From: Eric Dumazet <eric.dumazet@gmail•com>
To: David Miller <davem@davemloft•net>
Cc: emil.s.tantilov@intel•com, emils.tantilov@gmail•com,
netdev@vger•kernel.org, jesse.brandeburg@intel•com,
jeffrey.t.kirsher@intel•com, jolsa@redhat•com,
Patrick McHardy <kaber@trash•net>,
"Paul E. McKenney" <paulmck@linux•vnet.ibm.com>
Subject: Re: [PATCH] net: sk_prot_alloc() should not blindly overwrite memory
Date: Thu, 09 Jul 2009 07:36:05 +0200 [thread overview]
Message-ID: <4A5581C5.5070409@gmail.com> (raw)
In-Reply-To: <4A5441A0.3050504@gmail.com>
Eric Dumazet a écrit :
> David Miller a écrit :
>> From: Eric Dumazet <eric.dumazet@gmail•com>
>> Date: Wed, 08 Jul 2009 00:33:29 +0200
>>
>>> [PATCH] net: sk_prot_alloc() should not blindly overwrite memory
>>>
>>> Some sockets use SLAB_DESTROY_BY_RCU, and our RCU code rely that some
>>> fields should not be blindly overwritten, even with null.
>>>
>>> These fields are sk->sk_refcnt and sk->sk_nulls_node.next
>>>
>>> Current sk_prot_alloc() implementation doesnt respect this hypothesis,
>>> calling kmem_cache_alloc() with __GFP_ZERO and setting sk_refcnt to 1
>>> instead of atomically increment it.
>>>
>>> Reported-by: Emil S Tantilov <emils.tantilov@gmail•com>
>>> Signed-off-by: Eric Dumazet <eric.dumazet@gmail•com>
>> I've applied this but will wait for some more testing before
>> I push it out for real to kernel.org
>
> Thanks David
>
> I forgot to CC Paul and Patrick, so I'll ask them to look at this patch.
>
> Patrick, a similar fix is needed in conntrack as well, we currently
> uses "ct = kmem_cache_zalloc(nf_conntrack_cachep, gfp);" and thus
> overwrite struct hlist_nulls_node hnnode; contained
> in "struct nf_conntrack_tuple_hash", while lockless readers still
> potentialy need them. Setting hnnode.next to NULL is dangerous
> since last bit is not set (not a nulls value), a reader could
> try to dereference this NULL pointer and trap.
>
>
> Here is the patch again so that Paul & Patrick can comment on it.
>
> I am not sure about the refcnt thing (blindly setting it to 0 again
> should be OK in fact, since no reader should/can to the
> atomic_inc_if_not_zero on it), but the nulls.next thing is problematic.
Here is an updated and much simpler patch, taking care of sk_node.next being not set to 0
This patch applies to >= 2.6.29 kernels
[PATCH] net: sk_prot_alloc() should not blindly overwrite memory
Some sockets use SLAB_DESTROY_BY_RCU, and our RCU code correctness
depends on sk->sk_nulls_node.next being always valid. A NULL
value is not allowed as it might fault a lockless reader.
Current sk_prot_alloc() implementation doesnt respect this hypothesis,
calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around
the forbidden field.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail•com>
---
diff --git a/net/core/sock.c b/net/core/sock.c
index b0ba569..7b87ec0 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -939,8 +939,23 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
struct kmem_cache *slab;
slab = prot->slab;
- if (slab != NULL)
- sk = kmem_cache_alloc(slab, priority);
+ if (slab != NULL) {
+ sk = kmem_cache_alloc(slab, priority & ~__GFP_ZERO);
+ if (!sk)
+ return sk;
+ if (priority & __GFP_ZERO) {
+ /*
+ * caches using SLAB_DESTROY_BY_RCU should let
+ * sk_node.next un-modified. Special care is taken
+ * when initializing object to zero.
+ */
+ if (offsetof(struct sock, sk_node.next) != 0)
+ memset(sk, 0, offsetof(struct sock, sk_node.next));
+ memset(&sk->sk_node.pprev, 0,
+ prot->obj_size - offsetof(struct sock,
+ sk_node.pprev));
+ }
+ }
else
sk = kmalloc(prot->obj_size, priority);
next prev parent reply other threads:[~2009-07-09 5:36 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-01 18:08 WARNING: at include/net/sock.h:417 udp_lib_unhash Tantilov, Emil S
2009-07-02 6:10 ` Eric Dumazet
2009-07-07 0:54 ` Emil S Tantilov
2009-07-07 7:21 ` Eric Dumazet
2009-07-07 7:40 ` Eric Dumazet
2009-07-07 16:14 ` [PATCH] net: sk_alloc() should not blindly overwrite memory Eric Dumazet
2009-07-07 18:33 ` Tantilov, Emil S
2009-07-07 22:33 ` [PATCH] net: sk_prot_alloc() " Eric Dumazet
2009-07-08 2:14 ` David Miller
2009-07-08 6:50 ` Eric Dumazet
2009-07-09 5:36 ` Eric Dumazet [this message]
2009-07-09 17:13 ` Paul E. McKenney
2009-07-09 20:50 ` Eric Dumazet
2009-07-12 3:27 ` David Miller
2009-07-12 7:07 ` Eric Dumazet
2009-07-15 12:28 ` [PATCH] net: nf_conntrack_alloc() should not use kmem_cache_zalloc() Eric Dumazet
2009-07-15 15:28 ` Patrick McHardy
2009-07-15 19:54 ` [PATCH] net: nf_conntrack_alloc() fixes Eric Dumazet
2009-07-16 9:13 ` [PATCH] net: sock_copy() fixes Eric Dumazet
2009-07-17 1:09 ` David Miller
2009-07-16 12:05 ` [PATCH] net: nf_conntrack_alloc() fixes Patrick McHardy
2009-07-08 17:02 ` [PATCH] net: sk_prot_alloc() should not blindly overwrite memory Tantilov, Emil S
2009-07-08 17:45 ` David Miller
2009-07-08 23:21 ` Eric Dumazet
2009-07-08 23:35 ` Tantilov, Emil S
2009-07-09 0:20 ` [PATCH] net: ip_push_pending_frames() fix Eric Dumazet
2009-07-09 14:32 ` Tantilov, Emil S
2009-07-09 14:38 ` Eric Dumazet
2009-07-12 3:27 ` David Miller
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