Date:   Tue, 16 Jan 2018 13:23:39 +0000
From:   Jon Maloy <jon.maloy@...csson.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        syzbot <syzbot+799dafde0286795858ac@...kaller.appspotmail.com>
CC:     David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        Ying Xue <ying.xue@...driver.com>
Subject: RE: KASAN: use-after-free Read in tipc_group_is_open



> -----Original Message-----
> From: Cong Wang [mailto:xiyou.wangcong@...il.com]
> Sent: Monday, January 15, 2018 23:44
> To: syzbot <syzbot+799dafde0286795858ac@...kaller.appspotmail.com>
> Cc: David Miller <davem@...emloft.net>; Jon Maloy
> <jon.maloy@...csson.com>; LKML <linux-kernel@...r.kernel.org>; Linux
> Kernel Network Developers <netdev@...r.kernel.org>; syzkaller-
> bugs@...glegroups.com; tipc-discussion@...ts.sourceforge.net; Ying Xue
> <ying.xue@...driver.com>
> Subject: Re: KASAN: use-after-free Read in tipc_group_is_open
> 
> On Mon, Jan 15, 2018 at 7:58 PM, syzbot
> <syzbot+799dafde0286795858ac@...kaller.appspotmail.com> wrote:
> > Hello,
> >
> > syzkaller hit the following crash on
> > 594831a8aba3fd045c3212a3e3bb9788c77b989d
> > git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/maste
> > r
> > compiler: gcc (GCC) 7.1.1 20170620
> > .config is attached
> > Raw console output is attached.
> > C reproducer is attached
> > syzkaller reproducer is attached. See https://goo.gl/kgGztJ for
> > information about syzkaller reproducers
> >
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+799dafde0286795858ac@...kaller.appspotmail.com
> > It will help syzbot understand when the bug is fixed. See footer for
> > details.
> > If you forward the report, please keep this part and the footer.
> >
> >
> ==========================================================
> ========
> > BUG: KASAN: use-after-free in tipc_group_is_open+0x3a/0x40
> > net/tipc/group.c:106
> > Read of size 1 at addr ffff8801d89f7378 by task syzkaller275009/3704
> >
> > CPU: 0 PID: 3704 Comm: syzkaller275009 Not tainted 4.15.0-rc7+ #190
> > Hardware name: Google Google Compute Engine/Google Compute Engine,
> > BIOS Google 01/01/2011 Call Trace:
> >  __dump_stack lib/dump_stack.c:17 [inline]
> >  dump_stack+0x194/0x257 lib/dump_stack.c:53
> >  print_address_description+0x73/0x250 mm/kasan/report.c:252
> > kasan_report_error mm/kasan/report.c:351 [inline]
> >  kasan_report+0x25b/0x340 mm/kasan/report.c:409
> >  __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:427
> >  tipc_group_is_open+0x3a/0x40 net/tipc/group.c:106
> >  tipc_poll+0x364/0x4d0 net/tipc/socket.c:740
> 
> 
> commit eb929a91b213d2a72c5a8b4af9a1acf63bfb8287
> Author: Jon Maloy <jon.maloy@...csson.com>
> Date:   Mon Jan 8 21:03:31 2018 +0100
> 
>     tipc: improve poll() for group member socket
> 
> Apparently Jon's commit doesn't fix this. I also don't understand why Jon
> believes sock_poll_wait() could sync with setsockopt path...

While sock_poll_wait() is sleeping, it is possible that the item the 'grp' stack variable is pointing to might be deleted, invalidating the pointer.
This is why I moved the initialization of the pointer to after sock_poll_wait().
However, now tipc_sock->group is clearly set to NULL at both locations where a group item might be deleted, so the reason for the warning must be something else.
I am open to suggestions.

///jon

> 
> 
> 
> >  sock_poll+0x141/0x320 net/socket.c:1111  do_pollfd fs/select.c:822
> > [inline]  do_poll fs/select.c:872 [inline]
> >  do_sys_poll+0x715/0x10b0 fs/select.c:966  SYSC_poll fs/select.c:1024
> > [inline]
> >  SyS_poll+0x10d/0x450 fs/select.c:1012
> > entry_SYSCALL_64_fastpath+0x23/0x9a
> > RIP: 0033:0x446129
> > RSP: 002b:00007f0f2df96db8 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000007
> > RAX: ffffffffffffffda RBX: 00000000006dbc54 RCX: 0000000000446129
> > RDX: 0000000000007fff RSI: 000000000000000a RDI: 0000000020ef5000
> > RBP: 00000000006dbc50 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ffc07e2923f R14: 00007f0f2df979c0 R15: 0000000000000007
> >
> > Allocated by task 3702:
> >  save_stack+0x43/0xd0 mm/kasan/kasan.c:447  set_track
> > mm/kasan/kasan.c:459 [inline]
> >  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
> >  kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610  kmalloc
> > include/linux/slab.h:499 [inline]  kzalloc include/linux/slab.h:688
> > [inline]
> >  tipc_group_create+0x144/0x900 net/tipc/group.c:180  tipc_sk_join
> > net/tipc/socket.c:2762 [inline]
> >  tipc_setsockopt+0x274/0xce0 net/tipc/socket.c:2877  SYSC_setsockopt
> > net/socket.c:1823 [inline]
> >  SyS_setsockopt+0x189/0x360 net/socket.c:1802
> > entry_SYSCALL_64_fastpath+0x23/0x9a
> >
> > Freed by task 3702:
> >  save_stack+0x43/0xd0 mm/kasan/kasan.c:447  set_track
> > mm/kasan/kasan.c:459 [inline]
> >  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524  __cache_free
> > mm/slab.c:3488 [inline]
> >  kfree+0xd6/0x260 mm/slab.c:3803
> >  tipc_group_delete+0x2c8/0x3d0 net/tipc/group.c:234  tipc_sk_join
> > net/tipc/socket.c:2775 [inline]
> >  tipc_setsockopt+0xaa9/0xce0 net/tipc/socket.c:2877  SYSC_setsockopt
> > net/socket.c:1823 [inline]
> >  SyS_setsockopt+0x189/0x360 net/socket.c:1802
> > entry_SYSCALL_64_fastpath+0x23/0x9a
> >
> > The buggy address belongs to the object at ffff8801d89f7300  which
> > belongs to the cache kmalloc-128 of size 128 The buggy address is
> > located 120 bytes inside of  128-byte region [ffff8801d89f7300,
> > ffff8801d89f7380) The buggy address belongs to the page:
> > page:ffffea0007627dc0 count:1 mapcount:0 mapping:ffff8801d89f7000
> > index:0x0
> > flags: 0x2fffc0000000100(slab)
> > raw: 02fffc0000000100 ffff8801d89f7000 0000000000000000
> > 0000000100000015
> > raw: ffffea0007622720 ffffea0007627ce0 ffff8801dac00640
> > 0000000000000000 page dumped because: kasan: bad access detected
> >
> > Memory state around the buggy address:
> >  ffff8801d89f7200: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> >  ffff8801d89f7280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> >>
> >> ffff8801d89f7300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >
> >                                                                 ^
> >  ffff8801d89f7380: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
> >  ffff8801d89f7400: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> >
> ==========================================================
> ========
> >
> >
> > ---
> > This bug is generated by a dumb bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for details.
> > Direct all questions to syzkaller@...glegroups.com.
> >
> > syzbot will keep track of this bug report.
> > If you forgot to add the Reported-by tag, once the fix for this bug is
> > merged into any tree, please reply to this email with:
> > #syz fix: exact-commit-title
> > If you want to test a patch for this bug, please reply with:
> > #syz test: git://repo/address.git branch and provide the patch inline
> > or as an attachment.
> > To mark this as a duplicate of another syzbot report, please reply with:
> > #syz dup: exact-subject-of-another-report If it's a one-off invalid
> > bug report, please reply with:
> > #syz invalid
> > Note: if the crash happens again, it will cause creation of a new bug
> > report.
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