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Date: Wed, 26 Jun 2019 00:18:05 +0100
From: Radostin Stoyanov <rstoyanov1@...il.com>
To: musl@...ts.openwall.com
Cc: dalias@...ifal.cx
Subject: seccomp causes pthread_join() to hang
Hello,
In the test suite of CRIU [1] we have noticed an interesting bug which
is caused by commit 8f11e6127fe93093f81a52b15bb1537edc3fc8af ("track all
live threads in an AS-safe, fully-consistent linked list") [2].
When seccomp is used in a multithreaded application it may cause
pthread_join() to hang.
This is a minimal application to reproduce the issue:
#include <errno.h>
#include <seccomp.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
static void *fn()
{
scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_KILL);
if (!ctx) {
perror("seccomp_init");
goto err;
}
if (seccomp_load(ctx) < 0) {
perror("seccomp_load");
goto err;
}
/* This should cause SIG_KILL */
getpid();
err:
return (void *)1;
}
int main()
{
pthread_t t1;
if (pthread_create(&t1, NULL, fn, NULL)) {
perror("pthread_create");
return -1;
}
if (pthread_join(t1, NULL)) {
perror("pthread_join");
return -1;
}
return 0;
}
Expected behaviour: Thread t1 should receive SIG_KILL and the main
thread should return 0.
Actual behaviour: pthread_join() hangs.
Reproducibility: Always
Regression: Yes
This bug can be reproduced with Alpine 3.10 ($ docker run -it
alpine:3.10 sh).
[1] https://criu.org/
[2]
https://git.musl-libc.org/cgit/musl/commit/?id=8f11e6127fe93093f81a52b15bb1537edc3fc8af
Kind regards,
Radostin
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