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Date:   Wed, 5 Jul 2023 15:05:56 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     syzbot <syzbot+a67fc5321ffb4b311c98@syzkaller.appspotmail.com>,
        Jeff Layton <jlayton@kernel.org>, amir73il@gmail.com
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-unionfs@vger.kernel.org, miklos@szeredi.hu,
        syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [overlayfs?] general protection fault in d_path
Message-ID: <20230705-aufgearbeitet-kaffee-44ff4731a7dd@brauner>
References: <0000000000004f34d705ffbc2604@google.com>
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On Wed, Jul 05, 2023 at 05:00:45AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    d528014517f2 Revert ".gitignore: ignore *.cover and *.mbx"
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14fad002a80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1085b4238c9eb6ba
> dashboard link: https://syzkaller.appspot.com/bug?extid=a67fc5321ffb4b311c98
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/fef94e788067/disk-d5280145.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/576412ea518b/vmlinux-d5280145.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/685a0e4be06b/bzImage-d5280145.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a67fc5321ffb4b311c98@syzkaller.appspotmail.com
> 
> general protection fault, probably for non-canonical address 0xdffffc000000000a: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
> CPU: 1 PID: 10127 Comm: syz-executor.3 Not tainted 6.4.0-syzkaller-11478-gd528014517f2 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
> RIP: 0010:__lock_acquire+0x10d/0x7f70 kernel/locking/lockdep.c:5012
> Code: 85 75 18 00 00 83 3d 15 c8 2c 0d 00 48 89 9c 24 10 01 00 00 0f 84 f8 0f 00 00 83 3d 5c de b3 0b 00 74 34 48 89 d0 48 c1 e8 03 <42> 80 3c 00 00 74 1a 48 89 d7 e8 b4 51 79 00 48 8b 94 24 80 00 00
> RSP: 0018:ffffc900169be9e0 EFLAGS: 00010006
> RAX: 000000000000000a RBX: 1ffff92002d37d60 RCX: 0000000000000002
> RDX: 0000000000000050 RSI: 0000000000000000 RDI: 0000000000000050
> RBP: ffffc900169beca8 R08: dffffc0000000000 R09: 0000000000000001
> R10: dffffc0000000000 R11: fffffbfff1d2fe76 R12: 0000000000000000
> R13: 0000000000000001 R14: 0000000000000002 R15: ffff88802091d940
> FS:  0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa22a3fe000 CR3: 000000004b5e1000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  lock_acquire+0x1e3/0x520 kernel/locking/lockdep.c:5761
>  seqcount_lockdep_reader_access+0x139/0x220 include/linux/seqlock.h:102
>  get_fs_root_rcu fs/d_path.c:244 [inline]
>  d_path+0x2f0/0x6e0 fs/d_path.c:286
>  audit_log_d_path+0xd3/0x310 kernel/audit.c:2139
>  dump_common_audit_data security/lsm_audit.c:224 [inline]
>  common_lsm_audit+0x7cf/0x1a90 security/lsm_audit.c:458
>  smack_log+0x421/0x540 security/smack/smack_access.c:383
>  smk_tskacc+0x2ff/0x360 security/smack/smack_access.c:253
>  smack_inode_getattr+0x203/0x270 security/smack/smack_lsm.c:1202
>  security_inode_getattr+0xd3/0x120 security/security.c:2114
>  vfs_getattr+0x25/0x70 fs/stat.c:167
>  ovl_getattr+0x1b1/0xf70 fs/overlayfs/inode.c:174
>  ima_check_last_writer security/integrity/ima/ima_main.c:171 [inline]
>  ima_file_free+0x26e/0x4b0 security/integrity/ima/ima_main.c:203

Ugh, I think the root of this might all be the call back into
vfs_getattr() that happens on overlayfs:

__fput()
-> ima_file_free()
   -> mutex_lock()
   -> vfs_getattr_nosec()
      -> i_op->getattr() == ovl_getattr()
         -> vfs_getattr()
	    -> security_inode_getattr()
   -> mutex_unlock()

So either overlayfs needs to call vfs_getattr_nosec() when the request
comes from vfs_getattr_nosec() or this needs to use
backing_file_real_path() to operate on the real underlying path.

Thoughts?

>  __fput+0x36a/0x950 fs/file_table.c:378
>  task_work_run+0x24a/0x300 kernel/task_work.c:179
>  exit_task_work include/linux/task_work.h:38 [inline]
>  do_exit+0x68f/0x2290 kernel/exit.c:874
>  do_group_exit+0x206/0x2c0 kernel/exit.c:1024
>  get_signal+0x1709/0x17e0 kernel/signal.c:2877
>  arch_do_signal_or_restart+0x91/0x670 arch/x86/kernel/signal.c:308
>  exit_to_user_mode_loop+0x6a/0x100 kernel/entry/common.c:168
>  exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:204
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:286 [inline]
>  syscall_exit_to_user_mode+0x64/0x280 kernel/entry/common.c:297
>  do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f7f3ca8c389
> Code: Unable to access opcode bytes at 0x7f7f3ca8c35f.
> RSP: 002b:00007f7f3d741168 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
> RAX: fffffffffffffffb RBX: 00007f7f3cbac050 RCX: 00007f7f3ca8c389
> RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000020000180
> RBP: 00007f7f3cad7493 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fff8432555f R14: 00007f7f3d741300 R15: 0000000000022000
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:__lock_acquire+0x10d/0x7f70 kernel/locking/lockdep.c:5012
> Code: 85 75 18 00 00 83 3d 15 c8 2c 0d 00 48 89 9c 24 10 01 00 00 0f 84 f8 0f 00 00 83 3d 5c de b3 0b 00 74 34 48 89 d0 48 c1 e8 03 <42> 80 3c 00 00 74 1a 48 89 d7 e8 b4 51 79 00 48 8b 94 24 80 00 00
> RSP: 0018:ffffc900169be9e0 EFLAGS: 00010006
> RAX: 000000000000000a RBX: 1ffff92002d37d60 RCX: 0000000000000002
> RDX: 0000000000000050 RSI: 0000000000000000 RDI: 0000000000000050
> RBP: ffffc900169beca8 R08: dffffc0000000000 R09: 0000000000000001
> R10: dffffc0000000000 R11: fffffbfff1d2fe76 R12: 0000000000000000
> R13: 0000000000000001 R14: 0000000000000002 R15: ffff88802091d940
> FS:  0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa22a3fe000 CR3: 000000004b5e1000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> ----------------
> Code disassembly (best guess):
>    0:	85 75 18             	test   %esi,0x18(%rbp)
>    3:	00 00                	add    %al,(%rax)
>    5:	83 3d 15 c8 2c 0d 00 	cmpl   $0x0,0xd2cc815(%rip)        # 0xd2cc821
>    c:	48 89 9c 24 10 01 00 	mov    %rbx,0x110(%rsp)
>   13:	00
>   14:	0f 84 f8 0f 00 00    	je     0x1012
>   1a:	83 3d 5c de b3 0b 00 	cmpl   $0x0,0xbb3de5c(%rip)        # 0xbb3de7d
>   21:	74 34                	je     0x57
>   23:	48 89 d0             	mov    %rdx,%rax
>   26:	48 c1 e8 03          	shr    $0x3,%rax
> * 2a:	42 80 3c 00 00       	cmpb   $0x0,(%rax,%r8,1) <-- trapping instruction
>   2f:	74 1a                	je     0x4b
>   31:	48 89 d7             	mov    %rdx,%rdi
>   34:	e8 b4 51 79 00       	callq  0x7951ed
>   39:	48                   	rex.W
>   3a:	8b                   	.byte 0x8b
>   3b:	94                   	xchg   %eax,%esp
>   3c:	24 80                	and    $0x80,%al
> 
> 
> ---
> This report 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@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the bug is already fixed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want to change bug's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the bug is a duplicate of another bug, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup