24.5 进程如何分辨谁在kill()自己
A: scz [email protected] 2003-10-11 19:31
至少对于Linux、FreeBSD、Solaris、AIX这四种操作系统，有一种办法。不要安装传 统sa_handler信号句柄，而是安装sa_sigaction信号句柄。细节请man sigaction并 参照头文件加强理解。下面是一个可移植演示程序。
/*
- For x86/Linux RedHat_8 2.4.18-14
- For x86/FreeBSD 4.5-RELEASE
- For SPARC/Solaris 8
- For AIX 4.3.3.0
- gcc -Wall -pipe -O3 -s -o siginfo_test siginfo_test.c */
/************************************************************************
-
* -
Head File * -
*
************************************************************************/
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <strings.h> #include <signal.h> #include <unistd.h> #include <setjmp.h> #include <sys/time.h>
/************************************************************************
-
* -
Macro * -
*
************************************************************************/
/*
- for signal handlers */ typedef void Sigfunc ( int, siginfo_t *, void * );
#define PRIVATE_SIG_ERR ((Sigfunc *)-1)
/************************************************************************
-
* -
Function Prototype * -
*
************************************************************************/
static void Atexit ( void ( * func ) ( void ) ); static void init_signal ( void ); static void init_timer ( unsigned int s ); static void on_alarm ( int signo, siginfo_t *si, void *unused ); static void on_segvbus ( int signo, siginfo_t *si, void *unused ); static void on_terminate ( int signo, siginfo_t *si, void *unused ); static Sigfunc * PrivateSignal ( int signo, Sigfunc *func ); static int Setitimer ( int which, struct itimerval *value, struct itimerval *ovalue ); static Sigfunc * Signal ( int signo, Sigfunc *func ); static void terminate ( void );
/************************************************************************
-
* -
Static Global Var * -
*
************************************************************************/
static sigjmp_buf jmpbuf; static volatile sig_atomic_t canjump = 0;
/************************************************************************/
static void Atexit ( void ( * func ) ( void ) ) { if ( atexit( func ) != 0 ) { exit( EXIT_FAILURE ); } return; } /* end of Atexit */
/*
-
初始化信号句柄 */ static void init_signal ( void ) { unsigned int i;
Atexit( terminate ); for ( i = 1; i < 9; i++ ) { Signal( i, on_terminate ); } Signal( SIGTERM, on_terminate ); Signal( SIGALRM, on_alarm ); Signal( SIGSEGV, on_segvbus ); Signal( SIGBUS , on_segvbus ); return; } /* end of init_signal */
/*
-
我们的定时器精度只支持到秒 */ static void init_timer ( unsigned int s ) { struct itimerval value;
value.it_value.tv_sec = s; value.it_value.tv_usec = 0; /*
- 只生效一次 / value.it_interval.tv_sec = 0; value.it_interval.tv_usec = 0; Setitimer( ITIMER_REAL, &value, NULL ); return; } / end of init_timer */
static void on_alarm ( int signo, siginfo_t *si, void unused ) { fprintf ( stderr, "\n" "signo = %d\n" "si = 0x%08X\n" "unused = 0x%08X\n", signo, ( unsigned int )si, ( unsigned int )unused ); if ( NULL != si ) { fprintf ( stderr, "si->si_signo = %d\n" "si->si_errno = %d\n" "si->si_code = %d\n" "si->si_pid = %u\n" "si->si_uid = %u\n" "si->si_status = %d\n" "si->si_addr = 0x%08X\n", si->si_signo, si->si_errno, si->si_code, ( unsigned int )si->si_pid, ( unsigned int )si->si_uid, ( int )si->si_status, ( unsigned int )si->si_addr ); } return; } / end of on_alarm */
static void on_segvbus ( int signo, siginfo_t *si, void unused ) { fprintf ( stderr, "\n" "signo = %d\n" "si = 0x%08X\n" "unused = 0x%08X\n", signo, ( unsigned int )si, ( unsigned int )unused ); if ( NULL != si ) { fprintf ( stderr, "si->si_signo = %d\n" "si->si_errno = %d\n" "si->si_code = %d\n" "si->si_pid = %u\n" "si->si_uid = %u\n" "si->si_status = %d\n" "si->si_addr = 0x%08X\n", si->si_signo, si->si_errno, si->si_code, ( unsigned int )si->si_pid, ( unsigned int )si->si_uid, ( int )si->si_status, ( unsigned int )si->si_addr ); } if ( 0 == canjump ) { / * unexpected signal, ignore / return; } canjump = 0; / * jump back to main, don't return / siglongjmp( jmpbuf, signo ); } / end of on_segvbus */
static void on_terminate ( int signo, siginfo_t *si, void unused ) { if ( NULL != si ) { / * 演示用，不推荐在信号句柄中使用fprintf() / fprintf ( stderr, "\n" "signo = %d\n" "si = 0x%08X\n" "unused = 0x%08X\n" "si->si_signo = %d\n" "si->si_errno = %d\n" "si->si_code = %d\n", signo, ( unsigned int )si, ( unsigned int )unused, si->si_signo, si->si_errno, si->si_code ); / * si_code为SI_USER时意味着"signal sent by another process with kill()" * * 就上四种OS而言，我所测试的FreeBSD反应与其他三种不同，kill进程时 * si_code始终为0，而FreeBSD有如下定义: * * #define SI_USER 0x10001 * * 如果不判断si_code，强行显示si_pid、si_uid，对于FreeBSD而言总是0。 * 下面出于方便演示目的，没有判断si_code。正确作法应该判断si_code， * 然后显示联合的不同成员。 / fprintf ( stderr, "si->si_pid = %u\n" "si->si_uid = %u\n" "si->si_status = %d\n" "si->si_addr = 0x%08X\n", ( unsigned int )si->si_pid, ( unsigned int )si->si_uid, ( int )si->si_status, ( unsigned int )si->si_addr ); } else { fprintf ( stderr, "\n" "signo = %d\n" "si = 0x%08X\n" "unused = 0x%08X\n", signo, ( unsigned int )si, ( unsigned int )unused ); } / * 这次我们使用atexit()函数 / exit( EXIT_SUCCESS ); } / end of on_terminate */
static Sigfunc * PrivateSignal ( int signo, Sigfunc *func ) { struct sigaction act, oact;
memset( &act, 0, sizeof( act ) );
sigemptyset( &act.sa_mask );
/*
* Invoke signal-catching function with three arguments instead of one.
*/
act.sa_flags = SA_SIGINFO;
act.sa_sigaction = func;
if ( SIGALRM == signo )
{#ifdef SA_INTERRUPT /* * SunOS 4.x / act.sa_flags |= SA_INTERRUPT; #endif } else { #ifdef SA_RESTART / * SVR4, 4.4BSD / act.sa_flags |= SA_RESTART; #endif } if ( sigaction( signo, &act, &oact ) < 0 ) { return( PRIVATE_SIG_ERR ); } return( oact.sa_sigaction ); } / end of PrivateSignal */
static int Setitimer ( int which, struct itimerval *value, struct itimerval *ovalue ) { int ret;
if ( ( ret = setitimer( which, value, ovalue ) ) < 0 )
{
perror( "setitimer error" );
exit( EXIT_FAILURE );
}
return( ret );} /* end of Setitimer */
static Sigfunc * Signal ( int signo, Sigfunc *func ) { Sigfunc *sigfunc;
if ( PRIVATE_SIG_ERR == ( sigfunc = PrivateSignal( signo, func ) ) )
{
perror( "signal error" );
exit( EXIT_FAILURE );
}
return( sigfunc );} /* end of Signal */
static void terminate ( void ) { /* * _exit( EXIT_SUCCESS ); / return; } / end of terminate */
int main ( int argc, char * argv[] ) { /* * for autovar, must be volatile */ volatile unsigned char *p;
init_signal();
p = ( unsigned char * )&p;
if ( 0 != sigsetjmp( jmpbuf, 1 ) )
{
printf
(
"p = 0x%08X\n",
( unsigned int )p
);
goto main_continue;
}
/*
* now sigsetjump() is OK
*/
canjump = 1;
while ( 1 )
{
/*
* 诱发SIGSEGV、SIGBUS
*/
*p = *p;
p++;
}main_continue:
/*
* 启动定时器
*/
init_timer( 1 );
while ( 1 )
{
/*
* 形成阻塞，降低CPU占用率
*/
getchar();
}
return( EXIT_SUCCESS );} /* end of main */
/************************************************************************/
这种技术是操作系统实现相关的。FreeBSD的si_code与头文件不相符。除了FreeBSD， 其他三种OS的si_addr如愿反映了栈底地址、si_pid/si_uid也能正确反映kill()信号 源。而Solaris会出现si为NULL的情形。下面是Linux上执行示例:
[scz@ /home/scz/src]> ./siginfo_test
signo = 11 si = 0xBFFFF6B0 unused = 0xBFFFF730 si->si_signo = 11 si->si_errno = 0 si->si_code = 1 si->si_pid = 3221225472 si->si_uid = 1869479936 si->si_status = 2712942 si->si_addr = 0xC0000000 <= 栈底地址 p = 0xC0000000
signo = 14 si = 0xBFFFF5A8 unused = 0xBFFFF628 si->si_signo = 14 si->si_errno = 0 si->si_code = 128 <= SI_KERNEL 0x80 Send by kernel. si->si_pid = 0 si->si_uid = 0 si->si_status = 896820224 si->si_addr = 0x00000000 ^Z [scz@ /home/scz/src]> bg %1 [scz@ /home/scz/src]> kill %1
signo = 15 si = 0xBFFFF5A8 unused = 0xBFFFF628 si->si_signo = 15 si->si_errno = 0 si->si_code = 0 <= SI_USER 0x00 Sent by kill, sigsend, raise. si->si_pid = 27712 <= kill()信号源 si->si_uid = 1000 <= kill()信号源 si->si_status = 896820224 si->si_addr = 0x00006C40 [scz@ /home/scz/src]> echo $$ 27712 [scz@ /home/scz/src]> id uid=1000(scz) gid=0(root) groups=0(root) [scz@ /home/scz/src]>
最后结论，对于x86/FreeBSD 4.5-RELEASE，无法利用该技术分辨kill()信号源。其 他三种操作系统可以利用该技术。
一个有趣的想法，进程分辨出kill()信号源，反向kill信号源。
D: [email protected] 2003-10-13 10:03
修改一下gstack.c，考虑栈向内存高址方向增长的情形。用递归方式确定堆栈增长方 向比较可靠，否则由于不同函数的不同优化可能导致误判，测试中碰上这种情形了。
/*
- For x86/Linux RedHat_8 2.4.18-14
- For x86/FreeBSD 4.5-RELEASE
- For SPARC/Solaris 8
- For AIX 4.3.3.0
- gcc -Wall -pipe -O3 -s -o gstack gstack.c */
/************************************************************************
-
* -
Head File * -
*
************************************************************************/
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <strings.h> #include <signal.h> #include <unistd.h> #include <setjmp.h>
/************************************************************************
-
* -
Macro * -
*
************************************************************************/
/*
- for signal handlers */ typedef void Sigfunc ( int, siginfo_t *, void * );
#define PRIVATE_SIG_ERR ((Sigfunc )-1) /
- 向上指向高址方向增长，向下指向低址方向增长，后者最常见 */ #define STACKUP 0 #define STACKDOWN 1
/************************************************************************
-
* -
Function Prototype * -
*
************************************************************************/
static unsigned char * get_stack_bottom ( void ); static void on_segvbus ( int signo, siginfo_t *si, void *unused ); static Sigfunc * PrivateSignal ( int signo, Sigfunc *func ); static Sigfunc * Signal ( int signo, Sigfunc *func ); static unsigned int stack_grow ( unsigned int level, unsigned int *addr );
/************************************************************************
-
* -
Static Global Var * -
*
************************************************************************/
/*
- start of .text / extern int _etext; /
- start of .data / extern int _edata; /
- start of heap */ extern int _end;
static sigjmp_buf jmpbuf; static volatile sig_atomic_t canjump = 0; static Sigfunc *orig_segv = PRIVATE_SIG_ERR; static Sigfunc *orig_bus = PRIVATE_SIG_ERR;
/************************************************************************/
static unsigned char * get_stack_bottom ( void ) { /* * for autovar, must be volatile */ volatile unsigned char *p = NULL;
orig_segv = Signal( SIGSEGV, on_segvbus );
orig_bus = Signal( SIGBUS , on_segvbus );
p = ( unsigned char * )&p;
if ( 0 != sigsetjmp( jmpbuf, 1 ) )
{
Signal( SIGSEGV, orig_segv );
Signal( SIGBUS , orig_bus );
goto get_stack_bottom_exit;
}
/*
* now sigsetjump() is OK
*/
canjump = 1;
if ( STACKUP == stack_grow( 0, NULL ) )
{
while ( 1 )
{
/*
* 诱发SIGSEGV、SIGBUS
*/
*p = *p;
p--;
}
}
else
{
while ( 1 )
{
/*
* 诱发SIGSEGV、SIGBUS
*/
*p = *p;
p++;
}
}get_stack_bottom_exit:
return( ( unsigned char * )p );} /* end of get_stack_bottom */
static void on_segvbus ( int signo, siginfo_t *si, void unused ) { fprintf ( stderr, "signo = %d\n" "si = 0x%08X\n" "unused = 0x%08X\n", signo, ( unsigned int )si, ( unsigned int )unused ); if ( NULL != si ) { fprintf ( stderr, "si->si_signo = %d\n" "si->si_errno = %d\n" "si->si_code = %d\n" "si->si_addr = 0x%08X\n", si->si_signo, si->si_errno, si->si_code, ( unsigned int )si->si_addr ); } if ( 0 == canjump ) { / * unexpected signal, ignore / return; } canjump = 0; / * jump back to get_stack_bottom, don't return / siglongjmp( jmpbuf, signo ); } / end of on_segvbus */
static Sigfunc * PrivateSignal ( int signo, Sigfunc *func ) { struct sigaction act, oact;
memset( &act, 0, sizeof( act ) );
sigemptyset( &act.sa_mask );
/*
* Invoke signal-catching function with three arguments instead of one.
*/
act.sa_flags = SA_SIGINFO;
act.sa_sigaction = func;
if ( SIGALRM == signo )
{#ifdef SA_INTERRUPT /* * SunOS 4.x / act.sa_flags |= SA_INTERRUPT; #endif } else { #ifdef SA_RESTART / * SVR4, 4.4BSD / act.sa_flags |= SA_RESTART; #endif } if ( sigaction( signo, &act, &oact ) < 0 ) { return( PRIVATE_SIG_ERR ); } return( oact.sa_sigaction ); } / end of PrivateSignal */
static Sigfunc * Signal ( int signo, Sigfunc *func ) { Sigfunc *sigfunc;
if ( PRIVATE_SIG_ERR == ( sigfunc = PrivateSignal( signo, func ) ) )
{
perror( "signal error" );
exit( EXIT_FAILURE );
}
return( sigfunc );} /* end of Signal */
static unsigned int stack_grow ( unsigned int level, unsigned int *addr ) { unsigned int dummy; unsigned int ret;
if ( 0 == level )
{
ret = stack_grow( level + 1, &dummy );
}
else
{
if ( ( unsigned int )addr > ( unsigned int )&dummy )
{
ret = STACKDOWN;
}
else
{
ret = STACKUP;
}
printf
(
"stack_level_0 = 0x%08X\n"
"stack_level_1 = 0x%08X\n"
"stack grow = %s/%u\n",
( unsigned int )addr,
( unsigned int )&dummy,
( STACKUP == ret ) ? "UP/HIGH" : "DOWN/LOW",
ret
);
}
return( ret );} /* end of stack_grow */
int main ( int argc, char * argv[] ) { unsigned char *p;
p = get_stack_bottom();
printf
(
"_etext = 0x%08X\n"
"_edata = 0x%08X\n"
"_end = 0x%08X\n"
"stack bottom = 0x%08X\n"
"&p = 0x%08X\n",
( unsigned int )&_etext,
( unsigned int )&_edata,
( unsigned int )&_end,
( unsigned int )p,
( unsigned int )&p
);
return( EXIT_SUCCESS );} /* end of main */
/************************************************************************/
这是在AIX 4.3.3.0上的执行效果:
./gstack stack_level_0 = 0x2FF22B40 stack_level_1 = 0x2FF22AF8 stack grow = DOWN/LOW/1 <= 栈向低址方向增长 signo = 11 si = 0x2FF22A10 unused = 0x2FF22780 si->si_signo = 11 si->si_errno = 0 si->si_code = 51 si->si_addr = 0x2FF23000 <= 栈底地址 _etext = 0x10000E40 _edata = 0x20000ED4 _end = 0x200010C0 stack bottom = 0x2FF23000 <= 栈底地址 &p = 0x2FF22BC8