[PATCH net] ipvs: fix NULL deref in ip_vs_add_service error path

[Weiming Shi <bestswngs@xxxxxxxxx>]

When ip_vs_bind_scheduler() succeeds in ip_vs_add_service(), the local
variable sched is set to NULL.  If ip_vs_start_estimator() subsequently
fails, the out_err cleanup calls ip_vs_unbind_scheduler(svc, sched)
with sched == NULL.  ip_vs_unbind_scheduler() passes the cur_sched NULL
check (because svc->scheduler was set by the successful bind) but then
dereferences the NULL sched parameter at sched->done_service, causing a
kernel panic at offset 0x30 from NULL.

 Oops: general protection fault, probably for non-canonical address 
0xdffffc0000000006: 0000 [#1] PREEMPT SMP KASAN NOPTI
 KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
 RIP: 0010:ip_vs_unbind_scheduler (net/netfilter/ipvs/ip_vs_sched.c:69)
 Call Trace:
  <TASK>
  ip_vs_add_service.isra.0 (net/netfilter/ipvs/ip_vs_ctl.c:1500)
  do_ip_vs_set_ctl (net/netfilter/ipvs/ip_vs_ctl.c:2809)
  nf_setsockopt (net/netfilter/nf_sockopt.c:102)
  ip_setsockopt (net/ipv4/ip_sockglue.c:1427)
  raw_setsockopt (net/ipv4/raw.c:850)
  do_sock_setsockopt (net/socket.c:2322)
  __sys_setsockopt (net/socket.c:2339)
  __x64_sys_setsockopt (net/socket.c:2350)
  do_syscall_64 (arch/x86/entry/syscall_64.c:94)
  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
  </TASK>

Fix by recovering the scheduler pointer from svc->scheduler before
cleanup when the local sched variable has been cleared.  This also
prevents a latent module refcount leak: without the recovery,
ip_vs_scheduler_put(sched) receives NULL and skips the module_put(),
so the scheduler module could never be unloaded if the kernel survived
past the dereference.

Fixes: 05f00505a89a ("ipvs: fix crash if scheduler is changed")
Reported-by: Xiang Mei <xmei5@xxxxxxx>
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
---
 net/netfilter/ipvs/ip_vs_ctl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 35642de2a0fee..e0c978def9749 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -1497,6 +1497,8 @@ ip_vs_add_service(struct netns_ipvs *ipvs, struct 
ip_vs_service_user_kern *u,
        if (ret_hooks >= 0)
                ip_vs_unregister_hooks(ipvs, u->af);
        if (svc != NULL) {
+               if (!sched)
+                       sched = rcu_dereference_protected(svc->scheduler, 1);
                ip_vs_unbind_scheduler(svc, sched);
                ip_vs_service_free(svc);
        }
-- 
2.43.0