Skip to content

Commit

Permalink
ipv6: fix race condition regarding dst->expires and dst->from.
Browse files Browse the repository at this point in the history
Eric Dumazet wrote:
| Some strange crashes happen in rt6_check_expired(), with access
| to random addresses.
|
| At first glance, it looks like the RTF_EXPIRES and
| stuff added in commit 1716a96
| (ipv6: fix problem with expired dst cache)
| are racy : same dst could be manipulated at the same time
| on different cpus.
|
| At some point, our stack believes rt->dst.from contains a dst pointer,
| while its really a jiffie value (as rt->dst.expires shares the same area
| of memory)
|
| rt6_update_expires() should be fixed, or am I missing something ?
|
| CC Neil because of https://bugzilla.redhat.com/show_bug.cgi?id=892060

Because we do not have any locks for dst_entry, we cannot change
essential structure in the entry; e.g., we cannot change reference
to other entity.

To fix this issue, split 'from' and 'expires' field in dst_entry
out of union.  Once it is 'from' is assigned in the constructor,
keep the reference until the very last stage of the life time of
the object.

Of course, it is unsafe to change 'from', so make rt6_set_from simple
just for fresh entries.

Reported-by: Eric Dumazet <[email protected]>
Reported-by: Neil Horman <[email protected]>
CC: Gao Feng <[email protected]>
Signed-off-by: YOSHIFUJI Hideaki <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Reported-by: Steinar H. Gunderson <[email protected]>
Reviewed-by: Neil Horman <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
  • Loading branch information
yoshfuji authored and davem330 committed Feb 20, 2013
1 parent 68534c6 commit ecd9883
Showing 4 changed files with 18 additions and 38 deletions.
8 changes: 2 additions & 6 deletions include/net/dst.h
Original file line number Diff line number Diff line change
@@ -36,13 +36,9 @@ struct dst_entry {
struct net_device *dev;
struct dst_ops *ops;
unsigned long _metrics;
union {
unsigned long expires;
/* point to where the dst_entry copied from */
struct dst_entry *from;
};
unsigned long expires;
struct dst_entry *path;
void *__pad0;
struct dst_entry *from;
#ifdef CONFIG_XFRM
struct xfrm_state *xfrm;
#else
39 changes: 12 additions & 27 deletions include/net/ip6_fib.h
Original file line number Diff line number Diff line change
@@ -164,50 +164,35 @@ static inline struct inet6_dev *ip6_dst_idev(struct dst_entry *dst)

static inline void rt6_clean_expires(struct rt6_info *rt)
{
if (!(rt->rt6i_flags & RTF_EXPIRES) && rt->dst.from)
dst_release(rt->dst.from);

rt->rt6i_flags &= ~RTF_EXPIRES;
rt->dst.from = NULL;
}

static inline void rt6_set_expires(struct rt6_info *rt, unsigned long expires)
{
if (!(rt->rt6i_flags & RTF_EXPIRES) && rt->dst.from)
dst_release(rt->dst.from);

rt->rt6i_flags |= RTF_EXPIRES;
rt->dst.expires = expires;
rt->rt6i_flags |= RTF_EXPIRES;
}

static inline void rt6_update_expires(struct rt6_info *rt, int timeout)
static inline void rt6_update_expires(struct rt6_info *rt0, int timeout)
{
if (!(rt->rt6i_flags & RTF_EXPIRES)) {
if (rt->dst.from)
dst_release(rt->dst.from);
/* dst_set_expires relies on expires == 0
* if it has not been set previously.
*/
rt->dst.expires = 0;
}

dst_set_expires(&rt->dst, timeout);
rt->rt6i_flags |= RTF_EXPIRES;
struct rt6_info *rt;

for (rt = rt0; rt && !(rt->rt6i_flags & RTF_EXPIRES);
rt = (struct rt6_info *)rt->dst.from);
if (rt && rt != rt0)
rt0->dst.expires = rt->dst.expires;

dst_set_expires(&rt0->dst, timeout);
rt0->rt6i_flags |= RTF_EXPIRES;
}

static inline void rt6_set_from(struct rt6_info *rt, struct rt6_info *from)
{
struct dst_entry *new = (struct dst_entry *) from;

if (!(rt->rt6i_flags & RTF_EXPIRES) && rt->dst.from) {
if (new == rt->dst.from)
return;
dst_release(rt->dst.from);
}

rt->rt6i_flags &= ~RTF_EXPIRES;
rt->dst.from = new;
dst_hold(new);
rt->dst.from = new;
}

static inline void ip6_rt_put(struct rt6_info *rt)
1 change: 1 addition & 0 deletions net/core/dst.c
Original file line number Diff line number Diff line change
@@ -179,6 +179,7 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
dst_init_metrics(dst, dst_default_metrics, true);
dst->expires = 0UL;
dst->path = dst;
dst->from = NULL;
#ifdef CONFIG_XFRM
dst->xfrm = NULL;
#endif
8 changes: 3 additions & 5 deletions net/ipv6/route.c
Original file line number Diff line number Diff line change
@@ -287,6 +287,7 @@ static void ip6_dst_destroy(struct dst_entry *dst)
{
struct rt6_info *rt = (struct rt6_info *)dst;
struct inet6_dev *idev = rt->rt6i_idev;
struct dst_entry *from = dst->from;

if (!(rt->dst.flags & DST_HOST))
dst_destroy_metrics_generic(dst);
@@ -296,8 +297,8 @@ static void ip6_dst_destroy(struct dst_entry *dst)
in6_dev_put(idev);
}

if (!(rt->rt6i_flags & RTF_EXPIRES) && dst->from)
dst_release(dst->from);
dst->from = NULL;
dst_release(from);

if (rt6_has_peer(rt)) {
struct inet_peer *peer = rt6_peer_ptr(rt);
@@ -1010,7 +1011,6 @@ struct dst_entry *ip6_blackhole_route(struct net *net, struct dst_entry *dst_ori

rt->rt6i_gateway = ort->rt6i_gateway;
rt->rt6i_flags = ort->rt6i_flags;
rt6_clean_expires(rt);
rt->rt6i_metric = 0;

memcpy(&rt->rt6i_dst, &ort->rt6i_dst, sizeof(struct rt6key));
@@ -1784,8 +1784,6 @@ static struct rt6_info *ip6_rt_copy(struct rt6_info *ort,
if ((ort->rt6i_flags & (RTF_DEFAULT | RTF_ADDRCONF)) ==
(RTF_DEFAULT | RTF_ADDRCONF))
rt6_set_from(rt, ort);
else
rt6_clean_expires(rt);
rt->rt6i_metric = 0;

#ifdef CONFIG_IPV6_SUBTREES

0 comments on commit ecd9883

Please sign in to comment.