[PATCH net v4] gtp: serialize PDP context updates

PDP contexts can be deleted through GTP_CMD_DELPDP or while the GTP
network device is being unregistered. The latter is serialized by RTNL,
but the generic-netlink delete path only holds RCU.

Running both paths concurrently can therefore make both paths delete the
same PDP context. The issue was found through static analysis and
reproduced on a KASAN-enabled kernel by a simple two-thread program
racing GTP_CMD_DELPDP against RTM_DELLINK:

  Oops: general protection fault, probably for non-canonical address
  KASAN: maybe wild-memory-access in range
         [0xdead000000000120-0xdead000000000127]
  RIP: gtp_genl_del_pdp+0x1c1/0x420 [gtp]
  RBP: dead000000000122

The second deletion dereferenced the poisoned hlist pprev pointer.

Serialize gtp_pdp_add(), gtp_genl_del_pdp(), and gtp_dellink() with a
shared mutex. With this change, the same reproducer completed 50 races
on a KASAN- and lockdep-enabled kernel without a KASAN report, oops, or
lockdep warning.

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Cc: [email protected]
Assisted-by: Codex:gpt-5
Signed-off-by: Qing Ming <[email protected]>
---
v4:
- Replace guard() with plain mutex_lock()/mutex_unlock() in the
  GTP_CMD_NEWPDP path.
- Narrow the RCU read-side section in gtp_genl_del_pdp() to
  gtp_find_pdp(); gtp_find_dev() uses dev_get_by_index_rcu().
- Add mutex-aware lockdep conditions to the shared PDP lookup helpers.

v3: https://lore.kernel.org/netdev/[email protected]/
 drivers/net/gtp.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 9a12cc53da00..ea83a6b6aa1a 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -12,6 +12,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/skbuff.h>
 #include <linux/udp.h>
 #include <linux/rculist.h>
@@ -108,6 +109,7 @@ struct gtp_net {
 };
 
 static u32 gtp_h_initval;
+static DEFINE_MUTEX(gtp_pdp_lock);
 
 static struct genl_family gtp_genl_family;
 
@@ -151,7 +153,8 @@ static struct pdp_ctx *gtp0_pdp_find(struct gtp_dev *gtp, u64 tid, u16 family)
 
 	head = &gtp->tid_hash[gtp0_hashfn(tid) % gtp->hash_size];
 
-	hlist_for_each_entry_rcu(pdp, head, hlist_tid) {
+	hlist_for_each_entry_rcu(pdp, head, hlist_tid,
+				 lockdep_is_held(&gtp_pdp_lock)) {
 		if (pdp->af == family &&
 		    pdp->gtp_version == GTP_V0 &&
 		    pdp->u.v0.tid == tid)
@@ -168,7 +171,8 @@ static struct pdp_ctx *gtp1_pdp_find(struct gtp_dev *gtp, u32 tid, u16 family)
 
 	head = &gtp->tid_hash[gtp1u_hashfn(tid) % gtp->hash_size];
 
-	hlist_for_each_entry_rcu(pdp, head, hlist_tid) {
+	hlist_for_each_entry_rcu(pdp, head, hlist_tid,
+				 lockdep_is_held(&gtp_pdp_lock)) {
 		if (pdp->af == family &&
 		    pdp->gtp_version == GTP_V1 &&
 		    pdp->u.v1.i_tei == tid)
@@ -185,7 +189,8 @@ static struct pdp_ctx *ipv4_pdp_find(struct gtp_dev *gtp, __be32 ms_addr)
 
 	head = &gtp->addr_hash[ipv4_hashfn(ms_addr) % gtp->hash_size];
 
-	hlist_for_each_entry_rcu(pdp, head, hlist_addr) {
+	hlist_for_each_entry_rcu(pdp, head, hlist_addr,
+				 lockdep_is_held(&gtp_pdp_lock)) {
 		if (pdp->af == AF_INET &&
 		    pdp->ms.addr.s_addr == ms_addr)
 			return pdp;
@@ -220,7 +225,8 @@ static struct pdp_ctx *ipv6_pdp_find(struct gtp_dev *gtp,
 
 	head = &gtp->addr_hash[ipv6_hashfn(ms_addr) % gtp->hash_size];
 
-	hlist_for_each_entry_rcu(pdp, head, hlist_addr) {
+	hlist_for_each_entry_rcu(pdp, head, hlist_addr,
+				 lockdep_is_held(&gtp_pdp_lock)) {
 		if (pdp->af == AF_INET6 &&
 		    ipv6_pdp_addr_equal(&pdp->ms.addr6, ms_addr))
 			return pdp;
@@ -1555,9 +1561,11 @@ static void gtp_dellink(struct net_device *dev, struct list_head *head)
 	struct pdp_ctx *pctx;
 	int i;
 
+	mutex_lock(&gtp_pdp_lock);
 	for (i = 0; i < gtp->hash_size; i++)
 		hlist_for_each_entry_safe(pctx, next, &gtp->tid_hash[i], hlist_tid)
 			pdp_context_delete(pctx);
+	mutex_unlock(&gtp_pdp_lock);
 
 	list_del(&gtp->list);
 	unregister_netdevice_queue(dev, head);
@@ -2053,7 +2061,9 @@ static int gtp_genl_new_pdp(struct sk_buff *skb, struct genl_info *info)
 		goto out_unlock;
 	}
 
+	mutex_lock(&gtp_pdp_lock);
 	pctx = gtp_pdp_add(gtp, sk, info);
+	mutex_unlock(&gtp_pdp_lock);
 	if (IS_ERR(pctx)) {
 		err = PTR_ERR(pctx);
 	} else {
@@ -2134,9 +2144,12 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
 	if (!info->attrs[GTPA_VERSION])
 		return -EINVAL;
 
-	rcu_read_lock();
+	mutex_lock(&gtp_pdp_lock);
 
+	/* gtp_find_dev() uses dev_get_by_index_rcu(). */
+	rcu_read_lock();
 	pctx = gtp_find_pdp(sock_net(skb->sk), info->attrs);
+	rcu_read_unlock();
 	if (IS_ERR(pctx)) {
 		err = PTR_ERR(pctx);
 		goto out_unlock;
@@ -2153,7 +2166,7 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
 	pdp_context_delete(pctx);
 
 out_unlock:
-	rcu_read_unlock();
+	mutex_unlock(&gtp_pdp_lock);
 	return err;
 }
 

base-commit: 24ef02f934eeb48830cff6b739abc3c62b1d107b
-- 
2.53.0