Messages in this thread | | | Subject | Re: [PATCH] sys_getppid oopses on debug kernel | From | Dave Hansen <> | Date | Tue, 08 Aug 2006 08:26:57 -0700 |
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On Tue, 2006-08-08 at 14:22 +0400, Kirill Korotaev wrote: > sys_getppid() optimization can access a freed memory. > On kernels with DEBUG_SLAB turned ON, this results in > Oops. ... > +#else > + /* > + * ->real_parent could be released before dereference and > + * we accessed freed kernel memory, which faults with debugging on. > + * Keep it simple and stupid. > + */ > + read_lock(&tasklist_lock); > + pid = current->group_leader->real_parent->tgid; > + read_unlock(&tasklist_lock); > +#endif > return pid; > }
Accessing freed memory is a bug, always, not just *only* when slab debugging is on, right? Doesn't this mean we could get junk, or that the reader could potentially run off a bad pointer?
It seems that this patch only papers over the problem in the case when it is observed, but doesn't really even fix the normal case.
Could we use a seqlock to determine when real_parent is in flux, and re-read real_parent until we get a consistent one? We could use in in lieu of the existing for() loop.
-- Dave
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