Re: [PATCH net v3] gtp: serialize PDP context updates

From: Qing Ming a0yami@mailbox.org Date: Tue, 11 Aug 2026 10:20:12 +0800

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 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 PDP context updates with a mutex shared by gtp_pdp_add(), gtp_genl_del_pdp(), and gtp_dellink().

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)") Assisted-by: Codex:gpt-5 Signed-off-by: Qing Ming a0yami@mailbox.org

---

v3:

• Rebase onto net/main.

v2: https://lore.kernel.org/netdev/20260808124322.5800-1-a0yami@mailbox.org/

• Use a dedicated mutex instead of RTNL.
• Protect PDP add, delete, and link teardown with the same mutex.

drivers/net/gtp.c | 9 +++++++++ 1 file changed, 9 insertions(+)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c index 9a12cc53da00..8ee516debeed 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;

@@ -1555,9 +1557,11 @@ 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);

@@ -1833,6 +1837,8 @@ static struct pdp_ctx *gtp_pdp_add(struct gtp_dev *gtp, struct sock *sk, __be32 ms_addr; int family;

• guard(mutex)(&gtp_pdp_lock);

Please use the plain mutex_lock() / mutex_unlock().

---8<--- $ cat Documentation/process/maintainer-netdev.rst ... Using device-managed and cleanup.h constructs ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Netdev remains skeptical about promises of all "auto-cleanup" APIs, including even ``devm_`` helpers, historically. They are not the preferred style of implementation, merely an acceptable one.

Use of ``guard()`` is discouraged within any function longer than 20 lines, ``scoped_guard()`` is considered more readable. Using normal lock/unlock is still (weakly) preferred. ---8<---