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Sat, 07 Nov 2026 08:27:22 -0800 (PST) Received: from xploitoverload ([2409:40c1:6412:e5b:5516:cd42:6c8f:c918]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36fa9aea75fsm29025370eec.15.2026.11.07.08.27.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Nov 2026 08:27:21 -0800 (PST) From: Kalpesh Solanki To: willemdebruijn.kernel@gmail.com, jasowangio@gmail.com, alex.aring@gmail.com, stefan@datenfreihafen.org, miquel.raynal@bootlin.com, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com Cc: andrew+netdev@lunn.ch, linux-wpan@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+9ea34da5ca6100593c90@syzkaller.appspotmail.com, Kalpesh Solanki Subject: [PATCH net v3] tun: disallow setting IEEE 802.15.4 and 6LoWPAN link types via TUNSETLINK Date: Sat, 7 Nov 2026 21:56:49 +0530 Message-ID: <20261107162649.282982-1-skalpesh942@gmail.com> X-Mailer: git-send-email 2.53.0 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A userspace application can set the link type of a TUN/TAP interface to ARPHRD_IEEE802154, ARPHRD_IEEE802154_MONITOR, or ARPHRD_6LOWPAN via ioctl(fd, TUNSETLINK, arg) because tun_get_addr_len() explicitly recognized these types. However, TUN devices cannot function as genuine IEEE 802.15.4 or 6LoWPAN interfaces: 1. They lack wpan_phy, channels, PAN IDs, and MLME operations, and tun never initializes dev->ieee802154_ptr or dev->ml_priv. When an unprivileged user creates a TUN interface in a user+net namespace, changes its link type to ARPHRD_IEEE802154, and issues a netlink dump request (such as IEEE802154_LLSEC_LIST_KEY), ieee802154_llsec_dump_table() unconditionally dereferences dev->ieee802154_ptr / ieee802154_mlme_ops(dev), triggering a supervisor null-pointer dereference / general protection fault. Similar dereferences occur across net/ieee802154/nl-phy.c (ieee802154_del_iface) and net/ieee802154/socket.c. 2. Similarly, the 6LoWPAN subsystem assumes via lowpan_dev(dev) that netdev_priv(dev) is struct lowpan_dev. On a TUN device, netdev_priv(dev) is struct tun_struct. On netdev events (such as NETDEV_DOWN in net/6lowpan/core.c:lowpan_device_event), it clears bits in lowpan_dev(dev)->ctx.table flags, which corrupts private memory inside tun_struct. Rather than scattering checks across subsystems, fix the issue at the source: disallow setting ARPHRD_IEEE802154, ARPHRD_IEEE802154_MONITOR, and ARPHRD_6LOWPAN via TUNSETLINK by returning -EINVAL. Fixes: cca8ea3b05c9 ("net: tun: set tun->dev->addr_len during TUNSETLINK processing") Reported-by: syzbot+9ea34da5ca6100593c90@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9ea34da5ca6100593c90 Signed-off-by: Kalpesh Solanki --- v2 -> v3: - Include ARPHRD_6LOWPAN alongside ARPHRD_IEEE802154 as agreed with Willem de Bruijn, preventing Sashiko AI flags and addressing the underlying lowpan_dev(dev) memory corruption. - Minimize code churn as advised by Willem de Bruijn: drop unrelated USHRT_MAX check and preserve tun_get_addr_len(), headers, and existing block indentation. - Fresh standalone thread as advised by Jakub Kicinski. - Link to v1 and v2 discussion: https://lore.kernel.org/all/20261101092219.1278751-1-skalpesh942@gmail.com/ v1 -> v2: - Instead of adding NULL checks in net/ieee802154/nl-mac.c, disallow setting ARPHRD_IEEE802154 and ARPHRD_IEEE802154_MONITOR link types via TUNSETLINK in drivers/net/tun.c, as discussed with Andrew Lunn and identified in Sashiko bot review. Virtual IEEE 802.15.4 interfaces are properly provided by mac802154_hwsim and fakelb; TUN devices cannot function as genuine 802.15.4 radios and lack private 802.15.4 contexts. - Add an explicit bounds check (arg > USHRT_MAX) to prevent integer truncation bypasses when casting 64-bit ioctl arg to 16-bit dev->type. - Remove ARPHRD_IEEE802154 and ARPHRD_IEEE802154_MONITOR from tun_get_addr_len() and drop unused header. drivers/net/tun.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index dcec7311e60..05eb28578b8 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -3362,6 +3362,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, netif_info(tun, drv, tun->dev, "Linktype set failed because interface is up\n"); ret = -EBUSY; + } else if (arg == ARPHRD_IEEE802154 || + arg == ARPHRD_IEEE802154_MONITOR || + arg == ARPHRD_6LOWPAN) { + ret = -EINVAL; } else { ret = call_netdevice_notifiers(NETDEV_PRE_TYPE_CHANGE, tun->dev); -- 2.53.0