thirdparty/util-linux
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script: fix race conditions

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script(1) uses three processes (doinput, dooutput and doshell).  It's
possible that the shell process is finished before the input and
output processes are completely initialized. For example:

  $ script -c "printf Bingo"

In particular case the output and input processes read/write data from
shell process in time when the shell process is already done -- so it
hangs on read().

The second problem is that the output process can finish although
there are unread data from finished shell process -- an output in
the typescript file and on terminal is incomplete!

script(1) has to pass:

 $ for i in `seq 1 1000`; do script -q -c "printf 'Bingo\n'"; done | grep -c Bingo
 1000

without problems.

Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2007-08-07 00:36:31 +02:00
parent a512390d92
commit 1f58c445c6
1 changed files with 52 additions and 10 deletions
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62
misc-utils/script.c
View file

@ -52,6 +52,7 @@
#include <sys/time.h>
#include <sys/file.h>
#include <sys/signal.h>
#include <errno.h>
#include "nls.h"
#ifdef __linux__
@ -97,6 +98,8 @@ int tflg = 0;
static char *progname;
int die;
static void
die_if_link(char *fn) {
struct stat s;
@ -123,6 +126,7 @@ die_if_link(char *fn) {
int
main(int argc, char **argv) {
struct sigaction sa;
extern int optind;
char *p;
int ch;
@ -191,7 +195,12 @@ main(int argc, char **argv) {
printf(_("Script started, file is %s\n"), fname);
fixtty();
(void) signal(SIGCHLD, finish);
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_handler = finish;
sigaction(SIGCHLD, &sa, NULL);
child = fork();
if (child < 0) {
perror("fork");
@ -207,8 +216,10 @@ main(int argc, char **argv) {
dooutput();
else
doshell();
} else
(void) signal(SIGWINCH, resize);
} else {
sa.sa_handler = resize;
sigaction(SIGWINCH, &sa, NULL);
}
doinput();
return 0;
@ -221,8 +232,12 @@ doinput() {
(void) fclose(fscript);
while ((cc = read(0, ibuf, BUFSIZ)) > 0)
if (die == 0 && child && kill(child, 0) == -1 && errno == ESRCH)
die = 1;
while (die == 0 && (cc = read(0, ibuf, BUFSIZ)) > 0)
(void) write(master, ibuf, cc);
done();
}
@ -232,14 +247,10 @@ void
finish(int dummy) {
int status;
register int pid;
register int die = 0;
while ((pid = wait3(&status, WNOHANG, 0)) > 0)
if (pid == child)
die = 1;
if (die)
done();
}
void
@ -267,6 +278,7 @@ dooutput() {
char obuf[BUFSIZ];
struct timeval tv;
double oldtime=time(NULL), newtime;
int flgs = 0;
(void) close(0);
#ifdef HAVE_LIBUTIL
@ -277,10 +289,37 @@ dooutput() {
if (!qflg)
fprintf(fscript, _("Script started on %s"), obuf);
for (;;) {
if (die == 0 && child && kill(child, 0) == -1 && errno == ESRCH)
/*
* the SIGCHLD handler could be executed when the "child"
* variable is not set yet. It means that the "die" is zero
* althought the child process is already done. We have to
* check this thing now. Now we have the "child" variable
* already initialized. For more details see main() and
* finish(). --kzak 07-Aug-2007
*/
die = 1;
do {
if (die && flgs == 0) {
/* ..child is dead, but it doesn't mean that there is
* nothing in buffers.
*/
flgs = fcntl(master, F_GETFL, 0);
if (fcntl(master, F_SETFL, (flgs | O_NONBLOCK)) == -1)
break;
}
if (tflg)
gettimeofday(&tv, NULL);
errno = 0;
cc = read(master, obuf, sizeof (obuf));
if (die && errno == EINTR && cc <= 0)
/* read() has been interrupted by SIGCHLD, try it again
* with O_NONBLOCK
*/
continue;
if (cc <= 0)
break;
if (tflg) {
@ -292,7 +331,10 @@ dooutput() {
(void) fwrite(obuf, 1, cc, fscript);
if (fflg)
(void) fflush(fscript);
}
} while(1);
if (flgs)
fcntl(master, F_SETFL, flgs);
done();
}