[PATCH net v3] 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 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); + version = nla_get_u32(info->attrs[GTPA_VERSION]);

family = nla_get_u8_default(info->attrs[GTPA_FAMILY], AF_INET); @@ -2134,6 +2140,8 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info) if (!info->attrs[GTPA_VERSION]) return -EINVAL;

+ mutex_lock(&gtp_pdp_lock); + rcu_read_lock();

pctx = gtp_find_pdp(sock_net(skb->sk), info->attrs); @@ -2154,6 +2162,7 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)

out_unlock: rcu_read_unlock(); + mutex_unlock(&gtp_pdp_lock); return err; }