Re: [syzbot] BUG: sleeping function called from invalid context in _copy_to_iter

[Eric Dumazet]

On Mon, Aug 9, 2021 at 10:02 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Mon, Aug 9, 2021 at 9:40 PM Shoaib Rao <rao.shoaib@xxxxxxxxxx> wrote:
> >
> >
> > On 8/9/21 12:21 PM, Dmitry Vyukov wrote:
> > > On Mon, 9 Aug 2021 at 21:16, Shoaib Rao <rao.shoaib@xxxxxxxxxx> wrote:
> > >> On 8/9/21 11:06 AM, Dmitry Vyukov wrote:
> > >>> On Mon, 9 Aug 2021 at 19:33, Shoaib Rao <rao.shoaib@xxxxxxxxxx> wrote:
> > >>>> This seems like a false positive. 1) The function will not sleep because
> > >>>> it only calls copy routine if the byte is present. 2). There is no
> > >>>> difference between this new call and the older calls in
> > >>>> unix_stream_read_generic().
> > >>> Hi Shoaib,
> > >>>
> > >>> Thanks for looking into this.
> > >>> Do you have any ideas on how to fix this tool's false positive? Tools
> > >>> with false positives are order of magnitude less useful than tools w/o
> > >>> false positives. E.g. do we turn it off on syzbot? But I don't
> > >>> remember any other false positives from "sleeping function called from
> > >>> invalid context" checker...
> > >> Before we take any action I would like to understand why the tool does
> > >> not single out other calls to recv_actor in unix_stream_read_generic().
> > >> The context in all cases is the same. I also do not understand why the
> > >> code would sleep, Let's assume the user provided address is bad, the
> > >> code will return EFAULT, it will never sleep,
> > > I always assumed that it's because if user pages are swapped out, it
> > > may need to read them back from disk.
> >
> > Page faults occur all the time, the page may not even be in the cache or
> > the mapping is not there (mmap), so I would not consider this a bug. The
> > code should complain about all other calls as they are also copying  to
> > user pages. I must not be following some semantics for the code to be
> > triggered but I can not figure that out. What is the recommended
> > interface to do user copy from kernel?
>
> Are you aware of the difference between a mutex and a spinlock ?
>
> When copying data from/to user, you can not hold a spinlock.
>
>

I am guessing that even your test would trigger the warning,
if you make sure to include CONFIG_DEBUG_ATOMIC_SLEEP=y in your kernel build.

> >
> > Shoaib
> >
> > >
> > >> if the kernel provided
> > >> address is bad the system will panic. The only difference I see is that
> > >> the new code holds 2 locks while the previous code held one lock, but
> > >> the locks are acquired before the call to copy.
> > >>
> > >> So please help me understand how the tool works. Even though I have
> > >> evaluated the code carefully, there is always a possibility that the
> > >> tool is correct.
> > >>
> > >> Shoaib
> > >>
> > >>>
> > >>>
> > >>>> On 8/8/21 4:38 PM, syzbot wrote:
> > >>>>> Hello,
> > >>>>>
> > >>>>> syzbot found the following issue on:
> > >>>>>
> > >>>>> HEAD commit:    c2eecaa193ff pktgen: Remove redundant clone_skb override
> > >>>>> git tree:       net-next
> > >>>>> console output: https://urldefense.com/v3/__https://syzkaller.appspot.com/x/log.txt?x=12e3a69e300000__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPHEdQcWD$
> > >>>>> kernel config:  https://urldefense.com/v3/__https://syzkaller.appspot.com/x/.config?x=aba0c23f8230e048__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPLGp1-Za$
> > >>>>> dashboard link: https://urldefense.com/v3/__https://syzkaller.appspot.com/bug?extid=8760ca6c1ee783ac4abd__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPCORTNOH$
> > >>>>> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> > >>>>> syz repro:      https://urldefense.com/v3/__https://syzkaller.appspot.com/x/repro.syz?x=15c5b104300000__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPAjhi2yc$
> > >>>>> C reproducer:   https://urldefense.com/v3/__https://syzkaller.appspot.com/x/repro.c?x=10062aaa300000__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPNzAjzQJ$
> > >>>>>
> > >>>>> The issue was bisected to:
> > >>>>>
> > >>>>> commit 314001f0bf927015e459c9d387d62a231fe93af3
> > >>>>> Author: Rao Shoaib <rao.shoaib@xxxxxxxxxx>
> > >>>>> Date:   Sun Aug 1 07:57:07 2021 +0000
> > >>>>>
> > >>>>>        af_unix: Add OOB support
> > >>>>>
> > >>>>> bisection log:  https://urldefense.com/v3/__https://syzkaller.appspot.com/x/bisect.txt?x=10765f8e300000__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPK2iWt2r$
> > >>>>> final oops:     https://urldefense.com/v3/__https://syzkaller.appspot.com/x/report.txt?x=12765f8e300000__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPKAb0dft$
> > >>>>> console output: https://urldefense.com/v3/__https://syzkaller.appspot.com/x/log.txt?x=14765f8e300000__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPNlW_w-u$
> > >>>>>
> > >>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > >>>>> Reported-by: syzbot+8760ca6c1ee783ac4abd@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >>>>> Fixes: 314001f0bf92 ("af_unix: Add OOB support")
> > >>>>>
> > >>>>> BUG: sleeping function called from invalid context at lib/iov_iter.c:619
> > >>>>> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 8443, name: syz-executor700
> > >>>>> 2 locks held by syz-executor700/8443:
> > >>>>>     #0: ffff888028fa0d00 (&u->iolock){+.+.}-{3:3}, at: unix_stream_read_generic+0x16c6/0x2190 net/unix/af_unix.c:2501
> > >>>>>     #1: ffff888028fa0df0 (&u->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
> > >>>>>     #1: ffff888028fa0df0 (&u->lock){+.+.}-{2:2}, at: unix_stream_read_generic+0x16d0/0x2190 net/unix/af_unix.c:2502
> > >>>>> Preemption disabled at:
> > >>>>> [<0000000000000000>] 0x0
> > >>>>> CPU: 1 PID: 8443 Comm: syz-executor700 Not tainted 5.14.0-rc3-syzkaller #0
> > >>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > >>>>> Call Trace:
> > >>>>>     __dump_stack lib/dump_stack.c:88 [inline]
> > >>>>>     dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
> > >>>>>     ___might_sleep.cold+0x1f1/0x237 kernel/sched/core.c:9154
> > >>>>>     __might_fault+0x6e/0x180 mm/memory.c:5258
> > >>>>>     _copy_to_iter+0x199/0x1600 lib/iov_iter.c:619
> > >>>>>     copy_to_iter include/linux/uio.h:139 [inline]
> > >>>>>     simple_copy_to_iter+0x4c/0x70 net/core/datagram.c:519
> > >>>>>     __skb_datagram_iter+0x10f/0x770 net/core/datagram.c:425
> > >>>>>     skb_copy_datagram_iter+0x40/0x50 net/core/datagram.c:533
> > >>>>>     skb_copy_datagram_msg include/linux/skbuff.h:3620 [inline]
> > >>>>>     unix_stream_read_actor+0x78/0xc0 net/unix/af_unix.c:2701
> > >>>>>     unix_stream_recv_urg net/unix/af_unix.c:2433 [inline]
> > >>>>>     unix_stream_read_generic+0x17cd/0x2190 net/unix/af_unix.c:2504
> > >>>>>     unix_stream_recvmsg+0xb1/0xf0 net/unix/af_unix.c:2717
> > >>>>>     sock_recvmsg_nosec net/socket.c:944 [inline]
> > >>>>>     sock_recvmsg net/socket.c:962 [inline]
> > >>>>>     sock_recvmsg net/socket.c:958 [inline]
> > >>>>>     ____sys_recvmsg+0x2c4/0x600 net/socket.c:2622
> > >>>>>     ___sys_recvmsg+0x127/0x200 net/socket.c:2664
> > >>>>>     do_recvmmsg+0x24d/0x6d0 net/socket.c:2758
> > >>>>>     __sys_recvmmsg net/socket.c:2837 [inline]
> > >>>>>     __do_sys_recvmmsg net/socket.c:2860 [inline]
> > >>>>>     __se_sys_recvmmsg net/socket.c:2853 [inline]
> > >>>>>     __x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2853
> > >>>>>     do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > >>>>>     do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > >>>>>     entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >>>>> RIP: 0033:0x43ef39
> > >>>>> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> > >>>>> RSP: 002b:00007ffca8776d68 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> > >>>>> RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043ef39
> > >>>>> RDX: 0000000000000700 RSI: 0000000020001140 RDI: 0000000000000004
> > >>>>> RBP: 0000000000402f20 R08: 0000000000000000 R09: 0000000000400488
> > >>>>> R10: 0000000000000007 R11: 0000000000000246 R12: 0000000000402fb0
> > >>>>> R13: 0000000000000000 R14: 00000000004ac018 R15: 0000000000400488
> > >>>>>
> > >>>>> =============================
> > >>>>> [ BUG: Invalid wait context ]
> > >>>>> 5.14.0-rc3-syzkaller #0 Tainted: G        W
> > >>>>> -----------------------------
> > >>>>> syz-executor700/8443 is trying to lock:
> > >>>>> ffff8880212b6a28 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0xa3/0x180 mm/memory.c:5260
> > >>>>> other info that might help us debug this:
> > >>>>> context-{4:4}
> > >>>>> 2 locks held by syz-executor700/8443:
> > >>>>>     #0: ffff888028fa0d00 (&u->iolock){+.+.}-{3:3}, at: unix_stream_read_generic+0x16c6/0x2190 net/unix/af_unix.c:2501
> > >>>>>     #1: ffff888028fa0df0 (&u->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
> > >>>>>     #1: ffff888028fa0df0 (&u->lock){+.+.}-{2:2}, at: unix_stream_read_generic+0x16d0/0x2190 net/unix/af_unix.c:2502
> > >>>>> stack backtrace:
> > >>>>> CPU: 1 PID: 8443 Comm: syz-executor700 Tainted: G        W         5.14.0-rc3-syzkaller #0
> > >>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > >>>>> Call Trace:
> > >>>>>     __dump_stack lib/dump_stack.c:88 [inline]
> > >>>>>     dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
> > >>>>>     print_lock_invalid_wait_context kernel/locking/lockdep.c:4666 [inline]
> > >>>>>     check_wait_context kernel/locking/lockdep.c:4727 [inline]
> > >>>>>     __lock_acquire.cold+0x213/0x3ab kernel/locking/lockdep.c:4965
> > >>>>>     lock_acquire kernel/locking/lockdep.c:5625 [inline]
> > >>>>>     lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
> > >>>>>     __might_fault mm/memory.c:5261 [inline]
> > >>>>>     __might_fault+0x106/0x180 mm/memory.c:5246
> > >>>>>     _copy_to_iter+0x199/0x1600 lib/iov_iter.c:619
> > >>>>>     copy_to_iter include/linux/uio.h:139 [inline]
> > >>>>>     simple_copy_to_iter+0x4c/0x70 net/core/datagram.c:519
> > >>>>>     __skb_datagram_iter+0x10f/0x770 net/core/datagram.c:425
> > >>>>>     skb_copy_datagram_iter+0x40/0x50 net/core/datagram.c:533
> > >>>>>     skb_copy_datagram_msg include/linux/skbuff.h:3620 [inline]
> > >>>>>     unix_stream_read_actor+0x78/0xc0 net/unix/af_unix.c:2701
> > >>>>>     unix_stream_recv_urg net/unix/af_unix.c:2433 [inline]
> > >>>>>     unix_stream_read_generic+0x17cd/0x2190 net/unix/af_unix.c:2504
> > >>>>>     unix_stream_recvmsg+0xb1/0xf0 net/unix/af_unix.c:2717
> > >>>>>     sock_recvmsg_nosec net/socket.c:944 [inline]
> > >>>>>     sock_recvmsg net/socket.c:962 [inline]
> > >>>>>     sock_recvmsg net/socket.c:958 [inline]
> > >>>>>     ____sys_recvmsg+0x2c4/0x600 net/socket.c:2622
> > >>>>>     ___sys_recvmsg+0x127/0x200 net/socket.c:2664
> > >>>>>     do_recvmmsg+0x24d/0x6d0 net/socket.c:2758
> > >>>>>     __sys_recvmmsg net/socket.c:2837 [inline]
> > >>>>>     __do_sys_recvmmsg net/socket.c:2860 [inline]
> > >>>>>     __se_sys_recvmmsg net/socket.c:2853 [inline]
> > >>>>>     __x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2853
> > >>>>>     do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > >>>>>     do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > >>>>>     entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >>>>> RIP: 0033:0x43ef39
> > >>>>> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> > >>>>> RSP: 002b:00007ffca8776d68 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
> > >>>>> RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043ef39
> > >>>>> RDX: 0000000000000700 RSI: 0000000020001140 RDI: 0000000000000004
> > >>>>> RBP: 0000000000402f20 R08: 0000000000000000 R09: 0000000000400488
> > >>>>> R10: 0000000000000007 R11: 0000000000000246 R12: 0000
> > >>>>>
> > >>>>>
> > >>>>> ---
> > >>>>> This report is generated by a bot. It may contain errors.
> > >>>>> See https://urldefense.com/v3/__https://goo.gl/tpsmEJ__;!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPG1UhbpZ$  for more information about syzbot.
> > >>>>> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> > >>>>>
> > >>>>> syzbot will keep track of this issue. See:
> > >>>>> https://urldefense.com/v3/__https://goo.gl/tpsmEJ*status__;Iw!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPKlEx5v1$  for how to communicate with syzbot.
> > >>>>> For information about bisection process see: https://urldefense.com/v3/__https://goo.gl/tpsmEJ*bisection__;Iw!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPJk7KaIr$
> > >>>>> syzbot can test patches for this issue, for details see:
> > >>>>> https://urldefense.com/v3/__https://goo.gl/tpsmEJ*testing-patches__;Iw!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPMhq2hD3$
> > >>>> --
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> > >>>> To view this discussion on the web visit https://urldefense.com/v3/__https://groups.google.com/d/msgid/syzkaller-bugs/0c106e6c-672f-474e-5815-97b65596139d*40oracle.com__;JQ!!ACWV5N9M2RV99hQ!fbn9ny5Bw51Jl6yrU93iULDBXa_DPjyVIgQuZWyQbCo5IRkAzvYs6JKlPHjmYAGZ$ .