*15 bytes long, so it
* is easy to construct the packets */
@ -842,36 +851,21 @@ armor_filter( void *opaque, int control,
afx->pgp2mode = 1;
}
n=0;
do {
/* first some onepass signature packets */
buf[n++] = 0x90; /* old format, type 4, 1 length byte */
buf[n++] = 13; /* length */
buf[n++] = 3; /* version */
buf[n++] = afx->not_dash_escaped? 0:1; /* sigclass */
if( hashes & 1 ) {
hashes &= ~1;
buf[n++] = DIGEST_ALGO_RMD160;
}
else if( hashes & 2 ) {
hashes &= ~2;
buf[n++] = DIGEST_ALGO_SHA1;
}
else if( hashes & 4 ) {
hashes &= ~4;
buf[n++] = DIGEST_ALGO_MD5;
}
else if( hashes & 8 ) {
hashes &= ~8;
buf[n++] = DIGEST_ALGO_TIGER;
}
else
buf[n++] = 0; /* (don't know) */
buf[n++] = 0; /* public key algo (don't know) */
memset(buf+n, 0, 8); /* don't know the keyid */
n += 8;
buf[n++] = !hashes; /* last one */
} while( hashes );
/* first a gpg control packet */
buf[n++] = 0xff; /* new format, type 63, 1 length byte */
n++; /* see below */
memcpy(buf+n, sesmark, sesmarklen ); n+= sesmarklen;
buf[n++] = 1; /* control type */
buf[n++] = afx->not_dash_escaped? 0:1; /* sigclass */
if( hashes & 1 )
buf[n++] = DIGEST_ALGO_RMD160;
if( hashes & 2 )
buf[n++] = DIGEST_ALGO_SHA1;
if( hashes & 4 )
buf[n++] = DIGEST_ALGO_MD5;
if( hashes & 8 )
buf[n++] = DIGEST_ALGO_TIGER;
buf[1] = n - 2;
/* followed by a plaintext packet */
buf[n++] = 0xaf; /* old packet format, type 11, var length */

1
g10/main.h
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@ -60,6 +60,7 @@ u16 checksum( byte *p, unsigned n );
u16 checksum_mpi( MPI a );
u16 checksum_mpi_counted_nbits( MPI a );
u32 buffer_to_u32( const byte *buffer );
const byte *get_session_marker( size_t *rlen );
/*-- helptext.c --*/
void display_online_help( const char *keyword );

61
g10/mainproc.c
View File

@ -119,6 +119,24 @@ add_onepass_sig( CTX c, PACKET *pkt )
}
static int
add_gpg_control( CTX c, PACKET *pkt )
{
if ( pkt->pkt.gpg_control->control == 1 ) {
/* New clear text signature.
* Process the last one and reset everything */
release_list(c);
}
if( c->list ) /* add another packet */
add_kbnode( c->list, new_kbnode( pkt ));
else /* insert the first one */
c->list = new_kbnode( pkt );
return 1;
}
static int
add_user_id( CTX c, PACKET *pkt )
@ -412,20 +430,23 @@ proc_plaintext( CTX c, PACKET *pkt )
}
if( n->pkt->pkt.onepass_sig->sig_class != 0x01 )
only_md5 = 0;
/* Check whether this is a cleartext signature. We assume that
* we have one if the sig_class is 1 and the keyid is 0, that
* are the faked packets produced by armor.c. There is a
* possibility that this fails, but there is no other easy way
* to do it. (We could use a special packet type to indicate
* this, but this may also be faked - it simply can't be verified
* and is _no_ security issue)
*/
if( n->pkt->pkt.onepass_sig->sig_class == 0x01
&& !n->pkt->pkt.onepass_sig->keyid[0]
&& !n->pkt->pkt.onepass_sig->keyid[1] )
clearsig = 1;
}
else if( n->pkt->pkttype == PKT_GPG_CONTROL
&& n->pkt->pkt.gpg_control->control == 1 ) {
size_t datalen = n->pkt->pkt.gpg_control->datalen;
const byte *data = n->pkt->pkt.gpg_control->data;
/* check that we have at least the sigclass and one hash */
if ( datalen < 2 )
log_fatal("invalid control packet of type 1\n");
/* Note that we don't set the clearsig flag for not-dash-escaped
* documents */
clearsig = (*data == 0x01);
for( data++, datalen--; datalen; datalen--, data++ )
md_enable( c->mfx.md, *data );
any = 1;
break; /* no pass signature pakets are expected */
}
}
if( !any && !opt.skip_verify ) {
@ -993,6 +1014,7 @@ do_proc_packets( CTX c, IOBUF a )
case PKT_PLAINTEXT: proc_plaintext( c, pkt ); break;
case PKT_COMPRESSED: proc_compressed( c, pkt ); break;
case PKT_ONEPASS_SIG: newpkt = add_onepass_sig( c, pkt ); break;
case PKT_GPG_CONTROL: newpkt = add_gpg_control(c, pkt); break;
default: newpkt = 0; break;
}
}
@ -1011,6 +1033,7 @@ do_proc_packets( CTX c, IOBUF a )
case PKT_PLAINTEXT: proc_plaintext( c, pkt ); break;
case PKT_COMPRESSED: proc_compressed( c, pkt ); break;
case PKT_ONEPASS_SIG: newpkt = add_onepass_sig( c, pkt ); break;
case PKT_GPG_CONTROL: newpkt = add_gpg_control(c, pkt); break;
default: newpkt = 0; break;
}
}
@ -1035,6 +1058,7 @@ do_proc_packets( CTX c, IOBUF a )
case PKT_PLAINTEXT: proc_plaintext( c, pkt ); break;
case PKT_COMPRESSED: proc_compressed( c, pkt ); break;
case PKT_ONEPASS_SIG: newpkt = add_onepass_sig( c, pkt ); break;
case PKT_GPG_CONTROL: newpkt = add_gpg_control(c, pkt); break;
case PKT_RING_TRUST: newpkt = add_ring_trust( c, pkt ); break;
default: newpkt = 0; break;
}
@ -1228,6 +1252,17 @@ proc_tree( CTX c, KBNODE node )
for( n1 = node; (n1 = find_next_kbnode(n1, PKT_SIGNATURE )); )
check_sig_and_print( c, n1 );
}
else if( node->pkt->pkttype == PKT_GPG_CONTROL
&& node->pkt->pkt.gpg_control->control == 1 ) {
/* clear text signed message */
if( !c->have_data ) {
log_error("cleartext signature without data\n" );
return;
}
for( n1 = node; (n1 = find_next_kbnode(n1, PKT_SIGNATURE )); )
check_sig_and_print( c, n1 );
}
else if( node->pkt->pkttype == PKT_SIGNATURE ) {
PKT_signature *sig = node->pkt->pkt.signature;

27
g10/misc.c
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@ -22,6 +22,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#if defined(__linux__) && defined(__alpha__) && __GLIBC__ < 2
#include <asm/sysinfo.h>
@ -244,6 +245,32 @@ print_digest_algo_note( int algo )
}
/* Return a string which is used as a kind of process ID */
const byte *
get_session_marker( size_t *rlen )
{
static byte marker[SIZEOF_UNSIGNED_LONG*2];
static int initialized;
if ( !initialized ) {
volatile ulong aa, bb; /* we really want the unitialized value */
ulong a, b;
initialized = 1;
/* also this marker is guessable it is not easy to use this
* for a faked control packet because an attacker does not
* have enough control about the time the verification does
* take place. Of course, we can add just more random but
* than we need the random generator even for verification
* tasks - which does not make sense. */
a = aa ^ (ulong)getpid();
b = bb ^ (ulong)time(NULL);
memcpy( marker, &a, SIZEOF_UNSIGNED_LONG );
memcpy( marker+SIZEOF_UNSIGNED_LONG, &b, SIZEOF_UNSIGNED_LONG );
}
*rlen = sizeof(marker);
return marker;
}

7
g10/packet.h
View File

@ -50,6 +50,7 @@ typedef enum {
PKT_ENCRYPTED_MDC =18, /* integrity protected encrypted data */
PKT_MDC =19, /* manipulaion detection code packet */
PKT_COMMENT =61, /* new comment packet (private) */
PKT_GPG_CONTROL =63 /* internal control packet */
} pkttype_t;
typedef struct packet_struct PACKET;
@ -194,6 +195,11 @@ typedef struct {
char name[1];
} PKT_plaintext;
typedef struct {
int control;
size_t datalen;
char data[1];
} PKT_gpg_control;
/* combine all packets into a union */
struct packet_struct {
@ -213,6 +219,7 @@ struct packet_struct {
PKT_mdc *mdc; /* PKT_MDC */
PKT_ring_trust *ring_trust; /* PKT_RING_TRUST */
PKT_plaintext *plaintext; /* PKT_PLAINTEXT */
PKT_gpg_control *gpg_control; /* PKT_GPG_CONTROL */
} pkt;
};

68
g10/parse-packet.c
View File

@ -75,6 +75,8 @@ static int parse_encrypted( IOBUF inp, int pkttype, unsigned long pktlen,
PACKET *packet, int new_ctb);
static int parse_mdc( IOBUF inp, int pkttype, unsigned long pktlen,
PACKET *packet, int new_ctb);
static int parse_gpg_control( IOBUF inp, int pkttype, unsigned long pktlen,
PACKET *packet );
static unsigned short
read_16(IOBUF inp)
@ -446,6 +448,9 @@ parse( IOBUF inp, PACKET *pkt, int reqtype, ulong *retpos,
case PKT_MDC:
rc = parse_mdc(inp, pkttype, pktlen, pkt, new_ctb );
break;
case PKT_GPG_CONTROL:
rc = parse_gpg_control(inp, pkttype, pktlen, pkt );
break;
default:
skip_packet(inp, pkttype, pktlen);
break;
@ -1783,3 +1788,66 @@ parse_mdc( IOBUF inp, int pkttype, unsigned long pktlen,
return 0;
}
/*
* This packet is internally generated by PGG (by armor.c) to
* transfer some information to the lower layer. To make sure that
* this packet is really a GPG faked one and not one comming from outside,
* we first check that tehre is a unique tag in it.
* The format of such a control packet is:
* n byte session marker
* 1 byte control type: 1 = Clearsign hash info
* m byte control data
*/
static int
parse_gpg_control( IOBUF inp,
int pkttype, unsigned long pktlen, PACKET *packet )
{
byte *p;
const byte *sesmark;
size_t sesmarklen;
int i;
if ( list_mode )
printf(":packet 63: length %lu ", pktlen);
sesmark = get_session_marker ( &sesmarklen );
if ( pktlen < sesmarklen+1 ) /* 1 is for the control bytes */
goto skipit;
for( i=0; i < sesmarklen; i++, pktlen-- ) {
if ( sesmark[i] != iobuf_get_noeof(inp) )
goto skipit;
}
if ( list_mode )
puts ("- gpg control packet");
packet->pkt.gpg_control = m_alloc(sizeof *packet->pkt.gpg_control
+ pktlen - 1);
packet->pkt.gpg_control->control = iobuf_get_noeof(inp); pktlen--;
packet->pkt.gpg_control->datalen = pktlen;
p = packet->pkt.gpg_control->data;
for( ; pktlen; pktlen--, p++ )
*p = iobuf_get_noeof(inp);
return 0;
skipit:
if ( list_mode ) {
int c, i=0 ;
printf("- private (rest length %lu)\n", pktlen);
if( iobuf_in_block_mode(inp) ) {
while( (c=iobuf_get(inp)) != -1 )
dump_hex_line(c, &i);
}
else {
for( ; pktlen; pktlen-- )
dump_hex_line(iobuf_get(inp), &i);
}
putchar('\n');
}
skip_rest(inp,pktlen);
return G10ERR_INVALID_PACKET;
}