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#include <assert.h>
#include <errno.h>
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <utility>
#include <vector>
uid_t parse_user( const char *user ) {
char *end;
unsigned long tmp;
tmp = strtoul( user, &end, 10 );
if ( end != user && ! *end ) {
return tmp;
} else {
struct passwd *pw = getpwnam( user );
assert( pw );
return pw->pw_uid;
};
}
gid_t parse_group( const char *group ) {
char *end;
unsigned long tmp;
tmp = strtoul( group, &end, 10 );
if ( end != group && ! *end ) {
return tmp;
} else {
struct group *gr = getgrnam( group );
assert( gr );
return gr->gr_gid;
};
}
class permission {
uid_t min_uid, max_uid;
gid_t min_gid, max_gid;
public:
permission( std::pair< uid_t, uid_t > uids, std::pair< gid_t, gid_t > gids )
: min_uid( uids.first )
, max_uid( uids.second )
, min_gid( gids.first )
, max_gid( gids.second )
{
}
const bool allows( uid_t uid, gid_t gid ) {
return uid >= min_uid && uid <= max_uid && gid >= min_gid && gid <= max_gid;
}
};
template< typename thing > std::pair< thing, thing > parse_pair( const char *line, thing (*parse_one)( const char *part ) ) {
std::pair< thing, thing > ret( 0, -1 );
size_t part_len = strlen( line );
assert( part_len > 0 );
char part[part_len + 1];
strncpy( part, line, part_len );
part[part_len] = 0;
size_t comma = strcspn( line, "," );
if ( comma == part_len ) {
thing it = parse_one( part );
ret.first = it;
ret.second = it;
} else {
size_t first_len = comma;
size_t second_len = part_len - comma - 1;
char first[first_len + 1];
strncpy( first, part, first_len );
first[first_len] = 0;
char second[second_len + 1];
strncpy( second, part + comma + 1, second_len );
second[second_len] = 0;
if ( first_len )
ret.first = parse_one( first );
if ( second_len )
ret.second = parse_one( second );
};
return ret;
}
permission parse_line( const char *line ) {
size_t line_len = strcspn( line, "\n" );
assert( line_len > 0 );
size_t user_len = strcspn( line, ":" );
assert( user_len != line_len );
size_t group_len = line_len - user_len - 1;
char user[user_len + 1];
strncpy( user, line, user_len );
user[user_len] = 0;
char group[group_len + 1];
strncpy( group, line + user_len + 1, group_len );
group[group_len] = 0;
auto uid_part = parse_pair< uid_t >( user, parse_user );
auto gid_part = parse_pair< gid_t >( group, parse_group );
return permission( uid_part, gid_part );
}
std::vector< permission > * read_permissions( const char *file ) {
FILE *fh = fopen( file, "r" );
if ( not fh )
assert_perror( errno );
auto *ret = new std::vector< permission >( );
char *line = 0;
size_t size = 0;
for ( ; getline( &line, &size, fh ) != -1; ) {
size_t line_len = strcspn( line, "\n" );
if ( line_len ) {
ret->push_back( parse_line( line ) );
};
};
if ( line )
free( line );
return ret;
}
int main( int argc, char *argv[] ) {
if ( argc < 4 ) {
fprintf( stderr, "Usage: %s user group cmd [args..]\n", argv[0] );
return 1;
};
char *user = argv[1];
char *group = argv[2];
char *cmd = argv[3];
char **args = argv + 3;
uid_t uid;
gid_t gid;
uid = parse_user( user );
gid = parse_group( group );
// literally the only hard-coded security check
if ( not uid || not gid ) {
fprintf( stderr, "Neither uid nor gid may be zero!\n" );
_exit( 1 );
};
auto allowed = read_permissions( "/etc/insecuresuexec/permissions" );
// the configurable security checks
bool ok = false;
for ( auto i = allowed->begin( ); i != allowed->end( ); ++i ) {
ok |= i->allows( uid, gid );
if ( ok ) break;
};
if ( not ok ) {
fprintf( stderr, "The uid/gid pair %u/%u is not allowed!\n", uid, gid );
_exit( 1 );
};
if ( setgroups( 0, NULL ) != 0 )
assert_perror( errno );
if ( setregid( gid, gid ) != 0 )
assert_perror( errno );
if ( setreuid( uid, uid ) != 0 )
assert_perror( errno );
execv( cmd, args );
assert_perror( errno );
}
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