net/ipv6: Another followup to the fib6_info change

PATCH In review David Ahern 2 participants 9 messages Apr 20, 2018 – Apr 21, 2018

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David Ahern

author

2018-04-20 22:38 UTC #0 lore raw

cover net/ipv6: Another followup to the fib6_info change

Last one - for this week.

Patches 1, 2 and 7 are more cleanup patches - removing dead code, moving code from a header to near its single caller, and updating function name.

Patches 3-5 do some refactoring leading up to patch 6 which fixes a NULL dereference. I have only managed to trigger a panic once, so I can not definitively confirm it addresses the problem but it seems pretty clear that it is a race on removing a 'from' reference on an rt6_info and another path using that 'from' value to do cookie checking.

David Ahern (7):
net/ipv6: Clean up rt expires helpers
net/ipv6: Rename rt6_get_cookie_safe
net/ipv6: Move rcu_read_lock to callers of ip6_rt_cache_alloc net/ipv6: Move rcu locking to callers of fib6_get_cookie_safe net/ipv6: Move release of fib6_info from pcpu routes to helper net/ipv6: Make from in rt6_info rcu protected net/ipv6: Remove unncessary check on f6i in fib6_check

 include/net/ip6_fib.h |  41 +++++------------
 net/ipv6/ip6_fib.c    |  45 ++++++++++--------
 net/ipv6/ip6_output.c |   9 +++-
 net/ipv6/route.c      | 124 ++++++++++++++++++++++++++++++++++++--------------
 4 files changed, 136 insertions(+), 83 deletions(-)

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #1 lore raw

PATCH 1/7 net/ipv6: Clean up rt expires helpers

rt6_clean_expires and rt6_set_expires are no longer used. Removed them. rt6_update_expires has 1 caller in route.c, so move it from the header.

Signed-off-by David Ahern <[email protected]>

---
 include/net/ip6_fib.h | 21 ---------------------
 net/ipv6/route.c      |  9 +++++++++
 2 files changed, 9 insertions(+), 21 deletions(-)

include/net/ip6_fib.h +0 ~~-21~~

index 642211174692..327a74cd6a0d 100644
@@ -223,27 +223,6 @@ static inline bool fib6_check_expired(const struct fib6_info *f6i)
 	return false;
 }
 
-static inline void rt6_clean_expires(struct rt6_info *rt)
-{
-	rt->rt6i_flags &= ~RTF_EXPIRES;
-	rt->dst.expires = 0;
-}
-
-static inline void rt6_set_expires(struct rt6_info *rt, unsigned long expires)
-{
-	rt->dst.expires = expires;
-	rt->rt6i_flags |= RTF_EXPIRES;
-}
-
-static inline void rt6_update_expires(struct rt6_info *rt0, int timeout)
-{
-	if (!(rt0->rt6i_flags & RTF_EXPIRES) && rt0->from)
-		rt0->dst.expires = rt0->from->expires;
-
-	dst_set_expires(&rt0->dst, timeout);
-	rt0->rt6i_flags |= RTF_EXPIRES;
-}
-
 /* Function to safely get fn->sernum for passed in rt
  * and store result in passed in cookie.
  * Return true if we can get cookie safely

net/ipv6/route.c +9 -0

index 884d9cee790f..062dd4d8232c 100644
@@ -2221,6 +2221,15 @@ static void ip6_link_failure(struct sk_buff *skb)
 	}
 }
 
+static void rt6_update_expires(struct rt6_info *rt0, int timeout)
+{
+	if (!(rt0->rt6i_flags & RTF_EXPIRES) && rt0->from)
+		rt0->dst.expires = rt0->from->expires;
+
+	dst_set_expires(&rt0->dst, timeout);
+	rt0->rt6i_flags |= RTF_EXPIRES;
+}
+
 static void rt6_do_update_pmtu(struct rt6_info *rt, u32 mtu)
 {
 	struct net *net = dev_net(rt->dst.dev);

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #2 lore raw

PATCH 2/7 net/ipv6: Rename rt6_get_cookie_safe

In reply to David Ahern

rt6_get_cookie_safe takes a fib6_info and checks the sernum of the node. Update the name to reflect its purpose.

Signed-off-by David Ahern <[email protected]>

---
 include/net/ip6_fib.h | 6 +++---
 net/ipv6/route.c      | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

include/net/ip6_fib.h +3 -3

index 327a74cd6a0d..dd1481ed8bdb 100644
@@ -228,8 +228,8 @@ static inline bool fib6_check_expired(const struct fib6_info *f6i)
  * Return true if we can get cookie safely
  * Return false if not
  */
-static inline bool rt6_get_cookie_safe(const struct fib6_info *f6i,
-				       u32 *cookie)
+static inline bool fib6_get_cookie_safe(const struct fib6_info *f6i,
+					u32 *cookie)
 {
 	struct fib6_node *fn;
 	bool status = false;

@@ -254,7 +254,7 @@ static inline u32 rt6_get_cookie(const struct rt6_info *rt)
 
 	if (rt->rt6i_flags & RTF_PCPU ||
 	    (unlikely(!list_empty(&rt->rt6i_uncached)) && rt->from))
-		rt6_get_cookie_safe(rt->from, &cookie);
+		fib6_get_cookie_safe(rt->from, &cookie);
 
 	return cookie;
 }

net/ipv6/route.c +2 -2

index 062dd4d8232c..2d6fcfe11c82 100644
@@ -2128,7 +2128,7 @@ static bool fib6_check(struct fib6_info *f6i, u32 cookie)
 {
 	u32 rt_cookie = 0;
 
-	if ((f6i && !rt6_get_cookie_safe(f6i, &rt_cookie)) ||
+	if ((f6i && !fib6_get_cookie_safe(f6i, &rt_cookie)) ||
 	     rt_cookie != cookie)
 		return false;

@@ -2142,7 +2142,7 @@ static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie)
 {
 	u32 rt_cookie = 0;
 
-	if ((rt->from && !rt6_get_cookie_safe(rt->from, &rt_cookie)) ||
+	if ((rt->from && !fib6_get_cookie_safe(rt->from, &rt_cookie)) ||
 	    rt_cookie != cookie)
 		return NULL;

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #3 lore raw

PATCH 3/7 net/ipv6: Move rcu_read_lock to callers of ip6_rt_cache_alloc

In reply to David Ahern

A later patch protects 'from' in rt6_info and this simplifies the locking needed by it.

With the move, the fib6_info_hold for the uncached_rt is no longer needed since the rcu_lock is still held.

Signed-off-by David Ahern <[email protected]>

---
 net/ipv6/route.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

net/ipv6/route.c +6 -7

index 2d6fcfe11c82..f8b22183b7fd 100644
@@ -1164,10 +1164,8 @@ static struct rt6_info *ip6_rt_cache_alloc(struct fib6_info *ort,
 	 *	Clone the route.
 	 */
 
-	rcu_read_lock();
 	dev = ip6_rt_get_dev_rcu(ort);
 	rt = ip6_dst_alloc(dev_net(dev), dev, 0);
-	rcu_read_unlock();
 	if (!rt)
 		return NULL;

@@ -1855,14 +1853,11 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
 		 * the daddr in the skb during the neighbor look-up is different
 		 * from the fl6->daddr used to look-up route here.
 		 */
-
 		struct rt6_info *uncached_rt;
 
-		fib6_info_hold(f6i);
-		rcu_read_unlock();
-
 		uncached_rt = ip6_rt_cache_alloc(f6i, &fl6->daddr, NULL);
-		fib6_info_release(f6i);
+
+		rcu_read_unlock();
 
 		if (uncached_rt) {
 			/* Uncached_rt's refcnt is taken during ip6_rt_cache_alloc()

@@ -2280,7 +2275,9 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
 	} else if (daddr) {
 		struct rt6_info *nrt6;
 
+		rcu_read_lock();
 		nrt6 = ip6_rt_cache_alloc(rt6->from, daddr, saddr);
+		rcu_read_unlock();
 		if (nrt6) {
 			rt6_do_update_pmtu(nrt6, mtu);
 			if (rt6_insert_exception(nrt6, rt6->from))

@@ -3299,7 +3296,9 @@ static void rt6_do_redirect(struct dst_entry *dst, struct sock *sk, struct sk_bu
 				     NEIGH_UPDATE_F_ISROUTER)),
 		     NDISC_REDIRECT, &ndopts);
 
+	rcu_read_lock();
 	nrt = ip6_rt_cache_alloc(rt->from, &msg->dest, NULL);
+	rcu_read_unlock();
 	if (!nrt)
 		goto out;

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #4 lore raw

PATCH 4/7 net/ipv6: Move rcu locking to callers of fib6_get_cookie_safe

In reply to David Ahern

A later patch protects 'from' in rt6_info and this simplifies the locking needed by it.

Signed-off-by David Ahern <[email protected]>

---
 include/net/ip6_fib.h |  6 ++++--
 net/ipv6/route.c      | 13 ++++++++++---
 2 files changed, 14 insertions(+), 5 deletions(-)

include/net/ip6_fib.h +4 -2

index dd1481ed8bdb..dc3505fb62b3 100644
@@ -234,7 +234,6 @@ static inline bool fib6_get_cookie_safe(const struct fib6_info *f6i,
 	struct fib6_node *fn;
 	bool status = false;
 
-	rcu_read_lock();
 	fn = rcu_dereference(f6i->fib6_node);
 
 	if (fn) {

@@ -244,7 +243,6 @@ static inline bool fib6_get_cookie_safe(const struct fib6_info *f6i,
 		status = true;
 	}
 
-	rcu_read_unlock();
 	return status;
 }

@@ -252,10 +250,14 @@ static inline u32 rt6_get_cookie(const struct rt6_info *rt)
 {
 	u32 cookie = 0;
 
+	rcu_read_lock();
+
 	if (rt->rt6i_flags & RTF_PCPU ||
 	    (unlikely(!list_empty(&rt->rt6i_uncached)) && rt->from))
 		fib6_get_cookie_safe(rt->from, &cookie);
 
+	rcu_read_unlock();
+
 	return cookie;
 }

net/ipv6/route.c +10 -3

index f8b22183b7fd..810a37ac043b 100644
@@ -2159,9 +2159,12 @@ static struct dst_entry *rt6_dst_from_check(struct rt6_info *rt, u32 cookie)
 
 static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
 {
+	struct dst_entry *dst_ret;
 	struct rt6_info *rt;
 
-	rt = (struct rt6_info *) dst;
+	rt = container_of(dst, struct rt6_info, dst);
+
+	rcu_read_lock();
 
 	/* All IPV6 dsts are created with ->obsolete set to the value
 	 * DST_OBSOLETE_FORCE_CHK which forces validation calls down

@@ -2170,9 +2173,13 @@ static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
 
 	if (rt->rt6i_flags & RTF_PCPU ||
 	    (unlikely(!list_empty(&rt->rt6i_uncached)) && rt->from))
-		return rt6_dst_from_check(rt, cookie);
+		dst_ret = rt6_dst_from_check(rt, cookie);
 	else
-		return rt6_check(rt, cookie);
+		dst_ret = rt6_check(rt, cookie);
+
+	rcu_read_unlock();
+
+	return dst_ret;
 }
 
 static struct dst_entry *ip6_negative_advice(struct dst_entry *dst)

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #5 lore raw

PATCH 5/7 net/ipv6: Move release of fib6_info from pcpu routes to helper

In reply to David Ahern

Code move only; no functional change intended.

Signed-off-by David Ahern <[email protected]>

---
 net/ipv6/ip6_fib.c | 41 +++++++++++++++++++++++------------------
 1 file changed, 23 insertions(+), 18 deletions(-)

net/ipv6/ip6_fib.c +23 ~~-18~~

index f936e91a8c65..64ca02b7745f 100644
@@ -860,6 +860,27 @@ static struct fib6_node *fib6_add_1(struct net *net,
 	return ln;
 }
 
+static void fib6_drop_pcpu_from(struct fib6_info *f6i,
+				const struct fib6_table *table)
+{
+	int cpu;
+
+	/* release the reference to this fib entry from
+	 * all of its cached pcpu routes
+	 */
+	for_each_possible_cpu(cpu) {
+		struct rt6_info **ppcpu_rt;
+		struct rt6_info *pcpu_rt;
+
+		ppcpu_rt = per_cpu_ptr(f6i->rt6i_pcpu, cpu);
+		pcpu_rt = *ppcpu_rt;
+		if (pcpu_rt) {
+			fib6_info_release(pcpu_rt->from);
+			pcpu_rt->from = NULL;
+		}
+	}
+}
+
 static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn,
 			  struct net *net)
 {

@@ -887,24 +908,8 @@ static void fib6_purge_rt(struct fib6_info *rt, struct fib6_node *fn,
 				    lockdep_is_held(&table->tb6_lock));
 		}
 
-		if (rt->rt6i_pcpu) {
-			int cpu;
-
-			/* release the reference to this fib entry from
-			 * all of its cached pcpu routes
-			 */
-			for_each_possible_cpu(cpu) {
-				struct rt6_info **ppcpu_rt;
-				struct rt6_info *pcpu_rt;
-
-				ppcpu_rt = per_cpu_ptr(rt->rt6i_pcpu, cpu);
-				pcpu_rt = *ppcpu_rt;
-				if (pcpu_rt) {
-					fib6_info_release(pcpu_rt->from);
-					pcpu_rt->from = NULL;
-				}
-			}
-		}
+		if (rt->rt6i_pcpu)
+			fib6_drop_pcpu_from(rt, table);
 	}
 }

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #6 lore raw

PATCH 6/7 net/ipv6: Make from in rt6_info rcu protected

In reply to David Ahern

When a dst entry is created from a fib entry, the 'from' in rt6_info is set to the fib entry. The 'from' reference is used most notably for cookie checking - making sure stale dst entries are updated if the fib entry is changed.

When a fib entry is deleted, the pcpu routes on it are walked releasing the fib6_info reference. This is needed for the fib6_info cleanup to happen and to make sure all device references are released in a timely manner.

There is a race window when a FIB entry is deleted and the 'from' on the pcpu route is dropped and the pcpu route hits a cookie check. Handle this race using rcu on from.

Signed-off-by David Ahern <[email protected]>

---
 include/net/ip6_fib.h | 10 +++---
 net/ipv6/ip6_fib.c    |  8 +++--
 net/ipv6/ip6_output.c |  9 +++--
 net/ipv6/route.c      | 96 ++++++++++++++++++++++++++++++++++++---------------
 4 files changed, 88 insertions(+), 35 deletions(-)

include/net/ip6_fib.h +6 -4

index dc3505fb62b3..1af450d4e923 100644
@@ -174,7 +174,7 @@ struct fib6_info {
 
 struct rt6_info {
 	struct dst_entry		dst;
-	struct fib6_info		*from;
+	struct fib6_info __rcu		*from;
 
 	struct rt6key			rt6i_dst;
 	struct rt6key			rt6i_src;

@@ -248,13 +248,15 @@ static inline bool fib6_get_cookie_safe(const struct fib6_info *f6i,
 
 static inline u32 rt6_get_cookie(const struct rt6_info *rt)
 {
+	struct fib6_info *from;
 	u32 cookie = 0;
 
 	rcu_read_lock();
 
-	if (rt->rt6i_flags & RTF_PCPU ||
-	    (unlikely(!list_empty(&rt->rt6i_uncached)) && rt->from))
-		fib6_get_cookie_safe(rt->from, &cookie);
+	from = rcu_dereference(rt->from);
+	if (from && (rt->rt6i_flags & RTF_PCPU ||
+	    unlikely(!list_empty(&rt->rt6i_uncached))))
+		fib6_get_cookie_safe(from, &cookie);
 
 	rcu_read_unlock();

net/ipv6/ip6_fib.c +6 -2

index 64ca02b7745f..6421c893466e 100644
@@ -875,8 +875,12 @@ static void fib6_drop_pcpu_from(struct fib6_info *f6i,
 		ppcpu_rt = per_cpu_ptr(f6i->rt6i_pcpu, cpu);
 		pcpu_rt = *ppcpu_rt;
 		if (pcpu_rt) {
-			fib6_info_release(pcpu_rt->from);
-			pcpu_rt->from = NULL;
+			struct fib6_info *from;
+
+			from = rcu_dereference_protected(pcpu_rt->from,
+					     lockdep_is_held(&table->tb6_lock));
+			rcu_assign_pointer(pcpu_rt->from, NULL);
+			fib6_info_release(from);
 		}
 	}
 }

net/ipv6/ip6_output.c +7 -2

index 3db47986ef38..6a477d54f8c7 100644
@@ -962,16 +962,21 @@ static int ip6_dst_lookup_tail(struct net *net, const struct sock *sk,
 	 * that's why we try it again later.
 	 */
 	if (ipv6_addr_any(&fl6->saddr) && (!*dst || !(*dst)->error)) {
+		struct fib6_info *from;
 		struct rt6_info *rt;
 		bool had_dst = *dst != NULL;
 
 		if (!had_dst)
 			*dst = ip6_route_output(net, sk, fl6);
 		rt = (*dst)->error ? NULL : (struct rt6_info *)*dst;
-		err = ip6_route_get_saddr(net, rt ? rt->from : NULL,
-					  &fl6->daddr,
+
+		rcu_read_lock();
+		from = rt ? rcu_dereference(rt->from) : NULL;
+		err = ip6_route_get_saddr(net, from, &fl6->daddr,
 					  sk ? inet6_sk(sk)->srcprefs : 0,
 					  &fl6->saddr);
+		rcu_read_unlock();
+
 		if (err)
 			goto out_err_release;

net/ipv6/route.c +69 ~~-27~~

221 lines not on this page · raw message

Signature · 1 line

2.11.0

David Ahern

author

2018-04-20 22:38 UTC #7 lore raw

PATCH 7/7 net/ipv6: Remove unncessary check on f6i in fib6_check

In reply to David Ahern

Dan reported an imbalance in fib6_check on use of f6i and checking whether it is null. Since fib6_check is only called if f6i is non-null, remove the unnecessary check.

Reported-by Dan Carpenter <[email protected]>

Signed-off-by David Ahern <[email protected]>

---
 net/ipv6/route.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

net/ipv6/route.c +1 -2

index 004d00fe2fe5..0407bbc5a028 100644
@@ -2130,8 +2130,7 @@ static bool fib6_check(struct fib6_info *f6i, u32 cookie)
 {
 	u32 rt_cookie = 0;
 
-	if ((f6i && !fib6_get_cookie_safe(f6i, &rt_cookie)) ||
-	     rt_cookie != cookie)
+	if (!fib6_get_cookie_safe(f6i, &rt_cookie) || rt_cookie != cookie)
 		return false;
 
 	if (fib6_check_expired(f6i))

Signature · 1 line

2.11.0

David Miller

maintainer

2018-04-21 20:06 UTC #8 lore raw

In reply to David Ahern

From: David Ahern <[email protected]>
Date: Fri, 20 Apr 2018 15:37:56 -0700

Quoted 6 lines

Last one - for this week.
Patches 1, 2 and 7 are more cleanup patches - removing dead code, moving code from a header to near its single caller, and updating function name.

Quoted 6 lines

Patches 3-5 do some refactoring leading up to patch 6 which fixes a NULL dereference. I have only managed to trigger a panic once, so I can not definitively confirm it addresses the problem but it seems pretty clear that it is a race on removing a 'from' reference on an rt6_info and another path using that 'from' value to do cookie checking.

Great work, series applied.