Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Peilin Ye <yepeilin.cs@gmail.com>
To:     Andrii Nakryiko <andriin@fb.com>
Cc:     Peilin Ye <yepeilin.cs@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [Linux-kernel-mentees] [PATCH v2] bpf: Fix NULL pointer dereference in __btf_resolve_helper_id()
Date:   Mon, 13 Jul 2020 21:27:32 -0400
Message-Id: <20200714012732.195466-1-yepeilin.cs@gmail.com>
In-Reply-To: <CAEf4BzZRGOsTiW3uFWd1aY6K5Yi+QBrTeC5FNOo6uVXviXuX4g@mail.gmail.com>
References: <CAEf4BzZRGOsTiW3uFWd1aY6K5Yi+QBrTeC5FNOo6uVXviXuX4g@mail.gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Prevent __btf_resolve_helper_id() from dereferencing `btf_vmlinux`
as NULL. This patch fixes the following syzbot bug:

    https://syzkaller.appspot.com/bug?id=5edd146856fd513747c1992442732e5a0e9ba355

Reported-by: syzbot+ee09bda7017345f1fbe6@syzkaller.appspotmail.com
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
---
Thank you for reviewing my patch! I am new to Linux kernel development; would
the log message and errno be appropriate for this case?

Change in v2:
    - Split NULL and IS_ERR cases.

 kernel/bpf/btf.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 30721f2c2d10..092116a311f4 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4088,6 +4088,11 @@ static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn,
 	const char *tname, *sym;
 	u32 btf_id, i;
 
+	if (!btf_vmlinux) {
+		bpf_log(log, "btf_vmlinux doesn't exist\n");
+		return -EINVAL;
+	}
+
 	if (IS_ERR(btf_vmlinux)) {
 		bpf_log(log, "btf_vmlinux is malformed\n");
 		return -EINVAL;
-- 
2.25.1