linux-kernel - Re: Bug: use-after-free in udf

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Message-Id: <F20E928C-4150-4D9E-8E07-19CA0514E5EF@m.fudan.edu.cn>
Date: Thu, 2 Jan 2025 10:10:07 +0800
From: Kun Hu <huk23@...udan.edu.cn>
To: jack@...e.com
Cc: linux-kernel@...r.kernel.org,
 "jjtan24@...udan.edu.cn" <jjtan24@...udan.edu.cn>
Subject: Re: Bug: use-after-free in udf_statfs in fs/udf/super.c:2415


> 
> HEAD commit: dbfac60febfa806abb2d384cb6441e77335d2799
> git tree: upstream
> Console output: https://drive.google.com/file/d/1-YGytaKuh9M4hI6x27YjsE0vSyRFngf5/view?usp=sharing
> Kernel config: https://drive.google.com/file/d/1m1mk_YusR-tyusNHFuRbzdj8KUzhkeHC/view?usp=sharing
> C reproducer: /
> Syzlang reproducer: /
> 
> It seems that the issue originates from the udf_statfs function at line 2415, where 
> lvidiu might have been prematurely freed, leading to a Use-After-Free (UAF). 
> This could potentially pose some security risks. However, there is currently 
> no stable reproducer for this issue.
> It is also unclear whether this might have been caused by a race condition, potentially 
> involving premature freeing in another thread.
> 

Hi, we found this same issue again. I'm guessing it's necessary to put a lock around the if in the udf_sb_lvidiu function on line 115 in super.c aka udf_sb_lvidiu function to protect the pointer's lifecycle? A similar call stack would look like this:

BUG: unable to handle page fault for address: ffe21c001059f6e7
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 7fdd7067 P4D 7fdd6067 PUD 7fdd5067 PMD 0 
Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 3 UID: 0 PID: 10494 Comm: syz.7.1124 Not tainted 6.13.0-rc4 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:udf_statfs+0x61e/0x12c0 fs/udf/super.c:2415
Code: 4c 89 7b 20 4c 89 fd 4d 85 f6 0f 84 c0 00 00 00 e8 27 74 cd fe 49 8d 7e 20 48 b9 00 00 00 00 00 fc ff df 48 89 f8 48 c1 e8 03 <0f> b6 14 08 49 8d 46 23 48 89 c6 48 c1 ee 03 0f b6 0c 0e 48 89 fe
RSP: 0018:ffa0000003937c20 EFLAGS: 00010216
RAX: 1fe220001059f6e7 RBX: ffa0000003937e48 RCX: dffffc0000000000
RDX: ffa000000d347000 RSI: ff11000049e58000 RDI: ff11000082cfb738
RBP: 00000000f8b31fcb R08: 0000000000000001 R09: ff11000049e58a38
R10: fffffbfff2377aaa R11: ffffffff91bbd557 R12: 00000000f8b31fcb
R13: 0000000000000000 R14: ff11000082cfb718 R15: 00000000f8b31fcb
FS:  00007f6b73608700(0000) GS:ff1100006a380000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffe21c001059f6e7 CR3: 000000001dff8001 CR4: 0000000000771ef0
PKRU: 80000000
Call Trace:
 <TASK>
 statfs_by_dentry+0x138/0x220 fs/statfs.c:66
 vfs_statfs+0x44/0x2f0 fs/statfs.c:90
 fd_statfs+0x49/0x90 fs/statfs.c:121
 __do_sys_fstatfs+0x7a/0xf0 fs/statfs.c:214
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc3/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6b749b471d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6b73607ba8 EFLAGS: 00000246 ORIG_RAX: 000000000000008a
RAX: ffffffffffffffda RBX: 00007f6b74b76f80 RCX: 00007f6b749b471d
RDX: 0000000000000000 RSI: 0000000020000d40 RDI: 0000000000000005
RBP: 00007f6b74a29425 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6b74b76f8c R14: 00007f6b74b77018 R15: 00007f6b73607d40
 </TASK>
Modules linked in:
CR2: ffe21c001059f6e7
---[ end trace 0000000000000000 ]---
RIP: 0010:udf_statfs+0x61e/0x12c0 fs/udf/super.c:2415
Code: 4c 89 7b 20 4c 89 fd 4d 85 f6 0f 84 c0 00 00 00 e8 27 74 cd fe 49 8d 7e 20 48 b9 00 00 00 00 00 fc ff df 48 89 f8 48 c1 e8 03 <0f> b6 14 08 49 8d 46 23 48 89 c6 48 c1 ee 03 0f b6 0c 0e 48 89 fe
RSP: 0018:ffa0000003937c20 EFLAGS: 00010216
RAX: 1fe220001059f6e7 RBX: ffa0000003937e48 RCX: dffffc0000000000
RDX: ffa000000d347000 RSI: ff11000049e58000 RDI: ff11000082cfb738
RBP: 00000000f8b31fcb R08: 0000000000000001 R09: ff11000049e58a38
R10: fffffbfff2377aaa R11: ffffffff91bbd557 R12: 00000000f8b31fcb
R13: 0000000000000000 R14: ff11000082cfb718 R15: 00000000f8b31fcb
FS:  00007f6b73608700(0000) GS:ff1100006a380000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffe21c001059f6e7 CR3: 000000001dff8001 CR4: 0000000000771ef0
PKRU: 80000000
----------------
Code disassembly (best guess):
   0:	4c 89 7b 20          	mov    %r15,0x20(%rbx)
   4:	4c 89 fd             	mov    %r15,%rbp
   7:	4d 85 f6             	test   %r14,%r14
   a:	0f 84 c0 00 00 00    	je     0xd0
  10:	e8 27 74 cd fe       	callq  0xfecd743c
  15:	49 8d 7e 20          	lea    0x20(%r14),%rdi
  19:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  20:	fc ff df
  23:	48 89 f8             	mov    %rdi,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	0f b6 14 08          	movzbl (%rax,%rcx,1),%edx <-- trapping instruction
  2e:	49 8d 46 23          	lea    0x23(%r14),%rax
  32:	48 89 c6             	mov    %rax,%rsi
  35:	48 c1 ee 03          	shr    $0x3,%rsi
  39:	0f b6 0c 0e          	movzbl (%rsi,%rcx,1),%ecx
  3d:	48 89 fe             	mov    %rdi,%rsi

——
Thanks,
Kun Hu