Re: KASAN: slab-out-of-bounds Read in __nla_put_nohdr

From: Eric Dumazet
Date: Tue Jan 21 2020 - 14:55:37 EST

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On 1/21/20 11:47 AM, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 80892772 hsr: Fix a compilation error
> git tree: net
> console output: https://syzkaller.appspot.com/x/log.txt?x=1718e46ee00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d9290aeb7e6cf1c4
> dashboard link: https://syzkaller.appspot.com/bug?extid=5af9a90dad568aa9f611
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1043f521e00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10fb5521e00000
>
> Bisection is inconclusive: the bug happens on the oldest tested release.
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1084280de00000
> final crash: https://syzkaller.appspot.com/x/report.txt?x=1284280de00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1484280de00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+5af9a90dad568aa9f611@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> IPVS: ftp: loaded support on port[0] = 21
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:380 [inline]
> BUG: KASAN: slab-out-of-bounds in __nla_put_nohdr+0x46/0x50 lib/nlattr.c:815
> Read of size 12 at addr ffff888096ff0780 by task syz-executor696/9507
>
> CPU: 0 PID: 9507 Comm: syz-executor696 Not tainted 5.5.0-rc6-syzkaller #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+0x197/0x210 lib/dump_stack.c:118
> 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:639
> check_memory_region_inline mm/kasan/generic.c:185 [inline]
> check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
> memcpy+0x24/0x50 mm/kasan/common.c:125
> memcpy include/linux/string.h:380 [inline]
> __nla_put_nohdr+0x46/0x50 lib/nlattr.c:815
> nla_put_nohdr+0xf9/0x140 lib/nlattr.c:881
> tcf_em_tree_dump+0x67e/0x960 net/sched/ematch.c:471
> basic_dump+0x379/0x690 net/sched/cls_basic.c:308
> tcf_fill_node+0x58b/0x970 net/sched/cls_api.c:1814
> tfilter_notify+0x134/0x290 net/sched/cls_api.c:1840
> tc_new_tfilter+0xc18/0x2590 net/sched/cls_api.c:2108
> rtnetlink_rcv_msg+0x824/0xaf0 net/core/rtnetlink.c:5415
> netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
> rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5442
> netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
> netlink_unicast+0x58c/0x7d0 net/netlink/af_netlink.c:1328
> netlink_sendmsg+0x91c/0xea0 net/netlink/af_netlink.c:1917
> sock_sendmsg_nosec net/socket.c:639 [inline]
> sock_sendmsg+0xd7/0x130 net/socket.c:659
> ____sys_sendmsg+0x753/0x880 net/socket.c:2330
> ___sys_sendmsg+0x100/0x170 net/socket.c:2384
> __sys_sendmsg+0x105/0x1d0 net/socket.c:2417
> __do_sys_sendmsg net/socket.c:2426 [inline]
> __se_sys_sendmsg net/socket.c:2424 [inline]
> __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2424
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x440dd9
> Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 7b 10 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffd12f770f8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00000000004a25b0 RCX: 0000000000440dd9
> RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000000000003
> RBP: 00000000006cc018 R08: 0000000120080522 R09: 0000000120080522
> R10: 0000000120080522 R11: 0000000000000246 R12: 00000000004022e0
> R13: 0000000000402370 R14: 0000000000000000 R15: 0000000000000000
>
> Allocated by task 9507:
> save_stack+0x23/0x90 mm/kasan/common.c:72
> set_track mm/kasan/common.c:80 [inline]
> __kasan_kmalloc mm/kasan/common.c:513 [inline]
> __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
> kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
> __do_kmalloc mm/slab.c:3656 [inline]
> __kmalloc_track_caller+0x15f/0x760 mm/slab.c:3671
> kmemdup+0x27/0x60 mm/util.c:127
> kmemdup include/linux/string.h:453 [inline]
> em_nbyte_change+0xd6/0x150 net/sched/em_nbyte.c:32
> tcf_em_validate net/sched/ematch.c:241 [inline]
> tcf_em_tree_validate net/sched/ematch.c:359 [inline]
> tcf_em_tree_validate+0x9b5/0xf3c net/sched/ematch.c:300
> basic_set_parms net/sched/cls_basic.c:157 [inline]
> basic_change+0x513/0x14a0 net/sched/cls_basic.c:219
> tc_new_tfilter+0xbbd/0x2590 net/sched/cls_api.c:2104
> rtnetlink_rcv_msg+0x824/0xaf0 net/core/rtnetlink.c:5415
> netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
> rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5442
> netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
> netlink_unicast+0x58c/0x7d0 net/netlink/af_netlink.c:1328
> netlink_sendmsg+0x91c/0xea0 net/netlink/af_netlink.c:1917
> sock_sendmsg_nosec net/socket.c:639 [inline]
> sock_sendmsg+0xd7/0x130 net/socket.c:659
> ____sys_sendmsg+0x753/0x880 net/socket.c:2330
> ___sys_sendmsg+0x100/0x170 net/socket.c:2384
> __sys_sendmsg+0x105/0x1d0 net/socket.c:2417
> __do_sys_sendmsg net/socket.c:2426 [inline]
> __se_sys_sendmsg net/socket.c:2424 [inline]
> __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2424
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 4365:
> save_stack+0x23/0x90 mm/kasan/common.c:72
> set_track mm/kasan/common.c:80 [inline]
> kasan_set_free_info mm/kasan/common.c:335 [inline]
> __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
> kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
> __cache_free mm/slab.c:3426 [inline]
> kfree+0x10a/0x2c0 mm/slab.c:3757
> tomoyo_check_open_permission+0x19e/0x3e0 security/tomoyo/file.c:786
> tomoyo_file_open security/tomoyo/tomoyo.c:319 [inline]
> tomoyo_file_open+0xa9/0xd0 security/tomoyo/tomoyo.c:314
> security_file_open+0x71/0x300 security/security.c:1497
> do_dentry_open+0x37a/0x1380 fs/open.c:784
> vfs_open+0xa0/0xd0 fs/open.c:914
> do_last fs/namei.c:3356 [inline]
> path_openat+0x118b/0x3180 fs/namei.c:3473
> do_filp_open+0x1a1/0x280 fs/namei.c:3503
> do_sys_open+0x3fe/0x5d0 fs/open.c:1097
> __do_sys_open fs/open.c:1115 [inline]
> __se_sys_open fs/open.c:1110 [inline]
> __x64_sys_open+0x7e/0xc0 fs/open.c:1110
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff888096ff0780
> which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 0 bytes inside of
> 32-byte region [ffff888096ff0780, ffff888096ff07a0)
> The buggy address belongs to the page:
> page:ffffea00025bfc00 refcount:1 mapcount:0 mapping:ffff8880aa4001c0 index:0xffff888096ff0fc1
> raw: 00fffe0000000200 ffffea000253ec08 ffff8880aa401238 ffff8880aa4001c0
> raw: ffff888096ff0fc1 ffff888096ff0000 0000000100000030 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff888096ff0680: 00 00 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
> ffff888096ff0700: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>> ffff888096ff0780: 04 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
> ^
> ffff888096ff0800: 00 00 00 00 fc fc fc fc 00 00 00 00 fc fc fc fc
> ffff888096ff0880: 00 00 00 00 fc fc fc fc 00 00 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@xxxxxxxxxxxxxxxxx
>
> 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
>

em_nbyte_change() sets
em->datalen = sizeof(*nbyte) + nbyte->len;

But later tcf_em_validate() overwrites em->datalen with the user provide value (em->datalen = data_len; )
which can be bigger than the allocated (kmemdup) space in em_nbyte_change()

Should net/sched/em_nbyte.c() provide a dump() handler to avoid this issue ?

Next message: syzbot: "WARNING in cbq_destroy_class"
Previous message: Segher Boessenkool: "Re: GCC bug ? Re: [PATCH v2 10/10] powerpc/32s: Implement Kernel Userspace Access Protection"
In reply to: syzbot: "KASAN: slab-out-of-bounds Read in __nla_put_nohdr"
Next in thread: Cong Wang: "Re: KASAN: slab-out-of-bounds Read in __nla_put_nohdr"
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