x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 750 insertions, 0 deletions

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
new file mode 100644
index 000000000..c790d2f49
--- /dev/null
+++ b/net/ipv4/ip_fragment.c
@@ -0,0 +1,750 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * INET		An implementation of the TCP/IP protocol suite for the LINUX
+ *		operating system.  INET is implemented using the  BSD Socket
+ *		interface as the means of communication with the user level.
+ *
+ *		The IP fragmentation functionality.
+ *
+ * Authors:	Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
+ *		Alan Cox <alan@lxorguk.ukuu.org.uk>
+ *
+ * Fixes:
+ *		Alan Cox	:	Split from ip.c , see ip_input.c for history.
+ *		David S. Miller :	Begin massive cleanup...
+ *		Andi Kleen	:	Add sysctls.
+ *		xxxx		:	Overlapfrag bug.
+ *		Ultima          :       ip_expire() kernel panic.
+ *		Bill Hawes	:	Frag accounting and evictor fixes.
+ *		John McDonald	:	0 length frag bug.
+ *		Alexey Kuznetsov:	SMP races, threading, cleanup.
+ *		Patrick McHardy :	LRU queue of frag heads for evictor.
+ */
+
+#define pr_fmt(fmt) "IPv4: " fmt
+
+#include <linux/compiler.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/mm.h>
+#include <linux/jiffies.h>
+#include <linux/skbuff.h>
+#include <linux/list.h>
+#include <linux/ip.h>
+#include <linux/icmp.h>
+#include <linux/netdevice.h>
+#include <linux/jhash.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <net/route.h>
+#include <net/dst.h>
+#include <net/sock.h>
+#include <net/ip.h>
+#include <net/icmp.h>
+#include <net/checksum.h>
+#include <net/inetpeer.h>
+#include <net/inet_frag.h>
+#include <linux/tcp.h>
+#include <linux/udp.h>
+#include <linux/inet.h>
+#include <linux/netfilter_ipv4.h>
+#include <net/inet_ecn.h>
+#include <net/l3mdev.h>
+
+/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
+ * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
+ * as well. Or notify me, at least. --ANK
+ */
+static const char ip_frag_cache_name[] = "ip4-frags";
+
+/* Describe an entry in the "incomplete datagrams" queue. */
+struct ipq {
+	struct inet_frag_queue q;
+
+	u8		ecn; /* RFC3168 support */
+	u16		max_df_size; /* largest frag with DF set seen */
+	int             iif;
+	unsigned int    rid;
+	struct inet_peer *peer;
+};
+
+static u8 ip4_frag_ecn(u8 tos)
+{
+	return 1 << (tos & INET_ECN_MASK);
+}
+
+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,
+			 int *refs);
+
+
+static void ip4_frag_init(struct inet_frag_queue *q, const void *a)
+{
+	struct ipq *qp = container_of(q, struct ipq, q);
+	const struct frag_v4_compare_key *key = a;
+	struct net *net = q->fqdir->net;
+	struct inet_peer *p = NULL;
+
+	q->key.v4 = *key;
+	qp->ecn = 0;
+	if (q->fqdir->max_dist) {
+		rcu_read_lock();
+		p = inet_getpeer_v4(net->ipv4.peers, key->saddr, key->vif);
+		if (p && !refcount_inc_not_zero(&p->refcnt))
+			p = NULL;
+		rcu_read_unlock();
+	}
+	qp->peer = p;
+}
+
+static void ip4_frag_free(struct inet_frag_queue *q)
+{
+	struct ipq *qp;
+
+	qp = container_of(q, struct ipq, q);
+	if (qp->peer)
+		inet_putpeer(qp->peer);
+}
+
+static bool frag_expire_skip_icmp(u32 user)
+{
+	return user == IP_DEFRAG_AF_PACKET ||
+	       ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_IN,
+					 __IP_DEFRAG_CONNTRACK_IN_END) ||
+	       ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_BRIDGE_IN,
+					 __IP_DEFRAG_CONNTRACK_BRIDGE_IN);
+}
+
+/*
+ * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
+ */
+static void ip_expire(struct timer_list *t)
+{
+	enum skb_drop_reason reason = SKB_DROP_REASON_FRAG_REASM_TIMEOUT;
+	struct inet_frag_queue *frag = timer_container_of(frag, t, timer);
+	const struct iphdr *iph;
+	struct sk_buff *head = NULL;
+	struct net *net;
+	struct ipq *qp;
+	int refs = 1;
+
+	qp = container_of(frag, struct ipq, q);
+	net = qp->q.fqdir->net;
+
+	rcu_read_lock();
+	spin_lock(&qp->q.lock);
+
+	if (qp->q.flags & INET_FRAG_COMPLETE)
+		goto out;
+
+	qp->q.flags |= INET_FRAG_DROP;
+	inet_frag_kill(&qp->q, &refs);
+
+	/* Paired with WRITE_ONCE() in fqdir_pre_exit(). */
+	if (READ_ONCE(qp->q.fqdir->dead)) {
+		inet_frag_queue_flush(&qp->q, 0);
+		goto out;
+	}
+
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMTIMEOUT);
+
+	if (!(qp->q.flags & INET_FRAG_FIRST_IN))
+		goto out;
+
+	/* sk_buff::dev and sk_buff::rbnode are unionized. So we
+	 * pull the head out of the tree in order to be able to
+	 * deal with head->dev.
+	 */
+	head = inet_frag_pull_head(&qp->q);
+	if (!head)
+		goto out;
+	head->dev = dev_get_by_index_rcu(net, qp->iif);
+	if (!head->dev)
+		goto out;
+
+
+	/* skb has no dst, perform route lookup again */
+	iph = ip_hdr(head);
+	reason = ip_route_input_noref(head, iph->daddr, iph->saddr,
+				      ip4h_dscp(iph), head->dev);
+	if (reason)
+		goto out;
+
+	/* Only an end host needs to send an ICMP
+	 * "Fragment Reassembly Timeout" message, per RFC792.
+	 */
+	reason = SKB_DROP_REASON_FRAG_REASM_TIMEOUT;
+	if (frag_expire_skip_icmp(qp->q.key.v4.user) &&
+	    (skb_rtable(head)->rt_type != RTN_LOCAL))
+		goto out;
+
+	spin_unlock(&qp->q.lock);
+	icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
+	goto out_rcu_unlock;
+
+out:
+	spin_unlock(&qp->q.lock);
+out_rcu_unlock:
+	rcu_read_unlock();
+	kfree_skb_reason(head, reason);
+	inet_frag_putn(&qp->q, refs);
+}
+
+/* Find the correct entry in the "incomplete datagrams" queue for
+ * this IP datagram, and create new one, if nothing is found.
+ */
+static struct ipq *ip_find(struct net *net, struct iphdr *iph,
+			   u32 user, int vif)
+{
+	struct frag_v4_compare_key key = {
+		.saddr = iph->saddr,
+		.daddr = iph->daddr,
+		.user = user,
+		.vif = vif,
+		.id = iph->id,
+		.protocol = iph->protocol,
+	};
+	struct inet_frag_queue *q;
+
+	q = inet_frag_find(net->ipv4.fqdir, &key);
+	if (!q)
+		return NULL;
+
+	return container_of(q, struct ipq, q);
+}
+
+/* Is the fragment too far ahead to be part of ipq? */
+static int ip_frag_too_far(struct ipq *qp)
+{
+	struct inet_peer *peer = qp->peer;
+	unsigned int max = qp->q.fqdir->max_dist;
+	unsigned int start, end;
+
+	int rc;
+
+	if (!peer || !max)
+		return 0;
+
+	start = qp->rid;
+	end = atomic_inc_return(&peer->rid);
+	qp->rid = end;
+
+	rc = qp->q.fragments_tail && (end - start) > max;
+
+	if (rc)
+		__IP_INC_STATS(qp->q.fqdir->net, IPSTATS_MIB_REASMFAILS);
+
+	return rc;
+}
+
+static int ip_frag_reinit(struct ipq *qp)
+{
+	if (!mod_timer_pending(&qp->q.timer, jiffies + qp->q.fqdir->timeout))
+		return -ETIMEDOUT;
+
+	inet_frag_queue_flush(&qp->q, SKB_DROP_REASON_FRAG_TOO_FAR);
+
+	qp->q.flags = 0;
+	qp->q.len = 0;
+	qp->q.meat = 0;
+	qp->iif = 0;
+	qp->ecn = 0;
+
+	return 0;
+}
+
+/* Add new segment to existing queue. */
+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;
+	struct sk_buff *prev_tail;
+	struct net_device *dev;
+	unsigned int fragsize;
+	int err = -ENOENT;
+	SKB_DR(reason);
+	u8 ecn;
+
+	/* If reassembly is already done, @skb must be a duplicate frag. */
+	if (qp->q.flags & INET_FRAG_COMPLETE) {
+		SKB_DR_SET(reason, DUP_FRAG);
+		goto err;
+	}
+
+	if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
+	    unlikely(ip_frag_too_far(qp)) &&
+	    unlikely(err = ip_frag_reinit(qp))) {
+		inet_frag_kill(&qp->q, refs);
+		goto err;
+	}
+
+	ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
+	offset = ntohs(ip_hdr(skb)->frag_off);
+	flags = offset & ~IP_OFFSET;
+	offset &= IP_OFFSET;
+	offset <<= 3;		/* offset is in 8-byte chunks */
+	ihl = ip_hdrlen(skb);
+
+	/* Determine the position of this fragment. */
+	end = offset + skb->len - skb_network_offset(skb) - ihl;
+	err = -EINVAL;
+
+	/* Is this the final fragment? */
+	if ((flags & IP_MF) == 0) {
+		/* If we already have some bits beyond end
+		 * or have different end, the segment is corrupted.
+		 */
+		if (end < qp->q.len ||
+		    ((qp->q.flags & INET_FRAG_LAST_IN) && end != qp->q.len))
+			goto discard_qp;
+		qp->q.flags |= INET_FRAG_LAST_IN;
+		qp->q.len = end;
+	} else {
+		if (end&7) {
+			end &= ~7;
+			if (skb->ip_summed != CHECKSUM_UNNECESSARY)
+				skb->ip_summed = CHECKSUM_NONE;
+		}
+		if (end > qp->q.len) {
+			/* Some bits beyond end -> corruption. */
+			if (qp->q.flags & INET_FRAG_LAST_IN)
+				goto discard_qp;
+			qp->q.len = end;
+		}
+	}
+	if (end == offset)
+		goto discard_qp;
+
+	err = -ENOMEM;
+	if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
+		goto discard_qp;
+
+	err = pskb_trim_rcsum(skb, end - offset);
+	if (err)
+		goto discard_qp;
+
+	/* Note : skb->rbnode and skb->dev share the same location. */
+	dev = skb->dev;
+	/* Makes sure compiler wont do silly aliasing games */
+	barrier();
+
+	prev_tail = qp->q.fragments_tail;
+	err = inet_frag_queue_insert(&qp->q, skb, offset, end);
+	if (err)
+		goto insert_error;
+
+	if (dev)
+		qp->iif = dev->ifindex;
+
+	qp->q.stamp = skb->tstamp;
+	qp->q.tstamp_type = skb->tstamp_type;
+	qp->q.meat += skb->len;
+	qp->ecn |= ecn;
+	add_frag_mem_limit(qp->q.fqdir, skb->truesize);
+	if (offset == 0)
+		qp->q.flags |= INET_FRAG_FIRST_IN;
+
+	fragsize = skb->len + ihl;
+
+	if (fragsize > qp->q.max_size)
+		qp->q.max_size = fragsize;
+
+	if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
+	    fragsize > qp->max_df_size)
+		qp->max_df_size = fragsize;
+
+	if (qp->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
+	    qp->q.meat == qp->q.len) {
+		unsigned long orefdst = skb->_skb_refdst;
+
+		skb->_skb_refdst = 0UL;
+		err = ip_frag_reasm(qp, skb, prev_tail, dev, refs);
+		skb->_skb_refdst = orefdst;
+		if (err)
+			inet_frag_kill(&qp->q, refs);
+		return err;
+	}
+
+	skb_dst_drop(skb);
+	skb_orphan(skb);
+	return -EINPROGRESS;
+
+insert_error:
+	if (err == IPFRAG_DUP) {
+		SKB_DR_SET(reason, DUP_FRAG);
+		err = -EINVAL;
+		goto err;
+	}
+	err = -EINVAL;
+	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
+discard_qp:
+	inet_frag_kill(&qp->q, refs);
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
+err:
+	kfree_skb_reason(skb, reason);
+	return err;
+}
+
+static bool ip_frag_coalesce_ok(const struct ipq *qp)
+{
+	return qp->q.key.v4.user == IP_DEFRAG_LOCAL_DELIVER;
+}
+
+/* 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,
+			 int *refs)
+{
+	struct net *net = qp->q.fqdir->net;
+	struct iphdr *iph;
+	void *reasm_data;
+	int len, err;
+	u8 ecn;
+
+	inet_frag_kill(&qp->q, refs);
+
+	ecn = ip_frag_ecn_table[qp->ecn];
+	if (unlikely(ecn == 0xff)) {
+		err = -EINVAL;
+		goto out_fail;
+	}
+
+	/* Make the one we just received the head. */
+	reasm_data = inet_frag_reasm_prepare(&qp->q, skb, prev_tail);
+	if (!reasm_data)
+		goto out_nomem;
+
+	len = ip_hdrlen(skb) + qp->q.len;
+	err = -E2BIG;
+	if (len > 65535)
+		goto out_oversize;
+
+	inet_frag_reasm_finish(&qp->q, skb, reasm_data,
+			       ip_frag_coalesce_ok(qp));
+
+	skb->dev = dev;
+	IPCB(skb)->frag_max_size = max(qp->max_df_size, qp->q.max_size);
+
+	iph = ip_hdr(skb);
+	iph->tot_len = htons(len);
+	iph->tos |= ecn;
+
+	/* When we set IP_DF on a refragmented skb we must also force a
+	 * call to ip_fragment to avoid forwarding a DF-skb of size s while
+	 * original sender only sent fragments of size f (where f < s).
+	 *
+	 * We only set DF/IPSKB_FRAG_PMTU if such DF fragment was the largest
+	 * frag seen to avoid sending tiny DF-fragments in case skb was built
+	 * from one very small df-fragment and one large non-df frag.
+	 */
+	if (qp->max_df_size == qp->q.max_size) {
+		IPCB(skb)->flags |= IPSKB_FRAG_PMTU;
+		iph->frag_off = htons(IP_DF);
+	} else {
+		iph->frag_off = 0;
+	}
+
+	ip_send_check(iph);
+
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMOKS);
+	qp->q.rb_fragments = RB_ROOT;
+	qp->q.fragments_tail = NULL;
+	qp->q.last_run_head = NULL;
+	return 0;
+
+out_nomem:
+	net_dbg_ratelimited("queue_glue: no memory for gluing queue %p\n", qp);
+	err = -ENOMEM;
+	goto out_fail;
+out_oversize:
+	net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->q.key.v4.saddr);
+out_fail:
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
+	return err;
+}
+
+/* Process an incoming IP datagram fragment. */
+int ip_defrag(struct net *net, struct sk_buff *skb, u32 user)
+{
+	struct net_device *dev;
+	struct ipq *qp;
+	int vif;
+
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMREQDS);
+
+	/* Lookup (or create) queue header */
+	rcu_read_lock();
+	dev = skb->dev ? : skb_dst_dev_rcu(skb);
+	vif = l3mdev_master_ifindex_rcu(dev);
+	qp = ip_find(net, ip_hdr(skb), user, vif);
+	if (qp) {
+		int ret, refs = 0;
+
+		spin_lock(&qp->q.lock);
+
+		ret = ip_frag_queue(qp, skb, &refs);
+
+		spin_unlock(&qp->q.lock);
+		rcu_read_unlock();
+		inet_frag_putn(&qp->q, refs);
+		return ret;
+	}
+	rcu_read_unlock();
+
+	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
+	kfree_skb(skb);
+	return -ENOMEM;
+}
+EXPORT_SYMBOL(ip_defrag);
+
+struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
+{
+	struct iphdr iph;
+	int netoff;
+	u32 len;
+
+	if (skb->protocol != htons(ETH_P_IP))
+		return skb;
+
+	netoff = skb_network_offset(skb);
+
+	if (skb_copy_bits(skb, netoff, &iph, sizeof(iph)) < 0)
+		return skb;
+
+	if (iph.ihl < 5 || iph.version != 4)
+		return skb;
+
+	len = ntohs(iph.tot_len);
+	if (skb->len < netoff + len || len < (iph.ihl * 4))
+		return skb;
+
+	if (ip_is_fragment(&iph)) {
+		skb = skb_share_check(skb, GFP_ATOMIC);
+		if (skb) {
+			if (!pskb_may_pull(skb, netoff + iph.ihl * 4)) {
+				kfree_skb(skb);
+				return NULL;
+			}
+			if (pskb_trim_rcsum(skb, netoff + len)) {
+				kfree_skb(skb);
+				return NULL;
+			}
+			memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
+			if (ip_defrag(net, skb, user))
+				return NULL;
+			skb_clear_hash(skb);
+		}
+	}
+	return skb;
+}
+EXPORT_SYMBOL(ip_check_defrag);
+
+#ifdef CONFIG_SYSCTL
+static int dist_min;
+
+static struct ctl_table ip4_frags_ns_ctl_table[] = {
+	{
+		.procname	= "ipfrag_high_thresh",
+		.maxlen		= sizeof(unsigned long),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
+	{
+		.procname	= "ipfrag_low_thresh",
+		.maxlen		= sizeof(unsigned long),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
+	{
+		.procname	= "ipfrag_time",
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_jiffies,
+	},
+	{
+		.procname	= "ipfrag_max_dist",
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &dist_min,
+	},
+};
+
+/* secret interval has been deprecated */
+static int ip4_frags_secret_interval_unused;
+static struct ctl_table ip4_frags_ctl_table[] = {
+	{
+		.procname	= "ipfrag_secret_interval",
+		.data		= &ip4_frags_secret_interval_unused,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_jiffies,
+	},
+};
+
+static int __net_init ip4_frags_ns_ctl_register(struct net *net)
+{
+	struct ctl_table *table;
+	struct ctl_table_header *hdr;
+
+	table = ip4_frags_ns_ctl_table;
+	if (!net_eq(net, &init_net)) {
+		table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
+		if (!table)
+			goto err_alloc;
+
+	}
+	table[0].data	= &net->ipv4.fqdir->high_thresh;
+	table[0].extra1	= &net->ipv4.fqdir->low_thresh;
+	table[1].data	= &net->ipv4.fqdir->low_thresh;
+	table[1].extra2	= &net->ipv4.fqdir->high_thresh;
+	table[2].data	= &net->ipv4.fqdir->timeout;
+	table[3].data	= &net->ipv4.fqdir->max_dist;
+
+	hdr = register_net_sysctl_sz(net, "net/ipv4", table,
+				     ARRAY_SIZE(ip4_frags_ns_ctl_table));
+	if (!hdr)
+		goto err_reg;
+
+	net->ipv4.frags_hdr = hdr;
+	return 0;
+
+err_reg:
+	if (!net_eq(net, &init_net))
+		kfree(table);
+err_alloc:
+	return -ENOMEM;
+}
+
+static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
+{
+	const struct ctl_table *table;
+
+	table = net->ipv4.frags_hdr->ctl_table_arg;
+	unregister_net_sysctl_table(net->ipv4.frags_hdr);
+	kfree(table);
+}
+
+static void __init ip4_frags_ctl_register(void)
+{
+	register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
+}
+#else
+static int ip4_frags_ns_ctl_register(struct net *net)
+{
+	return 0;
+}
+
+static void ip4_frags_ns_ctl_unregister(struct net *net)
+{
+}
+
+static void __init ip4_frags_ctl_register(void)
+{
+}
+#endif
+
+static int __net_init ipv4_frags_init_net(struct net *net)
+{
+	int res;
+
+	res = fqdir_init(&net->ipv4.fqdir, &ip4_frags, net);
+	if (res < 0)
+		return res;
+	/* Fragment cache limits.
+	 *
+	 * The fragment memory accounting code, (tries to) account for
+	 * the real memory usage, by measuring both the size of frag
+	 * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
+	 * and the SKB's truesize.
+	 *
+	 * A 64K fragment consumes 129736 bytes (44*2944)+200
+	 * (1500 truesize == 2944, sizeof(struct ipq) == 200)
+	 *
+	 * We will commit 4MB at one time. Should we cross that limit
+	 * we will prune down to 3MB, making room for approx 8 big 64K
+	 * fragments 8x128k.
+	 */
+	net->ipv4.fqdir->high_thresh = 4 * 1024 * 1024;
+	net->ipv4.fqdir->low_thresh  = 3 * 1024 * 1024;
+	/*
+	 * Important NOTE! Fragment queue must be destroyed before MSL expires.
+	 * RFC791 is wrong proposing to prolongate timer each fragment arrival
+	 * by TTL.
+	 */
+	net->ipv4.fqdir->timeout = IP_FRAG_TIME;
+
+	net->ipv4.fqdir->max_dist = 64;
+
+	res = ip4_frags_ns_ctl_register(net);
+	if (res < 0)
+		fqdir_exit(net->ipv4.fqdir);
+	return res;
+}
+
+static void __net_exit ipv4_frags_pre_exit_net(struct net *net)
+{
+	fqdir_pre_exit(net->ipv4.fqdir);
+}
+
+static void __net_exit ipv4_frags_exit_net(struct net *net)
+{
+	ip4_frags_ns_ctl_unregister(net);
+	fqdir_exit(net->ipv4.fqdir);
+}
+
+static struct pernet_operations ip4_frags_ops = {
+	.init		= ipv4_frags_init_net,
+	.pre_exit	= ipv4_frags_pre_exit_net,
+	.exit		= ipv4_frags_exit_net,
+};
+
+
+static u32 ip4_key_hashfn(const void *data, u32 len, u32 seed)
+{
+	return jhash2(data,
+		      sizeof(struct frag_v4_compare_key) / sizeof(u32), seed);
+}
+
+static u32 ip4_obj_hashfn(const void *data, u32 len, u32 seed)
+{
+	const struct inet_frag_queue *fq = data;
+
+	return jhash2((const u32 *)&fq->key.v4,
+		      sizeof(struct frag_v4_compare_key) / sizeof(u32), seed);
+}
+
+static int ip4_obj_cmpfn(struct rhashtable_compare_arg *arg, const void *ptr)
+{
+	const struct frag_v4_compare_key *key = arg->key;
+	const struct inet_frag_queue *fq = ptr;
+
+	return !!memcmp(&fq->key, key, sizeof(*key));
+}
+
+static const struct rhashtable_params ip4_rhash_params = {
+	.head_offset		= offsetof(struct inet_frag_queue, node),
+	.key_offset		= offsetof(struct inet_frag_queue, key),
+	.key_len		= sizeof(struct frag_v4_compare_key),
+	.hashfn			= ip4_key_hashfn,
+	.obj_hashfn		= ip4_obj_hashfn,
+	.obj_cmpfn		= ip4_obj_cmpfn,
+	.automatic_shrinking	= true,
+};
+
+void __init ipfrag_init(void)
+{
+	ip4_frags.constructor = ip4_frag_init;
+	ip4_frags.destructor = ip4_frag_free;
+	ip4_frags.qsize = sizeof(struct ipq);
+	ip4_frags.frag_expire = ip_expire;
+	ip4_frags.frags_cache_name = ip_frag_cache_name;
+	ip4_frags.rhash_params = ip4_rhash_params;
+	if (inet_frags_init(&ip4_frags))
+		panic("IP: failed to allocate ip4_frags cache\n");
+	ip4_frags_ctl_register();
+	register_pernet_subsys(&ip4_frags_ops);
+}