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Replace suspicious popen_pid assignment with an obviously correct one

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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>
This commit is contained in:
Denys Vlasenko 2013-07-02 11:31:24 +02:00
parent d0ffdf494a
commit 519af5ad34
1 changed files with 5 additions and 3 deletions
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8
strace.c
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@ -485,6 +485,7 @@ static FILE *
strace_popen(const char *command)
{
FILE *fp;
int pid;
int fds[2];
swap_uid();
@ -493,11 +494,11 @@ strace_popen(const char *command)
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 @@ strace_popen(const char *command)
}
/* parent */
popen_pid = pid;
close(fds[0]);
swap_uid();
fp = fdopen(fds[1], "w");