RE: KASAN: use-after-free Read in tipc_group_size

From: Jon Maloy
Date: Mon Jan 08 2018 - 15:11:50 EST

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> -----Original Message-----
> From: Cong Wang [mailto:xiyou.wangcong@xxxxxxxxx]
> Sent: Monday, January 08, 2018 13:44
> To: syzbot <syzbot+aae58876fb5a1fad0a4b@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Cc: David Miller <davem@xxxxxxxxxxxxx>; Jon Maloy
> <jon.maloy@xxxxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Linux
> Kernel Network Developers <netdev@xxxxxxxxxxxxxxx>; syzkaller-
> bugs@xxxxxxxxxxxxxxxx; tipc-discussion@xxxxxxxxxxxxxxxxxxxxx; Ying Xue
> <ying.xue@xxxxxxxxxxxxx>
> Subject: Re: KASAN: use-after-free Read in tipc_group_size
>
> On Mon, Jan 8, 2018 at 6:58 AM, syzbot
> <syzbot+aae58876fb5a1fad0a4b@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > Hello,
> >
> > syzkaller hit the following crash on
> > b2cd1df66037e7c4697c7e40496bf7e4a5e16a2d
> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.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+aae58876fb5a1fad0a4b@xxxxxxxxxxxxxxxxxxxxxxxxx
> > 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_size+0x40/0x50
> > net/tipc/group.c:158 Read of size 2 at addr ffff8801c08ba280 by task
> > syzkaller447710/3513
> >
> > CPU: 0 PID: 3513 Comm: syzkaller447710 Not tainted 4.15.0-rc7+ #252
> > 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_load2_noabort+0x14/0x20 mm/kasan/report.c:428
> > tipc_group_size+0x40/0x50 net/tipc/group.c:158
> > tipc_poll+0x374/0x4f0 net/tipc/socket.c:739
>
> Seems we have to lock the sock for tipc_group_size() in tipc_poll().

Not quite. I think it is that we initialize 'grp' on the stack before we call sock_poll_wait() and access it after it returns.
This is anyway fixed in patch #9 of the series I just sent to net-next, where the poll() handling for group members is redesigned.

///jon

>
>
> > sock_poll+0x141/0x320 net/socket.c:1117 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: 0033:0x445cb9
> > RSP: 002b:00007f04886b1ce8 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000007
> > RAX: ffffffffffffffda RBX: 00000000006dac3c RCX: 0000000000445cb9
> > RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000020fa2ff8
> > RBP: 00000000006dac38 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ffc84d56d7f R14: 00007f04886b29c0 R15: 0000000000000005
> >
> > Allocated by task 3510:
> > 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+0x116/0x9c0 net/tipc/group.c:167 tipc_sk_join
> > net/tipc/socket.c:2747 [inline]
> > tipc_setsockopt+0x249/0xc10 net/tipc/socket.c:2861 SYSC_setsockopt
> > net/socket.c:1829 [inline]
> > SyS_setsockopt+0x189/0x360 net/socket.c:1808
> > entry_SYSCALL_64_fastpath+0x23/0x9a
> >
> > Freed by task 3510:
> > 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:206 tipc_sk_join
> > net/tipc/socket.c:2760 [inline]
> > tipc_setsockopt+0xb0d/0xc10 net/tipc/socket.c:2861 SYSC_setsockopt
> > net/socket.c:1829 [inline]
> > SyS_setsockopt+0x189/0x360 net/socket.c:1808
> > entry_SYSCALL_64_fastpath+0x23/0x9a
> >
> > The buggy address belongs to the object at ffff8801c08ba200 which
> > belongs to the cache kmalloc-192 of size 192 The buggy address is
> > located 128 bytes inside of 192-byte region [ffff8801c08ba200,
> > ffff8801c08ba2c0) The buggy address belongs to the page:
> > page:ffffea0007022e80 count:1 mapcount:0 mapping:ffff8801c08ba000
> > index:0x0
> > flags: 0x2fffc0000000100(slab)
> > raw: 02fffc0000000100 ffff8801c08ba000 0000000000000000
> > 0000000100000010
> > raw: ffffea00071338a0 ffffea0006fe2360 ffff8801dac00040
> > 0000000000000000 page dumped because: kasan: bad access detected
> >
> > Memory state around the buggy address:
> > ffff8801c08ba180: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> > ffff8801c08ba200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >>
> >> ffff8801c08ba280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> >
> > ^
> > ffff8801c08ba300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8801c08ba380: fb fb fb fb fb fb fb fb 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@xxxxxxxxxxxxxxxxx
> >
> > 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.
> > Note: all commands must start from beginning of the line in the email body.

Next message: Sean Paul: "Re: [PATCH v6 0/9] drm/i915: Implement HDCP"
Previous message: Pavel Machek: "[PATCH] clarify how insecure CPU is"
In reply to: Cong Wang: "Re: KASAN: use-after-free Read in tipc_group_size"
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