If a netlink socket sends RTM_GETCHAIN requests repeatedly
without recv()ing the responses, tc_ctl_chain() hogs CPU and
triggers Hung Task splat. [0]
As caught in the stack trace, netlink_attachskb() could confuse
tc_ctl_chain() by returning -EAGAIN when the userspace netlink
socket's receive buffer is full.
The replay: label exists since commit 32a4f5ecd738 ("net: sched:
introduce chain object to uapi") but was not used initially.
Since commit 9f407f1768d3 ("net: sched: introduce chain templates"),
the label is needed for RTM_NEWCHAIN because tcf_proto_lookup_ops()
may release RTNL to call request_module().
However, the replay logic is unnecessary for RTM_GETCHAIN.
Let's apply the replay logic only for RTM_NEWCHAIN.
[0]:
INFO: task repro:1018 is blocked on a mutex likely owned by task repro:1022.
task:repro state:R running task stack:14096 pid:1022 tgid:1014 ppid:961 task_flags:0x400040 flags:0x00080000
Call Trace:
? clockevents_program_event (kernel/time/clockevents.c:372)
? pskb_expand_head (net/core/skbuff.c:615)
? skb_release_data (net/core/skbuff.c:1122)
? netlink_attachskb (./include/linux/skbuff.h:1323 ./include/linux/skbuff.h:1332 net/netlink/af_netlink.c:1232)
? __netlink_lookup (./include/linux/rcupdate.h:882 ./include/linux/rhashtable.h:711 net/netlink/af_netlink.c:499)
? tc_chain_notify (net/sched/cls_api.c:3045)
? tc_chain_notify (./include/linux/skbuff.h:1384 net/sched/cls_api.c:3041)
? netlink_unicast (net/netlink/af_netlink.c:1335)
? rtnl_unicast (./include/net/netlink.h:1198 net/core/rtnetlink.c:985)
? tc_ctl_chain (net/sched/cls_api.c:3242)
? rtnetlink_rcv_msg (net/core/rtnetlink.c:7146)
? netlink_unicast (net/netlink/af_netlink.c:1354)
? __pfx_rtnetlink_rcv_msg (net/core/rtnetlink.c:7177)
? netlink_rcv_skb (net/netlink/af_netlink.c:2556)
? netlink_unicast (net/netlink/af_netlink.c:1319)
? netlink_sendmsg (net/netlink/af_netlink.c:1900)
? __sock_sendmsg (net/socket.c:800)
? __sys_sendto (net/socket.c:2281)
? __x64_sys_sendto (net/socket.c:2288 net/socket.c:2284 net/socket.c:2284)
? do_syscall_64 (arch/x86/entry/syscall_64.c:61 arch/x86/entry/syscall_64.c:84)
? entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
Fixes: 2ed9db3074fc ("net: sched: cls_api: fix dead code in switch")
Reported-by: Taras Madan
Signed-off-by: Kuniyuki Iwashima
---
net/sched/cls_api.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 9966766661d5..c47d2ee13641 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -3254,7 +3254,7 @@ static int tc_ctl_chain(struct sk_buff *skb, struct nlmsghdr *n,
tcf_chain_put(chain);
errout_block:
tcf_block_release(q, block, true);
- if (err == -EAGAIN)
+ if (err == -EAGAIN && n->nlmsg_type == RTM_NEWCHAIN)
/* Replay the request. */
goto replay;
return err;
--
2.55.0.979.g7e5102b832-goog