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

[Julian Anastasov <ja@xxxxxx>]

        Hello,

On Wed, 1 Apr 2026, Weiming Shi wrote:

> 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);

        Good catch. But may be it should be enough if
we just remove the sched = NULL after successful
ip_vs_bind_scheduler(), what do you think? ip_vs_unbind_scheduler()
already detects if the scheduler is installed.

>               ip_vs_unbind_scheduler(svc, sched);
>               ip_vs_service_free(svc);

Regards

--
Julian Anastasov <ja@xxxxxx>