Messages in this thread | | | Date | Tue, 8 Aug 2006 20:31:59 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] sys_getppid oopses on debug kernel |
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On 09 Aug 2006 05:09:11 +0200 Andi Kleen <ak@suse.de> wrote:
> Kirill Korotaev <dev@sw.ru> writes: > > [adding linux-arch] > > > > 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? > > no, read the comment in sys_getppid. > > It is a valid optimization. _safe_ and alowing to bypass taking the lock. > > BUT! This optimization relies on the fact that kernel memory (DMA + normal zone) > > is always mapped into virtual address space. > > Which is invalid for debug kernels only. > > In x86 arch code we would use __get_user for this (and we do in a couple > of places). But it wouldn't be portable because sometimes _user is > in a different address space. > > Maybe it would be time to make a similar facility (read/write_kernel_safe() or similar) > with error return available to generic code? > > It should be easy to implement - iirc near all architectures already > use the exception handling frame work and it is a simple extension > of that. x86 could just define it to __put/get_user >
I just did something like that:
Similar to ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.18-rc3/2.6.18-rc3-mm2/broken-out/add-probe_kernel_address.patch
Although I'm not sure it's needed for this problem. A getppid() which does
asmlinkage long sys_getppid(void) { int pid;
read_lock(&tasklist_lock); pid = current->group_leader->real_parent->tgid; read_unlock(&tasklist_lock);
return pid; }
seems like a fine implementation to me ;) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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