Re: [syzbot] BUG: unable to handle kernel access to user memory in sock_ioctl

From: Dmitry Vyukov <dvyukov@google.com>
To: syzbot <syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv <linux-riscv@lists.infradead.org>
Cc: andrii@kernel.org, Alexei Starovoitov <ast@kernel.org>,
	bpf <bpf@vger.kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
	David Miller <davem@davemloft.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Martin KaFai Lau <kafai@fb.com>,
	kpsingh@kernel.org, Jakub Kicinski <kuba@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	netdev <netdev@vger.kernel.org>, Song Liu <songliubraving@fb.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Yonghong Song <yhs@fb.com>
Subject: Re: [syzbot] BUG: unable to handle kernel access to user memory in sock_ioctl
Date: Sun, 14 Mar 2021 11:01:39 +0100	[thread overview]
Message-ID: <CACT4Y+ZjVS+nOxtEByF5-djuhbCYLSDdZ7V04qJ0edpQR0514A@mail.gmail.com> (raw)
In-Reply-To: <CACT4Y+ZjdOaX_X530p+vPbG4mbtUuFsJ1v-gD24T4DnFUqcudA@mail.gmail.com>

On Wed, Mar 10, 2021 at 7:53 PM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Wed, Mar 10, 2021 at 7:28 PM syzbot
> <syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    0d7588ab riscv: process: Fix no prototype for arch_dup_tas..
> > git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
> > console output: https://syzkaller.appspot.com/x/log.txt?x=122c343ad00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=e3c595255fb2d136
> > dashboard link: https://syzkaller.appspot.com/bug?extid=c23c5421600e9b454849
> > userspace arch: riscv64
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com
>
> +riscv maintainers
>
> Another case of put_user crashing.

There are 58 crashes in sock_ioctl already. Somehow there is a very
significant skew towards crashing with this "user memory without
uaccess routines" in schedule_tail and sock_ioctl of all places in the
kernel that use put_user... This looks very strange... Any ideas
what's special about these 2 locations?

> > Unable to handle kernel access to user memory without uaccess routines at virtual address 0000000020000300
> > Oops [#1]
> > Modules linked in:
> > CPU: 1 PID: 4488 Comm: syz-executor.0 Not tainted 5.12.0-rc2-syzkaller-00467-g0d7588ab9ef9 #0
> > Hardware name: riscv-virtio,qemu (DT)
> > epc : sock_ioctl+0x424/0x6ac net/socket.c:1124
> >  ra : sock_ioctl+0x424/0x6ac net/socket.c:1124
> > epc : ffffffe002aeeb3e ra : ffffffe002aeeb3e sp : ffffffe023867da0
> >  gp : ffffffe005d25378 tp : ffffffe007e116c0 t0 : 0000000000000000
> >  t1 : 0000000000000001 t2 : 0000003fb8035e44 s0 : ffffffe023867e30
> >  s1 : 0000000000040000 a0 : 0000000000000000 a1 : 0000000000000007
> >  a2 : 1ffffffc00fc22d8 a3 : ffffffe003bc1d02 a4 : 0000000000000000
> >  a5 : 0000000000000000 a6 : 0000000000f00000 a7 : ffffffe000082eba
> >  s2 : 0000000000000000 s3 : 0000000000008902 s4 : 0000000020000300
> >  s5 : ffffffe005d2b0d0 s6 : ffffffe010facfc0 s7 : ffffffe008e00000
> >  s8 : 0000000000008903 s9 : ffffffe010fad080 s10: 0000000000000000
> >  s11: 0000000000020000 t3 : 982de389919f6300 t4 : ffffffc401175688
> >  t5 : ffffffc401175691 t6 : 0000000000000007
> > status: 0000000000000120 badaddr: 0000000020000300 cause: 000000000000000f
> > Call Trace:
> > [<ffffffe002aeeb3e>] sock_ioctl+0x424/0x6ac net/socket.c:1124
> > [<ffffffe0003fdb6a>] vfs_ioctl fs/ioctl.c:48 [inline]
> > [<ffffffe0003fdb6a>] __do_sys_ioctl fs/ioctl.c:753 [inline]
> > [<ffffffe0003fdb6a>] sys_ioctl+0x5c2/0xd56 fs/ioctl.c:739
> > [<ffffffe000005562>] ret_from_syscall+0x0/0x2
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > ---[ end trace a5f91e70f37b907b ]---
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.