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Instead of using a array to store received signals, open a pipe and

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have the signal handler write the signal number to one end and
select() on the other end.  This makes it possible to handle signals
similar to I/O without race conditions.
This commit is contained in:
Todd C. Miller
2010-09-10 11:20:32 -04:00
parent f601085de4
commit 59399d55c3
3 changed files with 239 additions and 85 deletions
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42
src/exec_pty.c
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@@ -567,6 +567,8 @@ fork_pty(struct command_details *details, char *argv[], char *envp[],
case 0:
/* child */
close(sv[0]);
close(signal_pipe[0]);
close(signal_pipe[1]);
fcntl(sv[1], F_SETFD, FD_CLOEXEC);
if (exec_setup(details, slavename, io_fds[SFD_SLAVE]) == TRUE) {
/* Close the other end of the stdin/stdout/stderr pipes and exec. */
@@ -797,7 +799,7 @@ handle_sigchld(int backchannel, struct command_status *cstat)
* parent and relays signals from the parent to the command.
* Returns an error if fork(2) fails, else calls _exit(2).
*/
int
static int
exec_monitor(struct command_details *details, char *argv[], char *envp[],
int backchannel)
{
@@ -807,6 +809,7 @@ exec_monitor(struct command_details *details, char *argv[], char *envp[],
sigaction_t sa;
int errpipe[2], maxfd, n, status;
int alive = TRUE;
unsigned char signo;
/* Close unused fds. */
if (io_fds[SFD_MASTER] != -1)
@@ -814,6 +817,13 @@ exec_monitor(struct command_details *details, char *argv[], char *envp[],
if (io_fds[SFD_USERTTY] != -1)
close(io_fds[SFD_USERTTY]);
/*
* We use a pipe to atomically handle signal notification within
* the select() loop.
*/
if (pipe_nonblock(signal_pipe) != 0)
error(1, "cannot create pipe");
/* Reset SIGWINCH and SIGALRM. */
zero_bytes(&sa, sizeof(sa));
sigemptyset(&sa.sa_mask);
@@ -872,6 +882,8 @@ exec_monitor(struct command_details *details, char *argv[], char *envp[],
if (child == 0) {
/* We pass errno back to our parent via pipe on exec failure. */
close(backchannel);
close(signal_pipe[0]);
close(signal_pipe[1]);
close(errpipe[0]);
fcntl(errpipe[1], F_SETFD, FD_CLOEXEC);
@@ -905,27 +917,20 @@ exec_monitor(struct command_details *details, char *argv[], char *envp[],
}
/* Wait for errno on pipe, signal on backchannel or for SIGCHLD */
maxfd = MAX(errpipe[0], backchannel);
maxfd = MAX(MAX(errpipe[0], signal_pipe[0]), backchannel);
fdsr = (fd_set *)emalloc2(howmany(maxfd + 1, NFDBITS), sizeof(fd_mask));
zero_bytes(fdsr, howmany(maxfd + 1, NFDBITS) * sizeof(fd_mask));
zero_bytes(&cstat, sizeof(cstat));
tv.tv_sec = 0;
tv.tv_usec = 0;
for (;;) {
/* Read child status. */
if (recvsig[SIGCHLD]) {
recvsig[SIGCHLD] = FALSE;
alive = handle_sigchld(backchannel, &cstat);
}
/* Check for signal on backchannel or errno on errpipe. */
FD_SET(backchannel, fdsr);
FD_SET(signal_pipe[0], fdsr);
if (errpipe[0] != -1)
FD_SET(errpipe[0], fdsr);
maxfd = MAX(errpipe[0], backchannel);
maxfd = MAX(MAX(errpipe[0], signal_pipe[0]), backchannel);
if (recvsig[SIGCHLD])
continue;
/* If command exited we just poll, there may be data on errpipe. */
n = select(maxfd + 1, fdsr, NULL, NULL, alive ? NULL : &tv);
if (n <= 0) {
@@ -936,6 +941,21 @@ exec_monitor(struct command_details *details, char *argv[], char *envp[],
error(1, "select failed");
}
if (FD_ISSET(signal_pipe[0], fdsr)) {
/* Read child status. */
n = read(signal_pipe[0], &signo, sizeof(signo));
if (n == -1) {
if (errno == EINTR || errno == EAGAIN)
continue;
warning("error reading from signal pipe");
goto done;
}
/* We should only ever get SIGCHLD. */
if (signo == SIGCHLD) {
alive = handle_sigchld(backchannel, &cstat);
continue;
}
}
if (errpipe[0] != -1 && FD_ISSET(errpipe[0], fdsr)) {
/* read errno or EOF from command pipe */
n = read(errpipe[0], &cstat, sizeof(cstat));