From: Benjamin Berg <benja...@sipsolutions.net>
When in seccomp mode, we would hang forever on the futex if a child has
died unexpectedly. In contrast, ptrace mode will notice it and kill the
corresponding thread when it fails to run it.
Fix this issue by simply printing a message and aborting. In this case
something from the outside (e.g. OOM killer) has interferred with the
machine and it is reasonable to not try to recover.
Signed-off-by: Benjamin Berg <benja...@sipsolutions.net>
---
arch/um/include/shared/os.h | 1 +
arch/um/os-Linux/process.c | 40 +++++++++++++++++++++++++++++++++++++
arch/um/os-Linux/signal.c | 7 +++++++
3 files changed, 48 insertions(+)
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index d1f1dedad83b..07683f45d7e1 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -192,6 +192,7 @@ extern void get_host_cpu_features(
extern int create_mem_file(unsigned long long len);
/* process.c */
+void os_check_child_lost(void);
extern unsigned long os_process_pc(int pid);
extern int os_process_parent(int pid);
extern void os_alarm_process(int pid);
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index e52dd37ddadc..db98fc79d9e2 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -17,6 +17,7 @@
#include <init.h>
#include <longjmp.h>
#include <os.h>
+#include <skas/skas.h>
#define ARBITRARY_ADDR -1
#define FAILURE_PID -1
@@ -102,9 +103,18 @@ void os_stop_process(int pid)
void os_kill_process(int pid, int reap_child)
{
+ sigset_t chld;
+
+ /* Block SIGCHLD so that we can reap it before the handler runs. */
+ sigemptyset(&chld);
+ sigaddset(&chld, SIGCHLD);
+ sigprocmask(SIG_BLOCK, &chld, NULL);
+
kill(pid, SIGKILL);
if (reap_child)
CATCH_EINTR(waitpid(pid, NULL, __WALL));
+
+ sigprocmask(SIG_UNBLOCK, &chld, NULL);
}
/* Kill off a ptraced child by all means available. kill it normally first,
@@ -114,11 +124,39 @@ void os_kill_process(int pid, int reap_child)
void os_kill_ptraced_process(int pid, int reap_child)
{
+ sigset_t chld;
+
+ /* Block SIGCHLD so that we can reap it before the handler runs. */
+ sigemptyset(&chld);
+ sigaddset(&chld, SIGCHLD);
+ sigprocmask(SIG_BLOCK, &chld, NULL);
+
kill(pid, SIGKILL);
ptrace(PTRACE_KILL, pid);
ptrace(PTRACE_CONT, pid);
if (reap_child)
CATCH_EINTR(waitpid(pid, NULL, __WALL));
+
+ sigprocmask(SIG_UNBLOCK, &chld, NULL);
+}
+
+void os_check_child_lost(void)
+{
+ int status;
+ pid_t pid;
+
+ /*
+ * Check if we can reap a child.
+ * Any expected kills will clean up without this handler being fired.
+ */
+ pid = waitpid(-1, &status, WNOHANG);
+ if (pid <= 0)
+ return;
+
+ os_warn("Child %d died unexpectedly with status %d, cannot recover in
seccomp mode!\r\n",
+ pid, status);
+ /* Kill ourselves including all children. */
+ killpg(os_getpid(), SIGABRT);
}
/* Don't use the glibc version, which caches the result in TLS. It misses some
@@ -283,5 +321,7 @@ void init_new_thread_signals(void)
set_handler(SIGBUS);
signal(SIGHUP, SIG_IGN);
set_handler(SIGIO);
+ if (using_seccomp)
+ set_handler(SIGCHLD);
signal(SIGWINCH, SIG_IGN);
}
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 24a403a70a02..d8c92e04c873 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -108,6 +108,11 @@ static void timer_real_alarm_handler(mcontext_t *mc)
timer_handler(SIGALRM, NULL, ®s);
}
+static void sig_child_handler(int sig, struct siginfo *unused_si, mcontext_t
*mc)
+{
+ os_check_child_lost();
+}
+
void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
{
int enabled;
@@ -169,6 +174,8 @@ static void (*handlers[_NSIG])(int sig, struct siginfo *si,
mcontext_t *mc) = {
[SIGIO] = sig_handler,
[SIGWINCH] = sig_handler,
+ /* SIGCHLD is only registered in seccomp mode. */
+ [SIGCHLD] = sig_child_handler,
[SIGALRM] = timer_alarm_handler,
[SIGUSR1] = sigusr1_handler,
--
2.38.1
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