Messages in this thread | | | Date | Fri, 6 Jul 2018 16:54:36 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] ipv4: fib: avoid NULL dereference |
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On Fri, Jul 06, 2018 at 08:39:11AM -0700, Eric Dumazet wrote: > > > On 07/06/2018 07:57 AM, Mark Rutland wrote: > > On Fri, Jul 06, 2018 at 07:47:04AM -0700, Eric Dumazet wrote: > >> > >> > >> On 07/06/2018 07:28 AM, Mark Rutland wrote: > >>> In tnode_free() we iterate over a callback_head list with a while loop. > >>> At the start of the loop body we generate the next head pointer, and at > >>> the end of the loop body we generate the tn pointer for the next > >>> iteration of the loop by using container_of() on the head pointer to > >>> find the tnode, and deriving the kv pointer from this. > >>> > >>> In the final iteration of the loop, this means that we derive a pointer > >>> from NULL, which is undefined behaviour, which UBSAN detects: > >> > >> There is no dereference, your patch title is misleading. > >> > >> UBSAN might be fooled, not the C compiler. > > > > I'm happy to change the title to "avoid undefined behaviour". > > > > Are you planning to change this as well ? > > include/linux/stddef.h:19:#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
No, because __builtin_offsetof() is used these days (since GCC 4), avoiding the undefined behaviour.
> (And probably dozens of other locations)
I do concede that if this is everywhere it's not worth the effort, and from the looks of things, the gnaliest cases are where we do things like:
get_user(var, &struct->field)
... where the user could validly pass a NULL pointer if it wished.
So I guess I'll give up.
Thanks, Mark.
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