From: Alexey Izbyshev <izbyshev@ispras.ru>
To: musl@lists.openwall.com
Subject: [musl] Potentially infinite loop in posix_spawn'ed child
Date: Mon, 24 May 2021 13:09:21 +0300 [thread overview]
Message-ID: <985e15962c164eb3076752d6ee4c05fe@ispras.ru> (raw)
[-- Attachment #1: Type: text/plain, Size: 912 bytes --]
Hi,
I've noticed the following loop at
https://git.musl-libc.org/cgit/musl/tree/src/process/posix_spawn.c#n159:
exec(args->path, args->argv, args->envp);
ret = -errno;
fail:
/* Since sizeof errno < PIPE_BUF, the write is atomic. */
ret = -ret;
if (ret) while (__syscall(SYS_write, p, &ret, sizeof ret) < 0);
_exit(127);
Is there any reason that write is done in a loop? If SIGPIPE is blocked
or ignored and the parent dies before this point, the child will spin in
it forever.
A test case is attached. It overrides execve() to abuse it as a
callback, avoiding reliance on timings.
As an aside, perhaps it would make sense to call execve() in
posix_spawn() implementation via a hidden symbol? This would both make
it consistent with posix_spawnp() and avoid any trouble with user code
executing in a vfork'ed child if execve() is overridden via e.g.
LD_PRELOAD.
Alexey
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: test.c --]
[-- Type: text/x-c; name=test.c, Size: 440 bytes --]
#include <errno.h>
#include <signal.h>
#include <spawn.h>
#include <unistd.h>
static int p[2];
int execve(const char *path, char *const argv[], char *const envp[]) {
close(p[1]);
kill(getppid(), SIGKILL);
read(p[0], &(char){0}, 1);
errno = ENOENT;
return -1;
}
int main(int argc, char *argv[], char *envp[]) {
signal(SIGPIPE, SIG_IGN);
pipe(p);
posix_spawn(0L, "/non-existing", 0L, 0L, argv, envp);
return 0;
}
next reply other threads:[~2021-05-24 10:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-24 10:09 Alexey Izbyshev [this message]
2021-05-24 15:40 ` Szabolcs Nagy
2021-05-24 16:50 ` Alexey Izbyshev
2021-05-24 20:33 ` Rich Felker
2021-05-25 6:30 ` Alexey Izbyshev
2021-05-25 14:32 ` Rich Felker
2024-02-29 14:03 ` Alexey Izbyshev
2024-02-29 15:35 ` Rich Felker
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