On Sat, 7 May 2011 11:14:14 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> Andrew Morton wrote:
> > > char *strncpy(char *dest, const char *src, size_t n)
> > > {
> > > size_t len = __strnend(src, n) - src;
>
> If src was overwritten by prctl(PR_SET_NAME) at this moment (i.e. after len was
> calculated),
>
> > > __builtin_memset(dest + len, 0, n - len);
> > > __builtin_memcpy(dest, src, len);
>
> won't this result in inconsistent copying of src when length of src has changed
> by prctl(PR_SET_NAME)?
>
> > > return dest;
> > > }
>
> This strncpy() assumes that length of src won't change within the function.
> I thought prctl(PR_SET_NAME) might break such assumption.
PR_SET_NAME uses set_task_comm() which has appropriate locking to
protect against get_task_comm().
If kernel code directly accesses task->comm without taking task_lock()
then yes, it's racy.
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