Messages in this thread | | | Date | Fri, 6 Jul 2018 15:36:04 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] radix-tree: avoid NULL dereference |
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On Fri, Jul 06, 2018 at 07:25:40AM -0700, Matthew Wilcox wrote: > On Fri, Jul 06, 2018 at 02:41:44PM +0100, Mark Rutland wrote: > > When idr_alloc() is called for the first time on an IDR (which has no > > nodes in its radix tree), we end up with calculate_count() calling > > get_slot_offset() with a NULL node, leading to a NULL pointer > > dereference caught by UBSAN: > > Thanks! > > > The result of the load is passed into node_tag_get(), which ignores the > > value when node is NULL. Typically, the compiler inlines both > > get_slot_offset() and node_tag_get() into calculate_count(), optimizing > > away the NULL-pointer dereference, and hence this doesn't typically > > result in a boot failure. > > > > We can't rely on the compiler always doing this, and must avoid > > dereferencing fields from node when it is potentially NULL. > > > > To do so, this patch folds the generation of offset into tag_get(), such > > that this only happens when node is not NULL. Callers are updated to > > pass the relevant slot, rather than the offset derived from it. > > I did think about this ... honest! My reasoning clearly glitched at some > point. I think this is the right way to fix the problem. > > Acked-by: Matthew Wilcox <willy@infradead.org>
Cheers!
I assume that Andrew will pick this up, if he's also happy with it.
Thanks, Mark.
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