Date:   Thu, 23 Jan 2020 15:35:19 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     syzbot <syzbot+35d4dea36c387813ed31@...kaller.appspotmail.com>,
        adobriyan@...il.com, davem@...emloft.net, dsahern@...il.com,
        ja@....bg, jhs@...atatu.com, jiri@...nulli.us,
        johannes@...solutions.net, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tgraf@...g.ch, xiyou.wangcong@...il.com
Subject: Re: KASAN: slab-out-of-bounds Read in tcf_exts_destroy



On 1/23/20 3:27 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    569aad4f net: ag71xx: fix mdio subnode support
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=1591b415600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6ffbfa7e4a36190f
> dashboard link: https://syzkaller.appspot.com/bug?extid=35d4dea36c387813ed31
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120c47f5600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d58ceb600000
> 
> The bug was bisected to:
> 
> commit 6e237d099fac1f73a7b6d7287bb9191f29585a4e
> Author: David Ahern <dsahern@...il.com>
> Date:   Thu Dec 7 04:09:12 2017 +0000
> 
>     netlink: Relax attr validation for fixed length types
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=152f5e43600000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=172f5e43600000
> console output: https://syzkaller.appspot.com/x/log.txt?x=132f5e43600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+35d4dea36c387813ed31@...kaller.appspotmail.com
> Fixes: 6e237d099fac ("netlink: Relax attr validation for fixed length types")
> 
> netlink: 'syz-executor879': attribute type 2 has an invalid length.
> netlink: 'syz-executor879': attribute type 2 has an invalid length.
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in tcf_exts_destroy+0xb3/0xd0 net/sched/cls_api.c:2897
> Read of size 8 at addr ffff8880a1463790 by task syz-executor879/9050
> 
> CPU: 0 PID: 9050 Comm: syz-executor879 Not tainted 5.3.0+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
>  print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
>  __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
>  kasan_report+0x12/0x20 mm/kasan/common.c:634
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
>  tcf_exts_destroy+0xb3/0xd0 net/sched/cls_api.c:2897
>  tcindex_free_perfect_hash.isra.0+0xb3/0x150 net/sched/cls_tcindex.c:273
>  tcindex_set_parms+0x1107/0x1e50 net/sched/cls_tcindex.c:484
>  tcindex_change+0x230/0x320 net/sched/cls_tcindex.c:519
>  tc_new_tfilter+0xa4b/0x1c70 net/sched/cls_api.c:2019
>  rtnetlink_rcv_msg+0x838/0xb00 net/core/rtnetlink.c:5214
>  netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
>  rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5241
>  netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
>  netlink_unicast+0x531/0x710 net/netlink/af_netlink.c:1328
>  netlink_sendmsg+0x8a5/0xd60 net/netlink/af_netlink.c:1917
>  sock_sendmsg_nosec net/socket.c:637 [inline]
>  sock_sendmsg+0xd7/0x130 net/socket.c:657
>  ___sys_sendmsg+0x3e2/0x920 net/socket.c:2311
>  __sys_sendmmsg+0x1bf/0x4d0 net/socket.c:2413
>  __do_sys_sendmmsg net/socket.c:2442 [inline]
>  __se_sys_sendmmsg net/socket.c:2439 [inline]
>  __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2439
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x443299
> Code: e8 9c 07 03 00 48 83 c4 18 c3 0f 1f 80 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 0f 83 3b 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffde8f54e48 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443299
> RDX: 0000000000000332 RSI: 0000000020000140 RDI: 0000000000000008
> RBP: 000000000000000c R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0030766461746162
> R13: 00000000004041f0 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 9050:
>  save_stack+0x23/0x90 mm/kasan/common.c:69
>  set_track mm/kasan/common.c:77 [inline]
>  __kasan_kmalloc mm/kasan/common.c:510 [inline]
>  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
>  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
>  __do_kmalloc mm/slab.c:3655 [inline]
>  __kmalloc+0x163/0x770 mm/slab.c:3664
>  kmalloc_array include/linux/slab.h:614 [inline]
>  kcalloc include/linux/slab.h:625 [inline]
>  tcindex_alloc_perfect_hash+0x5a/0x320 net/sched/cls_tcindex.c:281
>  tcindex_set_parms+0x454/0x1e50 net/sched/cls_tcindex.c:339
>  tcindex_change+0x230/0x320 net/sched/cls_tcindex.c:519
>  tc_new_tfilter+0xa4b/0x1c70 net/sched/cls_api.c:2019
>  rtnetlink_rcv_msg+0x838/0xb00 net/core/rtnetlink.c:5214
>  netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
>  rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5241
>  netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
>  netlink_unicast+0x531/0x710 net/netlink/af_netlink.c:1328
>  netlink_sendmsg+0x8a5/0xd60 net/netlink/af_netlink.c:1917
>  sock_sendmsg_nosec net/socket.c:637 [inline]
>  sock_sendmsg+0xd7/0x130 net/socket.c:657
>  ___sys_sendmsg+0x3e2/0x920 net/socket.c:2311
>  __sys_sendmmsg+0x1bf/0x4d0 net/socket.c:2413
>  __do_sys_sendmmsg net/socket.c:2442 [inline]
>  __se_sys_sendmmsg net/socket.c:2439 [inline]
>  __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2439
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 2660:
>  save_stack+0x23/0x90 mm/kasan/common.c:69
>  set_track mm/kasan/common.c:77 [inline]
>  kasan_set_free_info mm/kasan/common.c:332 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:471
>  kasan_slab_free+0xe/0x10 mm/kasan/common.c:480
>  __cache_free mm/slab.c:3425 [inline]
>  kfree+0x10a/0x2c0 mm/slab.c:3756
>  call_usermodehelper_freeinfo kernel/umh.c:48 [inline]
>  umh_complete kernel/umh.c:62 [inline]
>  umh_complete+0x8d/0xa0 kernel/umh.c:51
>  call_usermodehelper_exec_async+0x46c/0x730 kernel/umh.c:122
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> 
> The buggy address belongs to the object at ffff8880a1463700
>  which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 144 bytes inside of
>  192-byte region [ffff8880a1463700, ffff8880a14637c0)
> The buggy address belongs to the page:
> page:ffffea00028518c0 refcount:1 mapcount:0 mapping:ffff8880aa400000 index:0x0
> flags: 0x1fffc0000000200(slab)
> raw: 01fffc0000000200 ffffea000287e608 ffffea000286ff48 ffff8880aa400000
> raw: 0000000000000000 ffff8880a1463000 0000000100000010 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880a1463680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8880a1463700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ffff8880a1463780: 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>                          ^
>  ffff8880a1463800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880a1463880: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ==================================================================
> 
> 
> ---
> This bug 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@...glegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 


tcindex_set_parms() seems buggy :

After

if (tcindex_alloc_perfect_hash(net, cp) < 0) // line 339

it can overwrite cp->hash : 

if (tb[TCA_TCINDEX_HASH])
    cp->hash = nla_get_u32(tb[TCA_TCINDEX_HASH]);

Meaning that out-of-bounds might happen later.

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