[PATCH 6.12 11/77] inet: frags: change inet_frag_kill() to defer refcount updates

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

------------------

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit eb0dfc0ef195a04e519b15d73cf25d8c25ee8df7 ]

In the following patch, we no longer assume inet_frag_kill()
callers own a reference.

Consuming two refcounts from inet_frag_kill() would lead in UAF.

Propagate the pointer to the refs that will be consumed later
by the final inet_frag_putn() call.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250312082250.1803501-4-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Stable-dep-of: 653d7ddf6cba ("inet: frags: publish queues before arming timer")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/net/inet_frag.h                 |    2 +-
 include/net/ipv6_frag.h                 |    2 +-
 net/ieee802154/6lowpan/reassembly.c     |   17 ++++++++++-------
 net/ipv4/inet_fragment.c                |   12 +++++++-----
 net/ipv4/ip_fragment.c                  |   30 ++++++++++++------------------
 net/ipv6/netfilter/nf_conntrack_reasm.c |   21 ++++++++++++---------
 net/ipv6/reassembly.c                   |   18 ++++++++++--------
 7 files changed, 53 insertions(+), 49 deletions(-)

--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -126,7 +126,7 @@ int fqdir_init(struct fqdir **fqdirp, st
 void fqdir_pre_exit(struct fqdir *fqdir);
 void fqdir_exit(struct fqdir *fqdir);
 
-void inet_frag_kill(struct inet_frag_queue *q);
+void inet_frag_kill(struct inet_frag_queue *q, int *refs);
 void inet_frag_destroy(struct inet_frag_queue *q);
 struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key);
 
--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h
@@ -75,7 +75,7 @@ ip6frag_expire_frag_queue(struct net *ne
 		goto out;
 
 	fq->q.flags |= INET_FRAG_DROP;
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, &refs);
 
 	/* Paired with the WRITE_ONCE() in fqdir_pre_exit(). */
 	if (READ_ONCE(fq->q.fqdir->dead)) {
--- a/net/ieee802154/6lowpan/reassembly.c
+++ b/net/ieee802154/6lowpan/reassembly.c
@@ -31,7 +31,8 @@ static const char lowpan_frags_cache_nam
 static struct inet_frags lowpan_frags;
 
 static int lowpan_frag_reasm(struct lowpan_frag_queue *fq, struct sk_buff *skb,
-			     struct sk_buff *prev,  struct net_device *ldev);
+			     struct sk_buff *prev, struct net_device *ldev,
+			     int *refs);
 
 static void lowpan_frag_init(struct inet_frag_queue *q, const void *a)
 {
@@ -54,7 +55,7 @@ static void lowpan_frag_expire(struct ti
 	if (fq->q.flags & INET_FRAG_COMPLETE)
 		goto out;
 
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, &refs);
 out:
 	spin_unlock(&fq->q.lock);
 	inet_frag_putn(&fq->q, refs);
@@ -83,7 +84,8 @@ fq_find(struct net *net, const struct lo
 }
 
 static int lowpan_frag_queue(struct lowpan_frag_queue *fq,
-			     struct sk_buff *skb, u8 frag_type)
+			     struct sk_buff *skb, u8 frag_type,
+			     int *refs)
 {
 	struct sk_buff *prev_tail;
 	struct net_device *ldev;
@@ -144,7 +146,7 @@ static int lowpan_frag_queue(struct lowp
 		unsigned long orefdst = skb->_skb_refdst;
 
 		skb->_skb_refdst = 0UL;
-		res = lowpan_frag_reasm(fq, skb, prev_tail, ldev);
+		res = lowpan_frag_reasm(fq, skb, prev_tail, ldev, refs);
 		skb->_skb_refdst = orefdst;
 		return res;
 	}
@@ -163,11 +165,12 @@ err:
  *	the last and the first frames arrived and all the bits are here.
  */
 static int lowpan_frag_reasm(struct lowpan_frag_queue *fq, struct sk_buff *skb,
-			     struct sk_buff *prev_tail, struct net_device *ldev)
+			     struct sk_buff *prev_tail, struct net_device *ldev,
+			     int *refs)
 {
 	void *reasm_data;
 
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 
 	reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
 	if (!reasm_data)
@@ -306,7 +309,7 @@ int lowpan_frag_rcv(struct sk_buff *skb,
 		int ret, refs = 1;
 
 		spin_lock(&fq->q.lock);
-		ret = lowpan_frag_queue(fq, skb, frag_type);
+		ret = lowpan_frag_queue(fq, skb, frag_type, &refs);
 		spin_unlock(&fq->q.lock);
 
 		inet_frag_putn(&fq->q, refs);
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -260,10 +260,10 @@ void fqdir_exit(struct fqdir *fqdir)
 }
 EXPORT_SYMBOL(fqdir_exit);
 
-void inet_frag_kill(struct inet_frag_queue *fq)
+void inet_frag_kill(struct inet_frag_queue *fq, int *refs)
 {
 	if (del_timer(&fq->timer))
-		refcount_dec(&fq->refcnt);
+		(*refs)++;
 
 	if (!(fq->flags & INET_FRAG_COMPLETE)) {
 		struct fqdir *fqdir = fq->fqdir;
@@ -278,7 +278,7 @@ void inet_frag_kill(struct inet_frag_que
 		if (!READ_ONCE(fqdir->dead)) {
 			rhashtable_remove_fast(&fqdir->rhashtable, &fq->node,
 					       fqdir->f->rhash_params);
-			refcount_dec(&fq->refcnt);
+			(*refs)++;
 		} else {
 			fq->flags |= INET_FRAG_HASH_DEAD;
 		}
@@ -397,9 +397,11 @@ static struct inet_frag_queue *inet_frag
 	*prev = rhashtable_lookup_get_insert_key(&fqdir->rhashtable, &q->key,
 						 &q->node, f->rhash_params);
 	if (*prev) {
+		int refs = 2;
+
 		q->flags |= INET_FRAG_COMPLETE;
-		inet_frag_kill(q);
-		inet_frag_destroy(q);
+		inet_frag_kill(q, &refs);
+		inet_frag_putn(q, refs);
 		return NULL;
 	}
 	return q;
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -76,7 +76,8 @@ static u8 ip4_frag_ecn(u8 tos)
 static struct inet_frags ip4_frags;
 
 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
-			 struct sk_buff *prev_tail, struct net_device *dev);
+			 struct sk_buff *prev_tail, struct net_device *dev,
+			 int *refs);
 
 
 static void ip4_frag_init(struct inet_frag_queue *q, const void *a)
@@ -107,14 +108,6 @@ static void ip4_frag_free(struct inet_fr
 		inet_putpeer(qp->peer);
 }
 
-/* Kill ipq entry. It is not destroyed immediately,
- * because caller (and someone more) holds reference count.
- */
-static void ipq_kill(struct ipq *ipq)
-{
-	inet_frag_kill(&ipq->q);
-}
-
 static bool frag_expire_skip_icmp(u32 user)
 {
 	return user == IP_DEFRAG_AF_PACKET ||
@@ -147,7 +140,7 @@ static void ip_expire(struct timer_list
 		goto out;
 
 	qp->q.flags |= INET_FRAG_DROP;
-	ipq_kill(qp);
+	inet_frag_kill(&qp->q, &refs);
 
 	/* Paired with WRITE_ONCE() in fqdir_pre_exit(). */
 	if (READ_ONCE(qp->q.fqdir->dead)) {
@@ -265,7 +258,7 @@ static int ip_frag_reinit(struct ipq *qp
 }
 
 /* Add new segment to existing queue. */
-static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
+static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb, int *refs)
 {
 	struct net *net = qp->q.fqdir->net;
 	int ihl, end, flags, offset;
@@ -285,7 +278,7 @@ static int ip_frag_queue(struct ipq *qp,
 	if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
 	    unlikely(ip_frag_too_far(qp)) &&
 	    unlikely(err = ip_frag_reinit(qp))) {
-		ipq_kill(qp);
+		inet_frag_kill(&qp->q, refs);
 		goto err;
 	}
 
@@ -369,10 +362,10 @@ static int ip_frag_queue(struct ipq *qp,
 		unsigned long orefdst = skb->_skb_refdst;
 
 		skb->_skb_refdst = 0UL;
-		err = ip_frag_reasm(qp, skb, prev_tail, dev);
+		err = ip_frag_reasm(qp, skb, prev_tail, dev, refs);
 		skb->_skb_refdst = orefdst;
 		if (err)
-			inet_frag_kill(&qp->q);
+			inet_frag_kill(&qp->q, refs);
 		return err;
 	}
 
@@ -389,7 +382,7 @@ insert_error:
 	err = -EINVAL;
 	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
 discard_qp:
-	inet_frag_kill(&qp->q);
+	inet_frag_kill(&qp->q, refs);
 	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
 err:
 	kfree_skb_reason(skb, reason);
@@ -403,7 +396,8 @@ static bool ip_frag_coalesce_ok(const st
 
 /* Build a new IP datagram from all its fragments. */
 static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
-			 struct sk_buff *prev_tail, struct net_device *dev)
+			 struct sk_buff *prev_tail, struct net_device *dev,
+			 int *refs)
 {
 	struct net *net = qp->q.fqdir->net;
 	struct iphdr *iph;
@@ -411,7 +405,7 @@ static int ip_frag_reasm(struct ipq *qp,
 	int len, err;
 	u8 ecn;
 
-	ipq_kill(qp);
+	inet_frag_kill(&qp->q, refs);
 
 	ecn = ip_frag_ecn_table[qp->ecn];
 	if (unlikely(ecn == 0xff)) {
@@ -489,7 +483,7 @@ int ip_defrag(struct net *net, struct sk
 
 		spin_lock(&qp->q.lock);
 
-		ret = ip_frag_queue(qp, skb);
+		ret = ip_frag_queue(qp, skb, &refs);
 
 		spin_unlock(&qp->q.lock);
 		inet_frag_putn(&qp->q, refs);
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -123,7 +123,8 @@ static void __net_exit nf_ct_frags6_sysc
 #endif
 
 static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
-			     struct sk_buff *prev_tail, struct net_device *dev);
+			     struct sk_buff *prev_tail, struct net_device *dev,
+			     int *refs);
 
 static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
 {
@@ -167,7 +168,8 @@ static struct frag_queue *fq_find(struct
 
 
 static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
-			     const struct frag_hdr *fhdr, int nhoff)
+			     const struct frag_hdr *fhdr, int nhoff,
+			     int *refs)
 {
 	unsigned int payload_len;
 	struct net_device *dev;
@@ -221,7 +223,7 @@ static int nf_ct_frag6_queue(struct frag
 			 * this case. -DaveM
 			 */
 			pr_debug("end of fragment not rounded to 8 bytes.\n");
-			inet_frag_kill(&fq->q);
+			inet_frag_kill(&fq->q, refs);
 			return -EPROTO;
 		}
 		if (end > fq->q.len) {
@@ -287,7 +289,7 @@ static int nf_ct_frag6_queue(struct frag
 		unsigned long orefdst = skb->_skb_refdst;
 
 		skb->_skb_refdst = 0UL;
-		err = nf_ct_frag6_reasm(fq, skb, prev, dev);
+		err = nf_ct_frag6_reasm(fq, skb, prev, dev, refs);
 		skb->_skb_refdst = orefdst;
 
 		/* After queue has assumed skb ownership, only 0 or
@@ -301,7 +303,7 @@ static int nf_ct_frag6_queue(struct frag
 	return -EINPROGRESS;
 
 insert_error:
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 err:
 	skb_dst_drop(skb);
 	return -EINVAL;
@@ -315,13 +317,14 @@ err:
  *	the last and the first frames arrived and all the bits are here.
  */
 static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
-			     struct sk_buff *prev_tail, struct net_device *dev)
+			     struct sk_buff *prev_tail, struct net_device *dev,
+			     int *refs)
 {
 	void *reasm_data;
 	int payload_len;
 	u8 ecn;
 
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 
 	ecn = ip_frag_ecn_table[fq->ecn];
 	if (unlikely(ecn == 0xff))
@@ -373,7 +376,7 @@ static int nf_ct_frag6_reasm(struct frag
 	return 0;
 
 err:
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 	return -EINVAL;
 }
 
@@ -484,7 +487,7 @@ int nf_ct_frag6_gather(struct net *net,
 
 	spin_lock_bh(&fq->q.lock);
 
-	ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff);
+	ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff, &refs);
 	if (ret == -EPROTO) {
 		skb->transport_header = savethdr;
 		ret = 0;
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -68,7 +68,8 @@ static u8 ip6_frag_ecn(const struct ipv6
 static struct inet_frags ip6_frags;
 
 static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
-			  struct sk_buff *prev_tail, struct net_device *dev);
+			  struct sk_buff *prev_tail, struct net_device *dev,
+			  int *refs);
 
 static void ip6_frag_expire(struct timer_list *t)
 {
@@ -105,7 +106,7 @@ fq_find(struct net *net, __be32 id, cons
 
 static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 			  struct frag_hdr *fhdr, int nhoff,
-			  u32 *prob_offset)
+			  u32 *prob_offset, int *refs)
 {
 	struct net *net = dev_net(skb_dst(skb)->dev);
 	int offset, end, fragsize;
@@ -220,7 +221,7 @@ static int ip6_frag_queue(struct frag_qu
 		unsigned long orefdst = skb->_skb_refdst;
 
 		skb->_skb_refdst = 0UL;
-		err = ip6_frag_reasm(fq, skb, prev_tail, dev);
+		err = ip6_frag_reasm(fq, skb, prev_tail, dev, refs);
 		skb->_skb_refdst = orefdst;
 		return err;
 	}
@@ -238,7 +239,7 @@ insert_error:
 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
 			IPSTATS_MIB_REASM_OVERLAPS);
 discard_fq:
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
 			IPSTATS_MIB_REASMFAILS);
 err:
@@ -254,7 +255,8 @@ err:
  *	the last and the first frames arrived and all the bits are here.
  */
 static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *skb,
-			  struct sk_buff *prev_tail, struct net_device *dev)
+			  struct sk_buff *prev_tail, struct net_device *dev,
+			  int *refs)
 {
 	struct net *net = fq->q.fqdir->net;
 	unsigned int nhoff;
@@ -262,7 +264,7 @@ static int ip6_frag_reasm(struct frag_qu
 	int payload_len;
 	u8 ecn;
 
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 
 	ecn = ip_frag_ecn_table[fq->ecn];
 	if (unlikely(ecn == 0xff))
@@ -320,7 +322,7 @@ out_fail:
 	rcu_read_lock();
 	__IP6_INC_STATS(net, __in6_dev_stats_get(dev, skb), IPSTATS_MIB_REASMFAILS);
 	rcu_read_unlock();
-	inet_frag_kill(&fq->q);
+	inet_frag_kill(&fq->q, refs);
 	return -1;
 }
 
@@ -386,7 +388,7 @@ static int ipv6_frag_rcv(struct sk_buff
 
 		fq->iif = iif;
 		ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff,
-				     &prob_offset);
+				     &prob_offset, &refs);
 
 		spin_unlock(&fq->q.lock);
 		inet_frag_putn(&fq->q, refs);