[PATCH 3.16 072/136] net: avoid potential infinite loop in tc_ctl_action()

Ben Hutchings
2019-12-17T00:52:20Z

From: Eric Dumazet <edumazet@google.com>

commit 39f13ea2f61b439ebe0060393e9c39925c9ee28c upstream.

tc_ctl_action() has the ability to loop forever if tcf_action_add()
returns -EAGAIN.

This special case has been done in case a module needed to be loaded,
but it turns out that tcf_add_notify() could also return -EAGAIN
if the socket sk_rcvbuf limit is hit.

We need to separate the two cases, and only loop for the module
loading case.

While we are at it, add a limit of 10 attempts since unbounded
loops are always scary.

syzbot repro was something like :

socket(PF_NETLINK, SOCK_RAW|SOCK_NONBLOCK, NETLINK_ROUTE) = 3
write(3, ..., 38) = 38
setsockopt(3, SOL_SOCKET, SO_RCVBUF, [0], 4) = 0
sendmsg(3, {msg_name(0)=NULL, msg_iov(1)=[{..., 388}], msg_controllen=0, msg_flags=0x10}, ...)

NMI backtrace for cpu 0
CPU: 0 PID: 1054 Comm: khungtaskd Not tainted 5.4.0-rc1+ #0
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+0x172/0x1f0 lib/dump_stack.c:113
nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x23b/0x28b lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0x9d0/0xef0 kernel/hung_task.c:289
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 8859 Comm: syz-executor910 Not tainted 5.4.0-rc1+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:arch_local_save_flags arch/x86/include/asm/paravirt.h:751 [inline]
RIP: 0010:lockdep_hardirqs_off+0x1df/0x2e0 kernel/locking/lockdep.c:3453
Code: 5c 08 00 00 5b 41 5c 41 5d 5d c3 48 c7 c0 58 1d f3 88 48 ba 00 00 00 00 00 fc ff df 48 c1 e8 03 80 3c 10 00 0f 85 d3 00 00 00 <48> 83 3d 21 9e 99 07 00 0f 84 b9 00 00 00 9c 58 0f 1f 44 00 00 f6
RSP: 0018:ffff8880a6f3f1b8 EFLAGS: 00000046
RAX: 1ffffffff11e63ab RBX: ffff88808c9c6080 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000000 RDI: ffff88808c9c6914
RBP: ffff8880a6f3f1d0 R08: ffff88808c9c6080 R09: fffffbfff16be5d1
R10: fffffbfff16be5d0 R11: 0000000000000003 R12: ffffffff8746591f
R13: ffff88808c9c6080 R14: ffffffff8746591f R15: 0000000000000003
FS: 00000000011e4880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 00000000a8920000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
trace_hardirqs_off+0x62/0x240 kernel/trace/trace_preemptirq.c:45
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
_raw_spin_lock_irqsave+0x6f/0xcd kernel/locking/spinlock.c:159
__wake_up_common_lock+0xc8/0x150 kernel/sched/wait.c:122
__wake_up+0xe/0x10 kernel/sched/wait.c:142
netlink_unlock_table net/netlink/af_netlink.c:466 [inline]
netlink_unlock_table net/netlink/af_netlink.c:463 [inline]
netlink_broadcast_filtered+0x705/0xb80 net/netlink/af_netlink.c:1514
netlink_broadcast+0x3a/0x50 net/netlink/af_netlink.c:1534
rtnetlink_send+0xdd/0x110 net/core/rtnetlink.c:714
tcf_add_notify net/sched/act_api.c:1343 [inline]
tcf_action_add+0x243/0x370 net/sched/act_api.c:1362
tc_ctl_action+0x3b5/0x4bc net/sched/act_api.c:1410
rtnetlink_rcv_msg+0x463/0xb00 net/core/rtnetlink.c:5386
netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5404
netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
netlink_unicast+0x531/0x710 net/netlink/af_netlink.c:1328
netlink_sendmsg+0x8a5/0xd60 net/netlink/af_netlink.c:1917
sock_sendmsg_nosec net/socket.c:637 [inline]
sock_sendmsg+0xd7/0x130 net/socket.c:657
___sys_sendmsg+0x803/0x920 net/socket.c:2311
__sys_sendmsg+0x105/0x1d0 net/socket.c:2356
__do_sys_sendmsg net/socket.c:2365 [inline]
__se_sys_sendmsg net/socket.c:2363 [inline]
__x64_sys_sendmsg+0x78/0xb0 net/socket.c:2363
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440939

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot+cf0adbb9c28c8866c788@syzkaller.appspotmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -923,10 +923,15 @@ static int
tcf_action_add(struct net *net, struct nlattr *nla, struct nlmsghdr *n,
u32 portid, int ovr)
{
- int ret = 0;
+ int loop, ret;
LIST_HEAD(actions);

- ret = tcf_action_init(net, nla, NULL, NULL, ovr, 0, &actions);
+ for (loop = 0; loop < 10; loop++) {
+ ret = tcf_action_init(net, nla, NULL, NULL, ovr, 0, &actions);
+ if (ret != -EAGAIN)
+ break;
+ }
+
if (ret)
goto done;

@@ -969,10 +974,7 @@ static int tc_ctl_action(struct sk_buff
*/
if (n->nlmsg_flags & NLM_F_REPLACE)
ovr = 1;
-replay:
ret = tcf_action_add(net, tca[TCA_ACT_TAB], n, portid, ovr);
- if (ret == -EAGAIN)
- goto replay;
break;
case RTM_DELACTION:
ret = tca_action_gd(net, tca[TCA_ACT_TAB], n,