Re: [PATCH] xdp: remove WARN() from __xdp_reg_mem_model()

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 17/06/2024 18.27, Daniil Dulov wrote:
> Syzkaller reports a warning in __xdp_reg_mem_model().
> 
> The warning occurs only if __mem_id_init_hash_table() returns
> an error. It returns the error in two cases:
> 
>      1. memory allocation fails;
>      2. rhashtable_init() fails when some fields of rhashtable_params
>         struct are not initialized properly.
> 
> The second case cannot happen since there is a static const
> rhashtable_params struct with valid fields. So, warning is only triggered
> when there is a problem with memory allocation.
> 
> Thus, there is no sense in using WARN() to handle this error and it can be
> safely removed.
> 
> WARNING: CPU: 0 PID: 5065 at net/core/xdp.c:299 __xdp_reg_mem_model+0x2d9/0x650 net/core/xdp.c:299
> 
> CPU: 0 PID: 5065 Comm: syz-executor883 Not tainted 6.8.0-syzkaller-05271-gf99c5f563c17 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> RIP: 0010:__xdp_reg_mem_model+0x2d9/0x650 net/core/xdp.c:299
> 
> Call Trace:
>   xdp_reg_mem_model+0x22/0x40 net/core/xdp.c:344
>   xdp_test_run_setup net/bpf/test_run.c:188 [inline]
>   bpf_test_run_xdp_live+0x365/0x1e90 net/bpf/test_run.c:377
>   bpf_prog_test_run_xdp+0x813/0x11b0 net/bpf/test_run.c:1267
>   bpf_prog_test_run+0x33a/0x3b0 kernel/bpf/syscall.c:4240
>   __sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5649
>   __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
>   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736
>   do_syscall_64+0xfb/0x240
>   entry_SYSCALL_64_after_hwframe+0x6d/0x75
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Fixes: 8d5d88527587 ("xdp: rhashtable with allocator ID to pointer mapping")
> Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
> ---
>   net/core/xdp.c | 1 -
>   1 file changed, 1 deletion(-)
> 

Sure, looks like we can remove this WARN_ON()

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>

> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 41693154e426..fb2f00e3f701 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -296,7 +296,6 @@ static struct xdp_mem_allocator *__xdp_reg_mem_model(struct xdp_mem_info *mem,
>   		ret = __mem_id_init_hash_table();
>   		mutex_unlock(&mem_id_lock);
>   		if (ret < 0) {
> -			WARN_ON(1);
>   			return ERR_PTR(ret);
>   		}
>   	}