linux-kernel - [PATCH] bpf: cgroup: remove WARN_ON at bpf_cgroup_link

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Date:   Sun, 27 Feb 2022 21:40:08 +0800
From:   Dongliang Mu <dzm91@...t.edu.cn>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>
Cc:     Dongliang Mu <mudongliangabcd@...il.com>,
        syzkaller <syzkaller@...glegroups.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] bpf: cgroup: remove WARN_ON at bpf_cgroup_link_release

From: Dongliang Mu <mudongliangabcd@...il.com>

When syzkaller injects fault into memory allocation at
bpf_prog_array_alloc, the kernel encounters a memory failure and
returns non-zero, thus leading to one WARN_ON at
bpf_cgroup_link_release. The stack trace is as follows:

 __kmalloc+0x7e/0x3d0
 bpf_prog_array_alloc+0x4f/0x60
 compute_effective_progs+0x132/0x580
 ? __sanitizer_cov_trace_pc+0x1a/0x40
 update_effective_progs+0x5e/0x260
 __cgroup_bpf_detach+0x293/0x760
 bpf_cgroup_link_release+0xad/0x400
 bpf_link_free+0xca/0x190
 bpf_link_put+0x161/0x1b0
 bpf_link_release+0x33/0x40
 __fput+0x286/0x9f0

Fix this by removing the WARN_ON for __cgroup_bpf_detach.

Reported-by: syzkaller <syzkaller@...glegroups.com>
Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
---
 kernel/bpf/cgroup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 514b4681a90a..fdbdcee6c9fa 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -896,8 +896,8 @@ static void bpf_cgroup_link_release(struct bpf_link *link)
 		return;
 	}

-	WARN_ON(__cgroup_bpf_detach(cg_link->cgroup, NULL, cg_link,
-				    cg_link->type));
+	__cgroup_bpf_detach(cg_link->cgroup, NULL, cg_link,
+				    cg_link->type);

 	cg = cg_link->cgroup;
 	cg_link->cgroup = NULL;
-- 
2.25.1