Replace suspicious popen_pid assignment with an obviously correct one
popen_pid = vfork() does work correctly, but for a subtle reason
that wrong assignment of 0 happens in the child _first_,
and _then_ correct value overwrites it in the parent.
(And in a hyphothetical system where vfork = fork,
popen_pid wouldn't be shared, so it will also be ok.)
However, it's not necessary to be difficult.
This change makes it so that assignment is done only in parent.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/strace.c b/strace.c
index 4c70b98..2741201 100644
--- a/strace.c
+++ b/strace.c
@@ -485,6 +485,7 @@
strace_popen(const char *command)
{
FILE *fp;
+ int pid;
int fds[2];
swap_uid();
@@ -493,11 +494,11 @@
set_cloexec_flag(fds[1]); /* never fails */
- popen_pid = vfork();
- if (popen_pid == -1)
+ pid = vfork();
+ if (pid < 0)
perror_msg_and_die("vfork");
- if (popen_pid == 0) {
+ if (pid == 0) {
/* child */
close(fds[1]);
if (fds[0] != 0) {
@@ -510,6 +511,7 @@
}
/* parent */
+ popen_pid = pid;
close(fds[0]);
swap_uid();
fp = fdopen(fds[1], "w");