linux-kernel - [PATCH] xdp: remove WARN() from __xdp_reg_mem

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Message-ID: <20240617162708.492159-1-d.dulov@aladdin.ru>
Date: Mon, 17 Jun 2024 19:27:08 +0300
From: Daniil Dulov <d.dulov@...ddin.ru>
To: Alexei Starovoitov <ast@...nel.org>
CC: Daniil Dulov <d.dulov@...ddin.ru>, Daniel Borkmann <daniel@...earbox.net>,
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend
	<john.fastabend@...il.com>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
	<pabeni@...hat.com>, <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: [PATCH] xdp: remove WARN() from __xdp_reg_mem_model()

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@...ddin.ru>
---
 net/core/xdp.c | 1 -
 1 file changed, 1 deletion(-)

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);
 		}
 	}
-- 
2.25.1