2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------ !TASK_TRACED thread From: Oleg Nesterov <[email protected]> ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread CVE-2013-0871 BugLink: http://bugs.launchpad.net/bugs/1129192 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 <[email protected]> (cherry picked from commit 0666fb51b1483f27506e212cc7f7b2645b5c7acc) Signed-off-by: Luis Henriques <[email protected]> Acked-by: Colin King <[email protected]> Signed-off-by: Tim Gardner <[email protected]> Signed-off-by: Willy Tarreau <[email protected]> --- kernel/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 05625f6..d8184b5 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -506,7 +506,7 @@ static int ptrace_resume(struct task_struct *child, long request, long data) } child->exit_code = data; - wake_up_process(child); + wake_up_state(child, __TASK_TRACED); return 0; } -- 1.7.12.2.21.g234cd45.dirty -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
