The patch titled
ptrace: copy_process() should disable stepping
has been added to the -mm tree. Its filename is
ptrace-copy_process-should-disable-stepping.patch
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------------------------------------------------------
Subject: ptrace: copy_process() should disable stepping
From: Oleg Nesterov <oleg@xxxxxxxxxx>
If the tracee calls fork() after PTRACE_SINGLESTEP, the forked child
starts with TIF_SINGLESTEP/X86_EFLAGS_TF bits copied from ptraced parent.
This is not right, especially when the new child is not auto-attaced: in
this case it is killed by SIGTRAP.
Change copy_process() to call user_disable_single_step(). Tested on x86.
Test-case:
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <assert.h>
int main(void)
{
int pid, status;
if (!(pid = fork())) {
assert(ptrace(PTRACE_TRACEME) == 0);
kill(getpid(), SIGSTOP);
if (!fork()) {
/* kernel bug: this child will be killed by SIGTRAP */
printf("Hello world\n");
return 43;
}
wait(&status);
return WEXITSTATUS(status);
}
for (;;) {
assert(pid == wait(&status));
if (WIFEXITED(status))
break;
assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0);
}
assert(WEXITSTATUS(status) == 43);
return 0;
}
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN kernel/fork.c~ptrace-copy_process-should-disable-stepping kernel/fork.c
--- a/kernel/fork.c~ptrace-copy_process-should-disable-stepping
+++ a/kernel/fork.c
@@ -1203,9 +1203,10 @@ static struct task_struct *copy_process(
p->sas_ss_sp = p->sas_ss_size = 0;
/*
- * Syscall tracing should be turned off in the child regardless
- * of CLONE_PTRACE.
+ * Syscall tracing and stepping should be turned off in the
+ * child regardless of CLONE_PTRACE.
*/
+ user_disable_single_step(p);
clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
#ifdef TIF_SYSCALL_EMU
clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
linux-next.patch
itimers-fix-racy-writes-to-cpu_itimer-fields.patch
posix-cpu-timers-optimize-and-document-timer_create-callback.patch
ptrace-cleanup-ptrace_init_task-ptrace_link-path.patch
ptrace-copy_process-should-disable-stepping.patch
signals-send_sig_noinfo-should-be-considered-as-si_fromuser.patch
signals-send_signal-use-si_fromuser-to-detect-from_ancestor_ns.patch
signals-cosmetic-collect_signal-use-si_user.patch
signals-kill-force_sig_specific.patch
signals-check-group_stop_count-after-tracehook_get_signal.patch
utrace-core.patch
do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch
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