Re: [PATCH net v2] 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 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().
> 
> Fixes: 05f00505a89a ("ipvs: fix crash if scheduler is changed")
> Reported-by: Xiang Mei <xmei5@xxxxxxx>
> Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>

        Looks good to me, thanks!

Acked-by: Julian Anastasov <ja@xxxxxx>

        But the problem popups in more recent kernels (6.2, not 4.2),
when the new error path is added after the ip_vs_start_estimator()
call in commit 705dd3444081 ("ipvs: use kthreads for stats estimation").

> ---
> v2: Remove "sched = NULL" instead of recovering it in out_err (Julian)
> 
>  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 35642de2a0fee..2aaf50f52c8e8 100644
> --- a/net/netfilter/ipvs/ip_vs_ctl.c
> +++ b/net/netfilter/ipvs/ip_vs_ctl.c
> @@ -1452,7 +1452,6 @@ 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);
> -- 
> 2.43.0

Regards

--
Julian Anastasov <ja@xxxxxx>