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SubjectRe: [PATCH, for 2.6.29] ptrace: fix the usage of ptrace_fork()
On Mon, 9 Feb 2009 02:02:33 +0100
Oleg Nesterov <oleg@redhat.com> wrote:

> I noticed by pure accident we have ptrace_fork() and friends. This was
> added by "x86, bts: add fork and exit handling", commit
> bf53de907dfdaac178c92d774aae7370d7b97d20
>
> I can't test this, ds_request_bts() returns -EOPNOTSUPP, but I strongly
> believe this needs the fix. I think something like this program
>
> int main(void)
> {
> int pid = fork();
>
> if (!pid) {
> ptrace(PTRACE_TRACEME, 0, NULL, NULL);
> kill(getpid(), SIGSTOP);
> fork();
> } else {
> struct ptrace_bts_config bts = {
> .flags = PTRACE_BTS_O_ALLOC,
> .size = 4 * 4096,
> };
>
> wait(NULL);
>
> ptrace(PTRACE_SETOPTIONS, pid, NULL, PTRACE_O_TRACEFORK);
> ptrace(PTRACE_BTS_CONFIG, pid, &bts, sizeof(bts));
> ptrace(PTRACE_CONT, pid, NULL, NULL);
>
> sleep(1);
> }
>
> return 0;
> }
>
> should crash the kernel.
>
> If the task is traced by its natural parent ptrace_reparented() returns 0
> but we should clear ->btsxxx anyway.
>
> This is a minimal fix for 2.6.29, we need further cleanups imho.
>

This changelog is all a bit tentative-sounding.

>
> --- 6.29-rc3/kernel/fork.c~BTS_FIX 2009-01-29 01:13:55.000000000 +0100
> +++ 6.29-rc3/kernel/fork.c 2009-02-09 01:03:48.000000000 +0100
> @@ -1093,7 +1093,7 @@ static struct task_struct *copy_process(
> #ifdef CONFIG_DEBUG_MUTEXES
> p->blocked_on = NULL; /* not blocked yet */
> #endif
> - if (unlikely(ptrace_reparented(current)))
> + if (unlikely(current->ptrace))
> ptrace_fork(p, clone_flags);
>
> /* Perform scheduler related setup. Assign this task to a CPU. */

Can we please confirm that this patch is indeed correct and needed?


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