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Subject[PATCH 3.12 018/181] xfrm: fix race between netns cleanup and state expire notification
Date
From: Michal Kubecek <mkubecek@suse.cz>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit 21ee543edc0dea36ab58d24523fcd42b8a270df8 upstream.

The xfrm_user module registers its pernet init/exit after xfrm
itself so that its net exit function xfrm_user_net_exit() is
executed before xfrm_net_exit() which calls xfrm_state_fini() to
cleanup the SA's (xfrm states). This opens a window between
zeroing net->xfrm.nlsk pointer and deleting all xfrm_state
instances which may access it (via the timer). If an xfrm state
expires in this window, xfrm_exp_state_notify() will pass null
pointer as socket to nlmsg_multicast().

As the notifications are called inside rcu_read_lock() block, it
is sufficient to retrieve the nlsk socket with rcu_dereference()
and check the it for null.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
net/xfrm/xfrm_user.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 352dfa4c39ee..32a2dd39b785 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -930,6 +930,20 @@ static struct sk_buff *xfrm_state_netlink(struct sk_buff *in_skb,
return skb;
}

+/* A wrapper for nlmsg_multicast() checking that nlsk is still available.
+ * Must be called with RCU read lock.
+ */
+static inline int xfrm_nlmsg_multicast(struct net *net, struct sk_buff *skb,
+ u32 pid, unsigned int group)
+{
+ struct sock *nlsk = rcu_dereference(net->xfrm.nlsk);
+
+ if (nlsk)
+ return nlmsg_multicast(nlsk, skb, pid, group, GFP_ATOMIC);
+ else
+ return -1;
+}
+
static inline size_t xfrm_spdinfo_msgsize(void)
{
return NLMSG_ALIGN(4)
@@ -2253,7 +2267,7 @@ static int xfrm_send_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
if (build_migrate(skb, m, num_migrate, k, sel, dir, type) < 0)
BUG();

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_MIGRATE, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_MIGRATE);
}
#else
static int xfrm_send_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
@@ -2440,7 +2454,7 @@ static int xfrm_exp_state_notify(struct xfrm_state *x, const struct km_event *c)
return -EMSGSIZE;
}

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_EXPIRE, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_EXPIRE);
}

static int xfrm_aevent_state_notify(struct xfrm_state *x, const struct km_event *c)
@@ -2455,7 +2469,7 @@ static int xfrm_aevent_state_notify(struct xfrm_state *x, const struct km_event
if (build_aevent(skb, x, c) < 0)
BUG();

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_AEVENTS, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_AEVENTS);
}

static int xfrm_notify_sa_flush(const struct km_event *c)
@@ -2481,7 +2495,7 @@ static int xfrm_notify_sa_flush(const struct km_event *c)

nlmsg_end(skb, nlh);

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_SA, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_SA);
}

static inline size_t xfrm_sa_len(struct xfrm_state *x)
@@ -2568,7 +2582,7 @@ static int xfrm_notify_sa(struct xfrm_state *x, const struct km_event *c)

nlmsg_end(skb, nlh);

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_SA, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_SA);

out_free_skb:
kfree_skb(skb);
@@ -2659,7 +2673,7 @@ static int xfrm_send_acquire(struct xfrm_state *x, struct xfrm_tmpl *xt,
if (build_acquire(skb, x, xt, xp) < 0)
BUG();

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_ACQUIRE, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_ACQUIRE);
}

/* User gives us xfrm_user_policy_info followed by an array of 0
@@ -2773,7 +2787,7 @@ static int xfrm_exp_policy_notify(struct xfrm_policy *xp, int dir, const struct
if (build_polexpire(skb, xp, dir, c) < 0)
BUG();

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_EXPIRE, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_EXPIRE);
}

static int xfrm_notify_policy(struct xfrm_policy *xp, int dir, const struct km_event *c)
@@ -2835,7 +2849,7 @@ static int xfrm_notify_policy(struct xfrm_policy *xp, int dir, const struct km_e

nlmsg_end(skb, nlh);

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_POLICY, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_POLICY);

out_free_skb:
kfree_skb(skb);
@@ -2863,7 +2877,7 @@ static int xfrm_notify_policy_flush(const struct km_event *c)

nlmsg_end(skb, nlh);

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_POLICY, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_POLICY);

out_free_skb:
kfree_skb(skb);
@@ -2932,7 +2946,7 @@ static int xfrm_send_report(struct net *net, u8 proto,
if (build_report(skb, proto, sel, addr) < 0)
BUG();

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_REPORT, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_REPORT);
}

static inline size_t xfrm_mapping_msgsize(void)
@@ -2984,7 +2998,7 @@ static int xfrm_send_mapping(struct xfrm_state *x, xfrm_address_t *ipaddr,
if (build_mapping(skb, x, ipaddr, sport) < 0)
BUG();

- return nlmsg_multicast(net->xfrm.nlsk, skb, 0, XFRMNLGRP_MAPPING, GFP_ATOMIC);
+ return xfrm_nlmsg_multicast(net, skb, 0, XFRMNLGRP_MAPPING);
}

static struct xfrm_mgr netlink_mgr = {
--
2.0.0


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