WARNING in cttimeout_default_get

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: da5322e65940 Merge tag 'selinux-pr-20181115' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15d719eb400000
kernel config: https://syzkaller.appspot.com/x/.config?x=4a0a89f12ca9b0f5
dashboard link: https://syzkaller.appspot.com/bug?extid=2fae8fa157dd92618cae
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=129e0893400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=125f66a3400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2fae8f...@syzkaller.appspotmail.com

audit: type=1800 audit(1542315810.422:30): pid=5877 uid=0 auid=4294967295
ses=4294967295 subj==unconfined op=collect_data cause=failed(directio)
comm="startpar" name="rmnologin" dev="sda1" ino=2423 res=0
netlink: 'syz-executor298': attribute type 3 has an invalid length.
netlink: 'syz-executor298': attribute type 2 has an invalid length.
WARNING: CPU: 0 PID: 6032 at net/netfilter/nfnetlink_cttimeout.c:478
cttimeout_default_get+0x1df/0xb30 net/netfilter/nfnetlink_cttimeout.c:478
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 6032 Comm: syz-executor298 Not tainted 4.20.0-rc2+ #336
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
panic+0x2ad/0x55c kernel/panic.c:188
__warn.cold.8+0x20/0x45 kernel/panic.c:540
report_bug+0x254/0x2d0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:cttimeout_default_get+0x1df/0xb30
net/netfilter/nfnetlink_cttimeout.c:478
Code: 00 0f 87 8d 00 00 00 41 80 ff 06 0f 84 94 07 00 00 41 80 ff 11 0f 84
6c 07 00 00 41 80 ff 01 0f 84 44 07 00 00 e8 91 f1 20 fb <0f> 0b 41 bd a1
ff ff ff eb 06 41 bd a1 ff ff ff e8 7c f1 20 fb 48
RSP: 0018:ffff8881b64c72b0 EFLAGS: 00010293
RAX: ffff8881c1686380 RBX: ffffffff88bf58e0 RCX: ffffffff865e961c
RDX: 0000000000000000 RSI: ffffffff865e964f RDI: 0000000000000001
RBP: ffff8881b64c73c0 R08: ffff8881c1686380 R09: ffffed103b5c5b67
R10: 0000000000000002 R11: ffff8881dae2db3b R12: 0000000000000088
R13: ffff8881bf42b300 R14: 0000000000000000 R15: 0000000000000088
nfnetlink_rcv_msg+0xdd3/0x10c0 net/netfilter/nfnetlink.c:228
netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2477
nfnetlink_rcv+0x1c0/0x4d0 net/netfilter/nfnetlink.c:560
netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
netlink_unicast+0x5a5/0x760 net/netlink/af_netlink.c:1336
netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1917
sock_sendmsg_nosec net/socket.c:621 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:631
___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
__sys_sendmsg+0x11d/0x280 net/socket.c:2154
__do_sys_sendmsg net/socket.c:2163 [inline]
__se_sys_sendmsg net/socket.c:2161 [inline]
__x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4400d9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc704c30c8 EFLAGS: 00000213 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004400d9
RDX: 0000000000000000 RSI: 0000000020dddfc8 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000213 R12: 0000000000401960
R13: 00000000004019f0 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Florian Westphal]

syzbot was able to trigger the WARN in cttimeout_default_get() by
passing UDPLITE as l4protocol. Alias UDPLITE to UDP, both use
same timeout values.

Furthermore, also fetch GRE timeouts. GRE is a bit more complicated,
as it still can be a module and its netns_proto_gre struct layout isn't
visible outside of the gre module.

Work around this by forcing the timeouts to be the first structure
member, then use plain net_generic().

A followup nf-next patch could make gre tracker be built-in as well
if needed, its not that large.

Last, make the WARN() mention the missing protocol value in case
anything else is missing.

Reported-by: syzbot+2fae8f...@syzkaller.appspotmail.com
Fixes: 8866df9264a3 ("netfilter: nfnetlink_cttimeout: pass default timeout policy to obj_to_nlattr")
Signed-off-by: Florian Westphal <f...@strlen.de>
---
net/netfilter/nf_conntrack_proto_gre.c | 4 +++-
net/netfilter/nfnetlink_cttimeout.c | 11 +++++++++--
2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nf_conntrack_proto_gre.c b/net/netfilter/nf_conntrack_proto_gre.c
index 9b48dc8b4b88..dd8db7fbc437 100644
--- a/net/netfilter/nf_conntrack_proto_gre.c
+++ b/net/netfilter/nf_conntrack_proto_gre.c
@@ -56,10 +56,10 @@ static const unsigned int gre_timeouts[GRE_CT_MAX] = {

static unsigned int proto_gre_net_id __read_mostly;
struct netns_proto_gre {
+ unsigned int gre_timeouts[GRE_CT_MAX];
struct nf_proto_net nf;
rwlock_t keymap_lock;
struct list_head keymap_list;
- unsigned int gre_timeouts[GRE_CT_MAX];
};

static inline struct netns_proto_gre *gre_pernet(struct net *net)
@@ -402,6 +402,8 @@ static int __init nf_ct_proto_gre_init(void)
{
int ret;

+ BUILD_BUG_ON(offsetof(struct netns_proto_gre, gre_timeouts));
+
ret = register_pernet_subsys(&proto_gre_net_ops);
if (ret < 0)
goto out_pernet;
diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
index a518eb162344..1643faa35f56 100644
--- a/net/netfilter/nfnetlink_cttimeout.c
+++ b/net/netfilter/nfnetlink_cttimeout.c
@@ -455,7 +455,8 @@ static int cttimeout_default_get(struct net *net, struct sock *ctnl,
case IPPROTO_TCP:
timeouts = nf_tcp_pernet(net)->timeouts;
break;
- case IPPROTO_UDP:
+ case IPPROTO_UDP: /* fallthrough */
+ case IPPROTO_UDPLITE:
timeouts = nf_udp_pernet(net)->timeouts;
break;
case IPPROTO_DCCP:
@@ -469,13 +470,19 @@ static int cttimeout_default_get(struct net *net, struct sock *ctnl,
case IPPROTO_SCTP:
#ifdef CONFIG_NF_CT_PROTO_SCTP
timeouts = nf_sctp_pernet(net)->timeouts;
+#endif
+ break;
+ case IPPROTO_GRE:
+#ifdef CONFIG_NF_CT_PROTO_GRE
+ if (l4proto->net_id)
+ timeouts = net_generic(net, *l4proto->net_id);
#endif
break;
case 255:
timeouts = &nf_generic_pernet(net)->timeout;
break;
default:
- WARN_ON_ONCE(1);
+ WARN_ONCE(1, "Missing timeouts for proto %d", l4proto->l4proto);
break;
}

--
2.18.1

[Pablo Neira Ayuso]

On Sat, Nov 17, 2018 at 11:32:29AM +0100, Florian Westphal wrote:
> syzbot was able to trigger the WARN in cttimeout_default_get() by
> passing UDPLITE as l4protocol. Alias UDPLITE to UDP, both use
> same timeout values.
>
> Furthermore, also fetch GRE timeouts. GRE is a bit more complicated,
> as it still can be a module and its netns_proto_gre struct layout isn't
> visible outside of the gre module.
>
> Work around this by forcing the timeouts to be the first structure
> member, then use plain net_generic().
>
> A followup nf-next patch could make gre tracker be built-in as well
> if needed, its not that large.
>
> Last, make the WARN() mention the missing protocol value in case
> anything else is missing.

Applied, thanks Florian.