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Subject[PATCH v3] tun: avoid double free in tun_free_netdev
Date
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@googlegroups.com>
Signed-off-by: George Kennedy <george.kennedy@oracle.com>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
---
v3: added a new tun_net_init() routine called via ndo_init, which is
called from register_netdevice(). tun_net_init() does the dev->tstats
and tun->security allocs, which if there's an error in
register_netdevice() will be freed by the destructor (tun_free_netdev()).
---
drivers/net/tun.c | 115 ++++++++++++++++++++++++++++--------------------------
1 file changed, 59 insertions(+), 56 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..45a67e7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -209,6 +209,9 @@ 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 {
@@ -216,6 +219,9 @@ struct veth {
__be16 h_vlan_TCI;
};

+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);
@@ -953,6 +959,49 @@ 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;
+
+ dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
+ if (!dev->tstats)
+ return -ENOMEM;
+
+ spin_lock_init(&tun->lock);
+
+ err = security_tun_dev_alloc_security(&tun->security);
+ if (err < 0) {
+ free_percpu(dev->tstats);
+ 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(dev->tstats);
+ return err;
+ }
+ return 0;
+}
+
/* Net device detach from fd. */
static void tun_net_uninit(struct net_device *dev)
{
@@ -1169,6 +1218,7 @@ 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,
@@ -1252,6 +1302,7 @@ 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,
@@ -1292,7 +1343,7 @@ 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);

@@ -2206,11 +2257,6 @@ static void tun_free_netdev(struct net_device *dev)
BUG_ON(!(list_empty(&tun->disabled)));

free_percpu(dev->tstats);
- /* We clear tstats so that tun_set_iff() can tell if
- * tun_free_netdev() has been called from register_netdevice().
- */
- dev->tstats = NULL;
-
tun_flow_uninit(tun);
security_tun_dev_free_security(tun->security);
__tun_set_ebpf(tun, &tun->steering_prog, NULL);
@@ -2716,41 +2762,16 @@ 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);

- dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
- if (!dev->tstats) {
- 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);
+ tun->ifr = ifr;
+ tun->file = file;

- 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, 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 avoid race
* with dev_put() we need publish tun after registration.
*/
@@ -2767,24 +2788,6 @@ 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);
- /* We are here because register_netdevice() has failed.
- * If register_netdevice() already called tun_free_netdev()
- * while dealing with the error, dev->stats has been cleared.
- */
- if (!dev->tstats)
- goto err_free_dev;
-
-err_free_flow:
- tun_flow_uninit(tun);
- security_tun_dev_free_security(tun->security);
-err_free_stat:
- free_percpu(dev->tstats);
-err_free_dev:
- free_netdev(dev);
- return err;
}

static void tun_get_iff(struct tun_struct *tun, struct ifreq *ifr)
--
1.8.3.1
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