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Fix a race between when we get the child pid in the parent and when

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the child process exits.  The problem exhibited as a hang after a
short-lived process, e.g. "sudo id" when no IO logger was enabled.
This commit is contained in:
Todd C. Miller
2010-04-08 06:12:47 -04:00
parent 29f22dba2d
commit a3f4278388
1 changed files with 19 additions and 32 deletions
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51
src/script.c
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@@ -111,7 +111,6 @@ static void flush_output(struct script_buf *output);
static void handler(int s);
static int script_child(const char *path, char *argv[], char *envp[], int, int);
static void script_run(const char *path, char *argv[], char *envp[], int);
static void sigchild(int s);
static void sigwinch(int s);
static void sync_ttysize(int src, int dst);
static void deliver_signal(pid_t pid, int signo);
@@ -349,7 +348,7 @@ script_execve(struct command_details *details, char *argv[], char *envp[],
/* Note: HP-UX select() will not be interrupted if SA_RESTART set */
sa.sa_flags = 0;
sa.sa_handler = sigchild;
sa.sa_handler = handler;
sigaction(SIGCHLD, &sa, NULL);
if (log_io) {
@@ -473,10 +472,25 @@ script_execve(struct command_details *details, char *argv[], char *envp[],
zero_bytes(&input, sizeof(input));
zero_bytes(&output, sizeof(output));
for (;;) {
/* XXX - racey */
if (!relaysig && recvsig != SIGCHLD) {
relaysig = recvsig;
/* Wait for children as needed. */
if (recvsig == SIGCHLD) {
pid_t pid;
int flags = WNOHANG;
recvsig = 0;
if (log_io)
flags |= WUNTRACED;
do {
do {
pid = waitpid(child, &child_status, flags);
} while (pid == -1 && errno == EINTR);
if (pid == child) {
if (!log_io)
recvsig = SIGCHLD; /* XXX - hacky, see below */
else if (WIFSTOPPED(child_status))
relaysig = WSTOPSIG(child_status);
}
} while (pid > 0);
}
/* If not logging I/O and child has exited we are done. */
@@ -942,33 +956,6 @@ sync_ttysize(int src, int dst)
#endif
}
/*
* Handler for SIGCHLD in parent
* Note that this will detect when the child monitoring the command exits,
* not the command itself.
*/
static void
sigchild(int s)
{
pid_t pid;
int flags = WNOHANG;
int serrno = errno;
if (!tq_empty(&io_plugins))
flags |= WUNTRACED;
do {
pid = waitpid(child, &child_status, flags);
} while (pid == -1 && errno == EINTR);
if (pid == child) {
if (tq_empty(&io_plugins))
recvsig = SIGCHLD;
else if (WIFSTOPPED(child_status))
recvsig = WSTOPSIG(child_status);
}
errno = serrno;
}
/*
* Generic handler for signals passed from parent -> child
*/