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Date: Mon, 13 Dec 2021 12:04:11 -0500
From: George Kennedy <george.kennedy@...cle.com>
To: kuba@...nel.org
Cc: george.kennedy@...cle.com, stephen@...workplumber.org,
davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2] tun: avoid double free in tun_free_netdev
Avoid double free in tun_free_netdev() by checking if
dev->reg_state is NETREG_UNREGISTERING in the tun_set_iff()
error paths. If dev->reg_state is NETREG_UNREGISTERING that means
the destructor will be called later.
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@...glegroups.com>
Signed-off-by: George Kennedy <george.kennedy@...cle.com>
---
Jakub, decided to go the less code churn route and just
check for dev->reg_state is NETREG_UNREGISTERING.
drivers/net/tun.c | 21 +++++++--------------
1 file changed, 7 insertions(+), 14 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..9ab530a 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2206,10 +2206,6 @@ 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);
@@ -2770,18 +2766,15 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
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);
+ /* if NETREG_UNREGISTERING, destructor will be called later */
+ if (dev->reg_state != NETREG_UNREGISTERING) {
+ tun_flow_uninit(tun);
+ security_tun_dev_free_security(tun->security);
+ }
err_free_stat:
- free_percpu(dev->tstats);
+ if (dev->reg_state != NETREG_UNREGISTERING)
+ free_percpu(dev->tstats);
err_free_dev:
free_netdev(dev);
return err;
--
1.8.3.1
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