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authorOleg Nesterov <oleg@redhat.com>2011-05-25 19:20:21 +0200
committerOleg Nesterov <oleg@redhat.com>2011-05-25 19:20:21 +0200
commit0666fb51b1483f27506e212cc7f7b2645b5c7acc (patch)
treeceb625d70f0c730a46e2d954b74d687cc36b0030 /kernel/ptrace.c
parent22e12bbc9bc38c6d0bd541d061a0f547596fc19d (diff)
ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread
It is not clear why ptrace_resume() does wake_up_process(). Unless the caller is PTRACE_KILL the tracee should be TASK_TRACED so we can use wake_up_state(__TASK_TRACED). If sys_ptrace() races with SIGKILL we do not need the extra and potentionally spurious wakeup. If the caller is PTRACE_KILL, wake_up_process() is even more wrong. The tracee can sleep in any state in any place, and if we have a buggy code which doesn't handle a spurious wakeup correctly PTRACE_KILL can be used to exploit it. For example: int main(void) { int child, status; child = fork(); if (!child) { int ret; assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0); ret = pause(); printf("pause: %d %m\n", ret); return 0x23; } sleep(1); assert(ptrace(PTRACE_KILL, child, 0,0) == 0); assert(child == wait(&status)); printf("wait: %x\n", status); return 0; } prints "pause: -1 Unknown error 514", -ERESTARTNOHAND leaks to the userland. In this case sys_pause() is buggy as well and should be fixed. I do not know what was the original rationality behind PTRACE_KILL. The man page is simply wrong and afaics it was always wrong. Imho it should be deprecated, or may be it should do send_sig(SIGKILL) as Denys suggests, but in any case I do not think that the current behaviour was intentional. Note: there is another problem, ptrace_resume() changes ->exit_code and this can race with SIGKILL too. Eventually we should change ptrace to not use ->exit_code. Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 7a81fc07134..2df115790cd 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -562,7 +562,7 @@ static int ptrace_resume(struct task_struct *child, long request,
}
child->exit_code = data;
- wake_up_process(child);
+ wake_up_state(child, __TASK_TRACED);
return 0;
}