[PATCH AUTOSEL 6.18] ipvs: fix NULL deref in ip_vs_add_service error path

[Sasha Levin <sashal@xxxxxxxxxx>]

From: Weiming Shi <bestswngs@xxxxxxxxx>

[ Upstream commit 9a91797e61d286805ae10a92cc48959c30800556 ]

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, [..] [#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)
  [..]

Fix by simply not clearing the local sched variable after a successful
bind.  ip_vs_unbind_scheduler() already detects whether a scheduler is
installed via svc->scheduler, and keeping sched non-NULL ensures the
error path passes the correct pointer to both ip_vs_unbind_scheduler()
and ip_vs_scheduler_put().

While the bug is older, the problem popups in more recent kernels (6.2),
when the new error path is taken after the ip_vs_start_estimator() call.

Fixes: 705dd3444081 ("ipvs: use kthreads for stats estimation")
Reported-by: Xiang Mei <xmei5@xxxxxxx>
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
Acked-by: Simon Horman <horms@xxxxxxxxxx>
Acked-by: Julian Anastasov <ja@xxxxxx>
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 net/netfilter/ipvs/ip_vs_ctl.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 4c8fa22be88ad..e442ba6033d5f 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -1453,7 +1453,6 @@ ip_vs_add_service(struct netns_ipvs *ipvs, struct 
ip_vs_service_user_kern *u,
                ret = ip_vs_bind_scheduler(svc, sched);
                if (ret)
                        goto out_err;
-               sched = NULL;
        }
 
        ret = ip_vs_start_estimator(ipvs, &svc->stats);
-- 
2.53.0