Re: [PATCH net v4] gtp: serialize PDP context updates

On Fri, Aug 14, 2026 at 11:15:26AM +0800, Qing Ming wrote:

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: stable@vger.kernel.org Assisted-by: Codex:gpt-5 Signed-off-by: Qing Ming a0yami@mailbox.org

---

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/20260811022012.5416-1-a0yami@mailbox.org/ 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)

This does not look fine, it should protect the entire section where this pctx object is used.

• 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);

Same here.

• 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