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Message-ID: <1506010546.29839.148.camel@edumazet-glaptop3.roam.corp.google.com>
Date: Thu, 21 Sep 2017 09:15:46 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Paweł Staszewski <pstaszewski@...are.pl>
Cc: Wei Wang <weiwan@...gle.com>, Cong Wang <xiyou.wangcong@...il.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net] net: prevent dst uses after free
From: Eric Dumazet <edumazet@...gle.com>
In linux-4.13, Wei worked hard to convert dst to a traditional
refcounted model, removing GC.
We now want to make sure a dst refcount can not transition from 0 back
to 1.
The problem here is that input path attached a not refcounted dst to an
skb. Then later, because packet is forwarded and hits skb_dst_force()
before exiting RCU section, we might try to take a refcount on one dst
that is about to be freed, if another cpu saw 1 -> 0 transition in
dst_release() and queued the dst for freeing after one RCU grace period.
Lets unify skb_dst_force() and skb_dst_force_safe(), since we should
always perform the complete check against dst refcount, and not assume
it is not zero.
Bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=197005
[ 989.919496] skb_dst_force+0x32/0x34
[ 989.919498] __dev_queue_xmit+0x1ad/0x482
[ 989.919501] ? eth_header+0x28/0xc6
[ 989.919502] dev_queue_xmit+0xb/0xd
[ 989.919504] neigh_connected_output+0x9b/0xb4
[ 989.919507] ip_finish_output2+0x234/0x294
[ 989.919509] ? ipt_do_table+0x369/0x388
[ 989.919510] ip_finish_output+0x12c/0x13f
[ 989.919512] ip_output+0x53/0x87
[ 989.919513] ip_forward_finish+0x53/0x5a
[ 989.919515] ip_forward+0x2cb/0x3e6
[ 989.919516] ? pskb_trim_rcsum.part.9+0x4b/0x4b
[ 989.919518] ip_rcv_finish+0x2e2/0x321
[ 989.919519] ip_rcv+0x26f/0x2eb
[ 989.919522] ? vlan_do_receive+0x4f/0x289
[ 989.919523] __netif_receive_skb_core+0x467/0x50b
[ 989.919526] ? tcp_gro_receive+0x239/0x239
[ 989.919529] ? inet_gro_receive+0x226/0x238
[ 989.919530] __netif_receive_skb+0x4d/0x5f
[ 989.919532] netif_receive_skb_internal+0x5c/0xaf
[ 989.919533] napi_gro_receive+0x45/0x81
[ 989.919536] ixgbe_poll+0xc8a/0xf09
[ 989.919539] ? kmem_cache_free_bulk+0x1b6/0x1f7
[ 989.919540] net_rx_action+0xf4/0x266
[ 989.919543] __do_softirq+0xa8/0x19d
[ 989.919545] irq_exit+0x5d/0x6b
[ 989.919546] do_IRQ+0x9c/0xb5
[ 989.919548] common_interrupt+0x93/0x93
[ 989.919548] </IRQ>
Similarly dst_clone() can use dst_hold() helper to have additional
debugging, as a follow up to commit 44ebe79149ff ("net: add debug
atomic_inc_not_zero() in dst_hold()")
In net-next we will convert dst atomic_t to refcount_t for peace of
mind.
Fixes: a4c2fd7f7891 ("net: remove DST_NOCACHE flag")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Wei Wang <weiwan@...gle.com>
Reported-by: Paweł Staszewski <pstaszewski@...are.pl>
Bisected-by: Paweł Staszewski <pstaszewski@...are.pl>
---
include/net/dst.h | 22 ++++------------------
include/net/route.h | 2 +-
include/net/sock.h | 2 +-
3 files changed, 6 insertions(+), 20 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index 93568bd0a3520bb7402f04d90cf04ac99c81cfbe..06a6765da074449e6f1fe42ee05e711e898ad372 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -271,7 +271,7 @@ static inline void dst_use_noref(struct dst_entry *dst, unsigned long time)
static inline struct dst_entry *dst_clone(struct dst_entry *dst)
{
if (dst)
- atomic_inc(&dst->__refcnt);
+ dst_hold(dst);
return dst;
}
@@ -311,21 +311,6 @@ static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb
__skb_dst_copy(nskb, oskb->_skb_refdst);
}
-/**
- * skb_dst_force - makes sure skb dst is refcounted
- * @skb: buffer
- *
- * If dst is not yet refcounted, let's do it
- */
-static inline void skb_dst_force(struct sk_buff *skb)
-{
- if (skb_dst_is_noref(skb)) {
- WARN_ON(!rcu_read_lock_held());
- skb->_skb_refdst &= ~SKB_DST_NOREF;
- dst_clone(skb_dst(skb));
- }
-}
-
/**
* dst_hold_safe - Take a reference on a dst if possible
* @dst: pointer to dst entry
@@ -339,16 +324,17 @@ static inline bool dst_hold_safe(struct dst_entry *dst)
}
/**
- * skb_dst_force_safe - makes sure skb dst is refcounted
+ * skb_dst_force - makes sure skb dst is refcounted
* @skb: buffer
*
* If dst is not yet refcounted and not destroyed, grab a ref on it.
*/
-static inline void skb_dst_force_safe(struct sk_buff *skb)
+static inline void skb_dst_force(struct sk_buff *skb)
{
if (skb_dst_is_noref(skb)) {
struct dst_entry *dst = skb_dst(skb);
+ WARN_ON(!rcu_read_lock_held());
if (!dst_hold_safe(dst))
dst = NULL;
diff --git a/include/net/route.h b/include/net/route.h
index 1b09a9368c68d46f0c5ee8ce3cefe566000c1ec1..57dfc6850d378e4b96f13b140eef554d66c24cdf 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -190,7 +190,7 @@ static inline int ip_route_input(struct sk_buff *skb, __be32 dst, __be32 src,
rcu_read_lock();
err = ip_route_input_noref(skb, dst, src, tos, devin);
if (!err) {
- skb_dst_force_safe(skb);
+ skb_dst_force(skb);
if (!skb_dst(skb))
err = -EINVAL;
}
diff --git a/include/net/sock.h b/include/net/sock.h
index 03a362568357acc7278a318423dd3873103f90ca..a6b9a8d1a6df3f72df8f1aac0f577257fa6452d0 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -856,7 +856,7 @@ void sk_stream_write_space(struct sock *sk);
static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb)
{
/* dont let skb dst not refcounted, we are going to leave rcu lock */
- skb_dst_force_safe(skb);
+ skb_dst_force(skb);
if (!sk->sk_backlog.tail)
sk->sk_backlog.head = skb;
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