[PATCH 5.4 1/1] tun: avoid double free in tun_free_netdev

[Dragos-Marian Panait]

From: George Kennedy <george.kennedy@xxxxxxxxxx>

commit 158b515f703e75e7d68289bf4d98c664e1d632df upstream.

Avoid double free in tun_free_netdev() by moving the
dev->tstats and tun->security allocs to a new ndo_init routine
(tun_net_init()) that will be called by register_netdevice().
ndo_init is paired with the desctructor (tun_free_netdev()),
so if there's an error in register_netdevice() the destructor
will handle the frees.

BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605

CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
____kasan_slab_free mm/kasan/common.c:346 [inline]
__kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook mm/slub.c:1749 [inline]
slab_free mm/slub.c:3513 [inline]
kfree+0xac/0x2d0 mm/slub.c:4561
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
__tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Link: https://lore.kernel.org/r/1639679132-19884-1-git-send-email-george.kennedy@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
[DP: adjusted context for 5.4 stable]
Signed-off-by: Dragos-Marian Panait <dragos.panait@xxxxxxxxxxxxx>
---
 drivers/net/tun.c | 109 +++++++++++++++++++++++++---------------------
 1 file changed, 59 insertions(+), 50 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 5d94ac0250ec..a4e44f98fbc3 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -250,6 +250,9 @@ struct tun_struct {
 	struct tun_prog __rcu *steering_prog;
 	struct tun_prog __rcu *filter_prog;
 	struct ethtool_link_ksettings link_ksettings;
+	/* init args */
+	struct file *file;
+	struct ifreq *ifr;
 };
 
 struct veth {
@@ -275,6 +278,9 @@ void *tun_ptr_to_xdp(void *ptr)
 }
 EXPORT_SYMBOL(tun_ptr_to_xdp);
 
+static void tun_flow_init(struct tun_struct *tun);
+static void tun_flow_uninit(struct tun_struct *tun);
+
 static int tun_napi_receive(struct napi_struct *napi, int budget)
 {
 	struct tun_file *tfile = container_of(napi, struct tun_file, napi);
@@ -1027,6 +1033,49 @@ static int check_filter(struct tap_filter *filter, const struct sk_buff *skb)
 
 static const struct ethtool_ops tun_ethtool_ops;
 
+static int tun_net_init(struct net_device *dev)
+{
+	struct tun_struct *tun = netdev_priv(dev);
+	struct ifreq *ifr = tun->ifr;
+	int err;
+
+	tun->pcpu_stats = netdev_alloc_pcpu_stats(struct tun_pcpu_stats);
+	if (!tun->pcpu_stats)
+		return -ENOMEM;
+
+	spin_lock_init(&tun->lock);
+
+	err = security_tun_dev_alloc_security(&tun->security);
+	if (err < 0) {
+		free_percpu(tun->pcpu_stats);
+		return err;
+	}
+
+	tun_flow_init(tun);
+
+	dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
+			   TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
+			   NETIF_F_HW_VLAN_STAG_TX;
+	dev->features = dev->hw_features | NETIF_F_LLTX;
+	dev->vlan_features = dev->features &
+			     ~(NETIF_F_HW_VLAN_CTAG_TX |
+			       NETIF_F_HW_VLAN_STAG_TX);
+
+	tun->flags = (tun->flags & ~TUN_FEATURES) |
+		      (ifr->ifr_flags & TUN_FEATURES);
+
+	INIT_LIST_HEAD(&tun->disabled);
+	err = tun_attach(tun, tun->file, false, ifr->ifr_flags & IFF_NAPI,
+			 ifr->ifr_flags & IFF_NAPI_FRAGS, false);
+	if (err < 0) {
+		tun_flow_uninit(tun);
+		security_tun_dev_free_security(tun->security);
+		free_percpu(tun->pcpu_stats);
+		return err;
+	}
+	return 0;
+}
+
 /* Net device detach from fd. */
 static void tun_net_uninit(struct net_device *dev)
 {
@@ -1285,6 +1334,7 @@ static int tun_net_change_carrier(struct net_device *dev, bool new_carrier)
 }
 
 static const struct net_device_ops tun_netdev_ops = {
+	.ndo_init		= tun_net_init,
 	.ndo_uninit		= tun_net_uninit,
 	.ndo_open		= tun_net_open,
 	.ndo_stop		= tun_net_close,
@@ -1365,6 +1415,7 @@ static int tun_xdp_tx(struct net_device *dev, struct xdp_buff *xdp)
 }
 
 static const struct net_device_ops tap_netdev_ops = {
+	.ndo_init		= tun_net_init,
 	.ndo_uninit		= tun_net_uninit,
 	.ndo_open		= tun_net_open,
 	.ndo_stop		= tun_net_close,
@@ -1405,7 +1456,7 @@ static void tun_flow_uninit(struct tun_struct *tun)
 #define MAX_MTU 65535
 
 /* Initialize net device. */
-static void tun_net_init(struct net_device *dev)
+static void tun_net_initialize(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
 
@@ -2839,9 +2890,6 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 		if (!dev)
 			return -ENOMEM;
-		err = dev_get_valid_name(net, dev, name);
-		if (err < 0)
-			goto err_free_dev;
 
 		dev_net_set(dev, net);
 		dev->rtnl_link_ops = &tun_link_ops;
@@ -2860,41 +2908,16 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 		tun->rx_batched = 0;
 		RCU_INIT_POINTER(tun->steering_prog, NULL);
 
-		tun->pcpu_stats = netdev_alloc_pcpu_stats(struct tun_pcpu_stats);
-		if (!tun->pcpu_stats) {
-			err = -ENOMEM;
-			goto err_free_dev;
-		}
-
-		spin_lock_init(&tun->lock);
-
-		err = security_tun_dev_alloc_security(&tun->security);
-		if (err < 0)
-			goto err_free_stat;
-
-		tun_net_init(dev);
-		tun_flow_init(tun);
-
-		dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
-				   TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
-				   NETIF_F_HW_VLAN_STAG_TX;
-		dev->features = dev->hw_features | NETIF_F_LLTX;
-		dev->vlan_features = dev->features &
-				     ~(NETIF_F_HW_VLAN_CTAG_TX |
-				       NETIF_F_HW_VLAN_STAG_TX);
+		tun->ifr = ifr;
+		tun->file = file;
 
-		tun->flags = (tun->flags & ~TUN_FEATURES) |
-			      (ifr->ifr_flags & TUN_FEATURES);
-
-		INIT_LIST_HEAD(&tun->disabled);
-		err = tun_attach(tun, file, false, ifr->ifr_flags & IFF_NAPI,
-				 ifr->ifr_flags & IFF_NAPI_FRAGS, false);
-		if (err < 0)
-			goto err_free_flow;
+		tun_net_initialize(dev);
 
 		err = register_netdevice(tun->dev);
-		if (err < 0)
-			goto err_detach;
+		if (err < 0) {
+			free_netdev(dev);
+			return err;
+		}
 		/* free_netdev() won't check refcnt, to aovid race
 		 * with dev_put() we need publish tun after registration.
 		 */
@@ -2913,20 +2936,6 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 	strcpy(ifr->ifr_name, tun->dev->name);
 	return 0;
-
-err_detach:
-	tun_detach_all(dev);
-	/* register_netdevice() already called tun_free_netdev() */
-	goto err_free_dev;
-
-err_free_flow:
-	tun_flow_uninit(tun);
-	security_tun_dev_free_security(tun->security);
-err_free_stat:
-	free_percpu(tun->pcpu_stats);
-err_free_dev:
-	free_netdev(dev);
-	return err;
 }
 
 static void tun_get_iff(struct tun_struct *tun, struct ifreq *ifr)
-- 
2.39.1