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Date:   Thu, 6 Jun 2019 07:09:22 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     syzbot <syzbot+0341f6a4d729d4e0acf1@...kaller.appspotmail.com>,
        jmorris@...ei.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, serge@...lyn.com,
        syzkaller-bugs@...glegroups.com, takedakn@...data.co.jp,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: KASAN: use-after-free Read in tomoyo_realpath_from_path

Hello, Al.

syzbot found that SOCKET_I(d_backing_inode("struct path"->dentry))->sk
was already kfree()d when trying to calculate pathname for open().
"struct path"->dentry should remain valid but portion of memory
reachable via inode already became invalid. What should we do?

On 2019/06/06 3:42, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    788a0249 Merge tag 'arc-5.2-rc4' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=179848d4a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=60564cb52ab29d5b
> dashboard link: https://syzkaller.appspot.com/bug?extid=0341f6a4d729d4e0acf1
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13ac35baa00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+0341f6a4d729d4e0acf1@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in tomoyo_get_socket_name security/tomoyo/realpath.c:238 [inline]
> BUG: KASAN: use-after-free in tomoyo_realpath_from_path+0x722/0x7a0 security/tomoyo/realpath.c:284
> Read of size 2 at addr ffff8880a91276d0 by task syz-executor.3/17397
> 
> CPU: 0 PID: 17397 Comm: syz-executor.3 Not tainted 5.2.0-rc3+ #12
> 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.cold+0x7c/0x20d mm/kasan/report.c:188
>  __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
>  kasan_report+0x12/0x20 mm/kasan/common.c:614
>  __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:130
>  tomoyo_get_socket_name security/tomoyo/realpath.c:238 [inline]
>  tomoyo_realpath_from_path+0x722/0x7a0 security/tomoyo/realpath.c:284
>  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
>  tomoyo_check_open_permission+0x2a8/0x3f0 security/tomoyo/file.c:771
>  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:1454
>  do_dentry_open+0x373/0x1250 fs/open.c:765
>  vfs_open+0xa0/0xd0 fs/open.c:887
>  do_last fs/namei.c:3416 [inline]
>  path_openat+0x10e9/0x46d0 fs/namei.c:3533
>  do_filp_open+0x1a1/0x280 fs/namei.c:3563
>  do_sys_open+0x3fe/0x5d0 fs/open.c:1070
>  __do_sys_open fs/open.c:1088 [inline]
>  __se_sys_open fs/open.c:1083 [inline]
>  __x64_sys_open+0x7e/0xc0 fs/open.c:1083
>  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x413161
> Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00007f65230f8bb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
> RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000413161
> RDX: fffffffffffffffa RSI: 0000000000000000 RDI: 00007f65230f8bd0
> RBP: 000000000075c060 R08: 0000000000000050 R09: 000000000000000f
> R10: 0000000000000004 R11: 0000000000000293 R12: 00007f65230f96d4
> R13: 00000000004c83f6 R14: 00000000004dea40 R15: 00000000ffffffff
> 
> Allocated by task 17373:
>  save_stack+0x23/0x90 mm/kasan/common.c:71
>  set_track mm/kasan/common.c:79 [inline]
>  __kasan_kmalloc mm/kasan/common.c:489 [inline]
>  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
>  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
>  __do_kmalloc mm/slab.c:3660 [inline]
>  __kmalloc+0x15c/0x740 mm/slab.c:3669
>  kmalloc include/linux/slab.h:552 [inline]
>  sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1602
>  sk_alloc+0x39/0xf70 net/core/sock.c:1656
>  base_sock_create drivers/isdn/mISDN/socket.c:758 [inline]
>  mISDN_sock_create+0xb4/0x3a0 drivers/isdn/mISDN/socket.c:780
>  __sock_create+0x3d8/0x730 net/socket.c:1424
>  sock_create net/socket.c:1475 [inline]
>  __sys_socket+0x103/0x220 net/socket.c:1517
>  __do_sys_socket net/socket.c:1526 [inline]
>  __se_sys_socket net/socket.c:1524 [inline]
>  __x64_sys_socket+0x73/0xb0 net/socket.c:1524
>  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 17371:
>  save_stack+0x23/0x90 mm/kasan/common.c:71
>  set_track mm/kasan/common.c:79 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
>  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
>  __cache_free mm/slab.c:3432 [inline]
>  kfree+0xcf/0x220 mm/slab.c:3755
>  sk_prot_free net/core/sock.c:1639 [inline]
>  __sk_destruct+0x4f7/0x6e0 net/core/sock.c:1725
>  sk_destruct+0x7b/0x90 net/core/sock.c:1733
>  __sk_free+0xce/0x300 net/core/sock.c:1744
>  sk_free+0x42/0x50 net/core/sock.c:1755
>  sock_put include/net/sock.h:1723 [inline]
>  base_sock_release+0x269/0x279 drivers/isdn/mISDN/socket.c:628
>  __sock_release+0xce/0x2a0 net/socket.c:601
>  sock_close+0x1b/0x30 net/socket.c:1273
>  __fput+0x2ff/0x890 fs/file_table.c:280
>  ____fput+0x16/0x20 fs/file_table.c:313
>  task_work_run+0x145/0x1c0 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:185 [inline]
>  exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
>  prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
>  do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> The buggy address belongs to the object at ffff8880a91276c0
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 16 bytes inside of
>  2048-byte region [ffff8880a91276c0, ffff8880a9127ec0)
> The buggy address belongs to the page:
> page:ffffea0002a44980 refcount:1 mapcount:0 mapping:ffff8880aa400c40 index:0x0 compound_mapcount: 0
> flags: 0x1fffc0000010200(slab|head)
> raw: 01fffc0000010200 ffffea00022c9f88 ffffea0002234408 ffff8880aa400c40
> raw: 0000000000000000 ffff8880a91265c0 0000000100000003 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880a9127580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880a9127600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>> ffff8880a9127680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>                                                  ^
>  ffff8880a9127700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880a9127780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

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