Messages in this thread Patch in this message | | | Subject | Re: [regression] nf_iterate(), BUG: unable to handle kernel NULL pointer dereference | From | Pekka Enberg <> | Date | Thu, 24 Jul 2008 16:23:32 +0300 |
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On Thu, 2008-07-24 at 14:49 +0200, Patrick McHardy wrote: > Pekka Enberg wrote: > > On Thu, Jul 24, 2008 at 3:03 PM, Patrick McHardy <kaber@trash.net> wrote: > >> Ingo Molnar wrote: > >>> * Ingo Molnar <mingo@elte.hu> wrote: > >>> > >>>> here's a new type of crash a -tip testbox triggered today: > >>>> > >>>> BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 > >>>> IP: [<0000000000000000>] 0x0 > >>>> ... > >>>> Call Trace: > >>>> [<ffffffff80777f25>] ? ipv4_confirm+0x8d/0x122 > >>>> [<ffffffff80733107>] nf_iterate+0x43/0xa5 > >> Does reverting 31d8519c fix this? > > > > Hmm, why do you think it's related? It looks like elem->hook() is a > > NULL pointer but my patch shouldn't make any difference here... > > No, its already in ipv4_confirm, so its most likely helper->help() > thats NULL, which is contained in an extension. > > The reason why I think its this patch is (quoting from an old > email that I never got a response to):
Oh, I'm really sorry about that.
> --- > Your patch introduced a use-after-free and double-free. > krealloc() frees the old pointer, but it is still used > for the ->move operations, then freed again. > > To fix this I think we need a __krealloc() that doesn't > free the old memory, especially since it must not be > freed immediately because it may still be used in a RCU > read side (see the last part in the patch attached to > this mail (based on a kernel without your patch)).
Agreed. Something like this, perhaps?
[PATCH] netfilter: fix double-free and use-after free
As suggested by Patrick McHardy, introduce a __krealloc() that doesn't free the original buffer to fix a double-free and use-after-free bug introduced by me in netfilter that uses RCU.
Reported-by: Patrick McHardy <kaber@trash.net> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi> ---
diff --git a/include/linux/slab.h b/include/linux/slab.h index 9aa90a6..be6f1d4 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -96,6 +96,7 @@ int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr); /* * Common kmalloc functions provided by all allocators */ +void * __must_check __krealloc(const void *, size_t, gfp_t); void * __must_check krealloc(const void *, size_t, gfp_t); void kfree(const void *); size_t ksize(const void *); diff --git a/mm/util.c b/mm/util.c index 8f18683..6ef9e99 100644 --- a/mm/util.c +++ b/mm/util.c @@ -68,25 +68,22 @@ void *kmemdup(const void *src, size_t len, gfp_t gfp) EXPORT_SYMBOL(kmemdup); /** - * krealloc - reallocate memory. The contents will remain unchanged. + * __krealloc - like krealloc() but don't free @p. * @p: object to reallocate memory for. * @new_size: how many bytes of memory are required. * @flags: the type of memory to allocate. * - * The contents of the object pointed to are preserved up to the - * lesser of the new and old sizes. If @p is %NULL, krealloc() - * behaves exactly like kmalloc(). If @size is 0 and @p is not a - * %NULL pointer, the object pointed to is freed. + * This function is like krealloc() except it never frees the originally + * allocated buffer. Use this if you don't want to free the buffer immediately + * like, for example, with RCU. */ -void *krealloc(const void *p, size_t new_size, gfp_t flags) +void *__krealloc(const void *p, size_t new_size, gfp_t flags) { void *ret; size_t ks = 0; - if (unlikely(!new_size)) { - kfree(p); + if (unlikely(!new_size)) return ZERO_SIZE_PTR; - } if (p) ks = ksize(p); @@ -95,10 +92,37 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags) return (void *)p; ret = kmalloc_track_caller(new_size, flags); - if (ret && p) { + if (ret && p) memcpy(ret, p, ks); + + return ret; +} +EXPORT_SYMBOL(__krealloc); + +/** + * krealloc - reallocate memory. The contents will remain unchanged. + * @p: object to reallocate memory for. + * @new_size: how many bytes of memory are required. + * @flags: the type of memory to allocate. + * + * The contents of the object pointed to are preserved up to the + * lesser of the new and old sizes. If @p is %NULL, krealloc() + * behaves exactly like kmalloc(). If @size is 0 and @p is not a + * %NULL pointer, the object pointed to is freed. + */ +void *krealloc(const void *p, size_t new_size, gfp_t flags) +{ + void *ret; + + if (unlikely(!new_size)) { kfree(p); + return ZERO_SIZE_PTR; } + + ret = __krealloc(p, new_size, flags); + if (ret && p != ret) + kfree(p); + return ret; } EXPORT_SYMBOL(krealloc); diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c index 3469bc7..c956ef7 100644 --- a/net/netfilter/nf_conntrack_extend.c +++ b/net/netfilter/nf_conntrack_extend.c @@ -95,7 +95,7 @@ void *__nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp) newlen = newoff + t->len; rcu_read_unlock(); - new = krealloc(ct->ext, newlen, gfp); + new = __krealloc(ct->ext, newlen, gfp); if (!new) return NULL;
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