[PATCH 3.16 361/370] sit: fix a double free on error path

Ben Hutchings
2017-03-10T12:15:42Z

From: WANG Cong <xiyou.wangcong@gmail.com>

[ Upstream commit d7426c69a1942b2b9b709bf66b944ff09f561484 ]

Dmitry reported a double free in sit_init_net():

kernel BUG at mm/percpu.c:689!
invalid opcode: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 15692 Comm: syz-executor1 Not tainted 4.10.0-rc6-next-20170206 #1
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
task: ffff8801c9cc27c0 task.stack: ffff88017d1d8000
RIP: 0010:pcpu_free_area+0x68b/0x810 mm/percpu.c:689
RSP: 0018:ffff88017d1df488 EFLAGS: 00010046
RAX: 0000000000010000 RBX: 00000000000007c0 RCX: ffffc90002829000
RDX: 0000000000010000 RSI: ffffffff81940efb RDI: ffff8801db841d94
RBP: ffff88017d1df590 R08: dffffc0000000000 R09: 1ffffffff0bb3bdd
R10: dffffc0000000000 R11: 00000000000135dd R12: ffff8801db841d80
R13: 0000000000038e40 R14: 00000000000007c0 R15: 00000000000007c0
FS: 00007f6ea608f700(0000) GS:ffff8801dbe00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000002000aff8 CR3: 00000001c8d44000 CR4: 00000000001426f0
DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
free_percpu+0x212/0x520 mm/percpu.c:1264
ipip6_dev_free+0x43/0x60 net/ipv6/sit.c:1335
sit_init_net+0x3cb/0xa10 net/ipv6/sit.c:1831
ops_init+0x10a/0x530 net/core/net_namespace.c:115
setup_net+0x2ed/0x690 net/core/net_namespace.c:291
copy_net_ns+0x26c/0x530 net/core/net_namespace.c:396
create_new_namespaces+0x409/0x860 kernel/nsproxy.c:106
unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:205
SYSC_unshare kernel/fork.c:2281 [inline]
SyS_unshare+0x64e/0xfc0 kernel/fork.c:2231
entry_SYSCALL_64_fastpath+0x1f/0xc2

This is because when tunnel->dst_cache init fails, we free dev->tstats
once in ipip6_tunnel_init() and twice in sit_init_net(). This looks
redundant but its ndo_uinit() does not seem enough to clean up everything
here. So avoid this by setting dev->tstats to NULL after the first free,
at least for -net.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv6/sit.c | 1 +
1 file changed, 1 insertion(+)

--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -1368,6 +1368,7 @@ static int ipip6_tunnel_init(struct net_
tunnel->dst_cache = alloc_percpu(struct ip_tunnel_dst);
if (!tunnel->dst_cache) {
free_percpu(dev->tstats);
+ dev->tstats = NULL;
return -ENOMEM;
}