ipvs: fix NULL deref in ip_vs_add_service error path

In the Linux kernel, the following vulnerability has been resolved:

ipvs: fix NULL deref in ip_vs_add_service error path

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.