Re: KASAN: use-after-free Read in ceph_destroy_options

[Ilya Dryomov <idryomov@gmail.com>]

On Thu, Aug 23, 2018 at 4:35 PM syzbot
<syzbot+8ab6f1042021b4eed062@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    cc3d190b12b3 Add linux-next specific files for 20180822
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=107d322e400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ce7f661707bc9904
> dashboard link: https://syzkaller.appspot.com/bug?extid=8ab6f1042021b4eed062
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+8ab6f1042021b4eed062@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in ceph_destroy_options+0xe0/0x110
> net/ceph/ceph_common.c:289
> Read of size 8 at addr ffff8801d8f4dd50 by task syz-executor2/7977
>
> CPU: 0 PID: 7977 Comm: syz-executor2 Not tainted 4.18.0-next-20180822+ #45
> 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+0x1c9/0x2b4 lib/dump_stack.c:113
>   print_address_description+0x6c/0x20b mm/kasan/report.c:256
>   kasan_report_error mm/kasan/report.c:354 [inline]
>   kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
>   __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>   ceph_destroy_options+0xe0/0x110 net/ceph/ceph_common.c:289
>   ceph_mount+0xeab/0x1cc0 fs/ceph/super.c:1047
>   legacy_get_tree+0x131/0x460 fs/fs_context.c:732
>   vfs_get_tree+0x1cb/0x5c0 fs/super.c:1746
>   do_new_mount fs/namespace.c:2627 [inline]
>   do_mount+0x6f9/0x1e30 fs/namespace.c:2951
>   ksys_mount+0x12d/0x140 fs/namespace.c:3167
>   __do_sys_mount fs/namespace.c:3181 [inline]
>   __se_sys_mount fs/namespace.c:3178 [inline]
>   __x64_sys_mount+0xbe/0x150 fs/namespace.c:3178
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457089
> Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fae7dd45c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007fae7dd466d4 RCX: 0000000000457089
> RDX: 0000000020000080 RSI: 0000000020000040 RDI: 0000000020000000
> RBP: 00000000009300a0 R08: 00000000200000c0 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000004d2750 R14: 00000000004c7bdf R15: 0000000000000000
>
> Allocated by task 7977:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>   set_track mm/kasan/kasan.c:460 [inline]
>   kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>   kmem_cache_alloc_trace+0x152/0x730 mm/slab.c:3620
>   kmalloc include/linux/slab.h:513 [inline]
>   kzalloc include/linux/slab.h:707 [inline]
>   ceph_parse_options+0xfe/0x1230 net/ceph/ceph_common.c:355
>   parse_mount_options fs/ceph/super.c:491 [inline]
>   ceph_mount+0x4b9/0x1cc0 fs/ceph/super.c:1036
>   legacy_get_tree+0x131/0x460 fs/fs_context.c:732
>   vfs_get_tree+0x1cb/0x5c0 fs/super.c:1746
>   do_new_mount fs/namespace.c:2627 [inline]
>   do_mount+0x6f9/0x1e30 fs/namespace.c:2951
>   ksys_mount+0x12d/0x140 fs/namespace.c:3167
>   __do_sys_mount fs/namespace.c:3181 [inline]
>   __se_sys_mount fs/namespace.c:3178 [inline]
>   __x64_sys_mount+0xbe/0x150 fs/namespace.c:3178
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 7977:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>   set_track mm/kasan/kasan.c:460 [inline]
>   __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>   kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>   __cache_free mm/slab.c:3498 [inline]
>   kfree+0xd9/0x210 mm/slab.c:3813
>   ceph_destroy_options+0xd4/0x110 net/ceph/ceph_common.c:295
>   ceph_destroy_client+0x139/0x1a0 net/ceph/ceph_common.c:680
>   create_fs_client fs/ceph/super.c:677 [inline]
>   ceph_mount+0xf6e/0x1cc0 fs/ceph/super.c:1043
>   legacy_get_tree+0x131/0x460 fs/fs_context.c:732
>   vfs_get_tree+0x1cb/0x5c0 fs/super.c:1746
>   do_new_mount fs/namespace.c:2627 [inline]
>   do_mount+0x6f9/0x1e30 fs/namespace.c:2951
>   ksys_mount+0x12d/0x140 fs/namespace.c:3167
>   __do_sys_mount fs/namespace.c:3181 [inline]
>   __se_sys_mount fs/namespace.c:3178 [inline]
>   __x64_sys_mount+0xbe/0x150 fs/namespace.c:3178
>   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8801d8f4dc80
>   which belongs to the cache kmalloc-256 of size 256
> The buggy address is located 208 bytes inside of
>   256-byte region [ffff8801d8f4dc80, ffff8801d8f4dd80)
> The buggy address belongs to the page:
> page:ffffea000763d340 count:1 mapcount:0 mapping:ffff8801dac007c0 index:0x0
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea0006c0e448 ffffea00072ca688 ffff8801dac007c0
> raw: 0000000000000000 ffff8801d8f4d000 000000010000000c 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>   ffff8801d8f4dc00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>   ffff8801d8f4dc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8801d8f4dd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                   ^
>   ffff8801d8f4dd80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>   ffff8801d8f4de00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

Thanks for the report, I'll prepare a patch.

                Ilya