From 23dad2d088dfc82cae1f5a936f8ff7ffebb38dd9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 6 Jul 2026 16:35:17 +0000 Subject: [PATCH] tun: no longer rely on RTNL in tun_fill_info() Update tun_fill_info() to read device configuration fields (flags, owner, group, numqueues, numdisabled) locklessly using READ_ONCE(). Annotate all writes to these fields in the control paths with WRITE_ONCE() to prevent data races, as these fields can be modified concurrently via ioctls (TUNSETPERSIST, TUNSETOWNER, TUNSETGROUP, TUNSETIFF) or queue attaching/detaching. Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260706163517.2415530-1-edumazet@google.com Signed-off-by: Paolo Abeni --- drivers/net/tun.c | 60 ++++++++++++++++++++++-------------------- drivers/net/tun_vnet.h | 8 +++--- 2 files changed, 36 insertions(+), 32 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index ffbe6f13fb1f..9e2761887896 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -532,7 +532,7 @@ static void tun_disable_queue(struct tun_struct *tun, struct tun_file *tfile) { tfile->detached = tun; list_add_tail(&tfile->next, &tun->disabled); - ++tun->numdisabled; + WRITE_ONCE(tun->numdisabled, tun->numdisabled + 1); } static struct tun_struct *tun_enable_queue(struct tun_file *tfile) @@ -541,7 +541,7 @@ static struct tun_struct *tun_enable_queue(struct tun_file *tfile) tfile->detached = NULL; list_del_init(&tfile->next); - --tun->numdisabled; + WRITE_ONCE(tun->numdisabled, tun->numdisabled - 1); return tun; } @@ -600,7 +600,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean) rcu_assign_pointer(tun->tfiles[tun->numqueues - 1], NULL); - --tun->numqueues; + WRITE_ONCE(tun->numqueues, tun->numqueues - 1); if (clean) { RCU_INIT_POINTER(tfile->tun, NULL); sock_put(&tfile->sk); @@ -663,7 +663,7 @@ static void tun_detach_all(struct net_device *dev) tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN; tfile->socket.sk->sk_data_ready(tfile->socket.sk); RCU_INIT_POINTER(tfile->tun, NULL); - --tun->numqueues; + WRITE_ONCE(tun->numqueues, tun->numqueues - 1); } list_for_each_entry(tfile, &tun->disabled, next) { tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN; @@ -786,7 +786,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file, if (publish_tun) rcu_assign_pointer(tfile->tun, tun); rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); - tun->numqueues++; + WRITE_ONCE(tun->numqueues, tun->numqueues + 1); tun_set_real_num_queues(tun); out: return err; @@ -2370,32 +2370,36 @@ static size_t tun_get_size(const struct net_device *dev) static int tun_fill_info(struct sk_buff *skb, const struct net_device *dev) { - struct tun_struct *tun = netdev_priv(dev); + const struct tun_struct *tun = netdev_priv(dev); + unsigned int flags = READ_ONCE(tun->flags); + kuid_t owner = READ_ONCE(tun->owner); + kgid_t group = READ_ONCE(tun->group); - if (nla_put_u8(skb, IFLA_TUN_TYPE, tun->flags & TUN_TYPE_MASK)) + if (nla_put_u8(skb, IFLA_TUN_TYPE, flags & TUN_TYPE_MASK)) goto nla_put_failure; - if (uid_valid(tun->owner) && + if (uid_valid(owner) && nla_put_u32(skb, IFLA_TUN_OWNER, - from_kuid_munged(current_user_ns(), tun->owner))) + from_kuid_munged(current_user_ns(), owner))) goto nla_put_failure; - if (gid_valid(tun->group) && + if (gid_valid(group) && nla_put_u32(skb, IFLA_TUN_GROUP, - from_kgid_munged(current_user_ns(), tun->group))) + from_kgid_munged(current_user_ns(), group))) goto nla_put_failure; - if (nla_put_u8(skb, IFLA_TUN_PI, !(tun->flags & IFF_NO_PI))) + if (nla_put_u8(skb, IFLA_TUN_PI, !(flags & IFF_NO_PI))) goto nla_put_failure; - if (nla_put_u8(skb, IFLA_TUN_VNET_HDR, !!(tun->flags & IFF_VNET_HDR))) + if (nla_put_u8(skb, IFLA_TUN_VNET_HDR, !!(flags & IFF_VNET_HDR))) goto nla_put_failure; - if (nla_put_u8(skb, IFLA_TUN_PERSIST, !!(tun->flags & IFF_PERSIST))) + if (nla_put_u8(skb, IFLA_TUN_PERSIST, !!(flags & IFF_PERSIST))) goto nla_put_failure; if (nla_put_u8(skb, IFLA_TUN_MULTI_QUEUE, - !!(tun->flags & IFF_MULTI_QUEUE))) + !!(flags & IFF_MULTI_QUEUE))) goto nla_put_failure; - if (tun->flags & IFF_MULTI_QUEUE) { - if (nla_put_u32(skb, IFLA_TUN_NUM_QUEUES, tun->numqueues)) + if (flags & IFF_MULTI_QUEUE) { + if (nla_put_u32(skb, IFLA_TUN_NUM_QUEUES, + READ_ONCE(tun->numqueues))) goto nla_put_failure; if (nla_put_u32(skb, IFLA_TUN_NUM_DISABLED_QUEUES, - tun->numdisabled)) + READ_ONCE(tun->numdisabled))) goto nla_put_failure; } @@ -2814,8 +2818,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) return 0; } - tun->flags = (tun->flags & ~TUN_FEATURES) | - (ifr->ifr_flags & TUN_FEATURES); + WRITE_ONCE(tun->flags, (tun->flags & ~TUN_FEATURES) | + (ifr->ifr_flags & TUN_FEATURES)); netdev_state_change(dev); } else { @@ -3213,13 +3217,13 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, /* Disable/Enable persist mode. Keep an extra reference to the * module to prevent the module being unprobed. */ - if (arg && !(tun->flags & IFF_PERSIST)) { - tun->flags |= IFF_PERSIST; + if (arg && !(READ_ONCE(tun->flags) & IFF_PERSIST)) { + WRITE_ONCE(tun->flags, READ_ONCE(tun->flags) | IFF_PERSIST); __module_get(THIS_MODULE); do_notify = true; } - if (!arg && (tun->flags & IFF_PERSIST)) { - tun->flags &= ~IFF_PERSIST; + if (!arg && (READ_ONCE(tun->flags) & IFF_PERSIST)) { + WRITE_ONCE(tun->flags, READ_ONCE(tun->flags) & ~IFF_PERSIST); module_put(THIS_MODULE); do_notify = true; } @@ -3235,10 +3239,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, ret = -EINVAL; break; } - tun->owner = owner; + WRITE_ONCE(tun->owner, owner); do_notify = true; netif_info(tun, drv, tun->dev, "owner set to %u\n", - from_kuid(&init_user_ns, tun->owner)); + from_kuid(&init_user_ns, owner)); break; case TUNSETGROUP: @@ -3248,10 +3252,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, ret = -EINVAL; break; } - tun->group = group; + WRITE_ONCE(tun->group, group); do_notify = true; netif_info(tun, drv, tun->dev, "group set to %u\n", - from_kgid(&init_user_ns, tun->group)); + from_kgid(&init_user_ns, group)); break; case TUNSETLINK: diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h index fa5cab9d3e55..f4c652b1fa44 100644 --- a/drivers/net/tun_vnet.h +++ b/drivers/net/tun_vnet.h @@ -40,9 +40,9 @@ static inline long tun_set_vnet_be(unsigned int *flags, int __user *argp) return -EFAULT; if (be) - *flags |= TUN_VNET_BE; + WRITE_ONCE(*flags, *flags | TUN_VNET_BE); else - *flags &= ~TUN_VNET_BE; + WRITE_ONCE(*flags, *flags & ~TUN_VNET_BE); return 0; } @@ -93,9 +93,9 @@ static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags, if (get_user(s, sp)) return -EFAULT; if (s) - *flags |= TUN_VNET_LE; + WRITE_ONCE(*flags, *flags | TUN_VNET_LE); else - *flags &= ~TUN_VNET_LE; + WRITE_ONCE(*flags, *flags & ~TUN_VNET_LE); return 0; case TUNGETVNETBE: