Re: BUG: bad usercopy in __check_heap_object (3)

[Eric Biggers]

On Fri, Jul 06, 2018 at 03:39:04PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    526674536360 Add linux-next specific files for 20180706
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=12d51a2c400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c8d1cfc0cb798e48
> dashboard link: https://syzkaller.appspot.com/bug?extid=4b712dce5cbce6700f27
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=14b05afc400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17594968400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+4b712dce5cbce6700f27@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> IPv6: ADDRCONF(NETDEV_CHANGE): bond0: link becomes ready
> IPv6: ADDRCONF(NETDEV_UP): team0: link is not ready
> 8021q: adding VLAN 0 to HW filter on device team0
> usercopy: Kernel memory exposure attempt detected from SLAB object
> 'kmalloc-4096' (offset 2399, size 2626)!
> ------------[ cut here ]------------
> kernel BUG at mm/usercopy.c:100!
> invalid opcode: 0000 [#1] SMP KASAN
> CPU: 1 PID: 4718 Comm: syz-executor688 Not tainted 4.18.0-rc3-next-20180706+
> #1
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:usercopy_abort+0xbb/0xbd mm/usercopy.c:88
> Code: c0 e8 37 ec b8 ff ff 75 c8 48 8b 55 c0 4d 89 f9 ff 75 d0 4d 89 e8 48
> 89 d9 4c 89 e6 41 56 48 c7 c7 e0 4c f3 87 e8 37 a0 9f ff <0f> 0b e8 0c ec b8
> ff e8 97 42 f7 ff 4c 89 e1 8b 95 14 ff ff ff 31
> RSP: 0018:ffff8801d33a78b0 EFLAGS: 00010286
> RAX: 000000000000006b RBX: ffffffff88c10e70 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81634381 RDI: 0000000000000001
> RBP: ffff8801d33a7908 R08: ffff8801d1e2a200 R09: ffffed003b5e4fc0
> R10: ffffed003b5e4fc0 R11: ffff8801daf27e07 R12: ffffffff87f34bc0
> R13: ffffffff87f34a80 R14: ffffffff87f34a40 R15: ffffffff88c0c905
> FS:  00007f56a6072700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020001000 CR3: 00000001b8fdf000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  __check_heap_object+0xb5/0xb5 mm/slab.c:4445
>  check_heap_object mm/usercopy.c:236 [inline]
>  __check_object_size+0x4db/0x5f2 mm/usercopy.c:259
>  check_object_size include/linux/thread_info.h:119 [inline]
>  check_copy_size include/linux/thread_info.h:150 [inline]
>  copy_to_user include/linux/uaccess.h:154 [inline]
>  seq_read+0x578/0x10e0 fs/seq_file.c:211
>  do_loop_readv_writev fs/read_write.c:700 [inline]
>  do_iter_read+0x49e/0x650 fs/read_write.c:924
>  vfs_readv+0x175/0x1c0 fs/read_write.c:986
>  do_readv+0x11a/0x310 fs/read_write.c:1019
>  __do_sys_readv fs/read_write.c:1106 [inline]
>  __se_sys_readv fs/read_write.c:1103 [inline]
>  __x64_sys_readv+0x75/0xb0 fs/read_write.c:1103
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x446c09
> Code: e8 1c bc 02 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 5b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f56a6071d18 EFLAGS: 00000246 ORIG_RAX: 0000000000000013
> RAX: ffffffffffffffda RBX: 00000000006dcc5c RCX: 0000000000446c09
> RDX: 0000000000000002 RSI: 00000000200021c0 RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc58
> R13: 00007f56a6071d20 R14: 6f72746e6f632f2e R15: 0000000000000007
> Modules linked in:
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> ---[ end trace 532b9c3f493b2e4d ]---
> RIP: 0010:usercopy_abort+0xbb/0xbd mm/usercopy.c:88
> Code: c0 e8 37 ec b8 ff ff 75 c8 48 8b 55 c0 4d 89 f9 ff 75 d0 4d 89 e8 48
> 89 d9 4c 89 e6 41 56 48 c7 c7 e0 4c f3 87 e8 37 a0 9f ff <0f> 0b e8 0c ec b8
> ff e8 97 42 f7 ff 4c 89 e1 8b 95 14 ff ff ff 31
> RSP: 0018:ffff8801d33a78b0 EFLAGS: 00010286
> RAX: 000000000000006b RBX: ffffffff88c10e70 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81634381 RDI: 0000000000000001
> RBP: ffff8801d33a7908 R08: ffff8801d1e2a200 R09: ffffed003b5e4fc0
> R10: ffffed003b5e4fc0 R11: ffff8801daf27e07 R12: ffffffff87f34bc0
> R13: ffffffff87f34a80 R14: ffffffff87f34a40 R15: ffffffff88c0c905
> FS:  00007f56a6072700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020001000 CR3: 00000001b8fdf000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 

Fixed in -mm and linux-next by:

#syz fix: VFS: seq_file: ensure ->from is valid

- Eric