Subject: [syzbot] bpf-next test error: KFENCE: use-after-free in kvm_fastop_exception

From: syzbot <[email-masked]>
Date: Thu, 09 Sep 2021 17:34:32 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    27151f177827 Merge tag 'perf-tools-for-v5.15-2021-09-04' o..
git tree:       bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=112e0b15300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ac2f9cc43f6b17e4
dashboard link: https://syzkaller.appspot.com/bug?extid=19d0d18201298c185c4f
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

==================================================================
BUG: KFENCE: use-after-free read in kvm_fastop_exception+0xf6d/0x105b

Use-after-free read at 0xffff88823bd7c020 (in kfence-#189):
 kvm_fastop_exception+0xf6d/0x105b
 d_lookup+0xd8/0x170 fs/dcache.c:2370
 lookup_dcache+0x1e/0x130 fs/namei.c:1520
 __lookup_hash+0x29/0x180 fs/namei.c:1543
 kern_path_locked+0x17e/0x320 fs/namei.c:2567
 handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312
 handle drivers/base/devtmpfs.c:382 [inline]
 devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline]
 devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

kfence-#189 [0xffff88823bd7c000-0xffff88823bd7cfff, size=4096, cache=names_cache] allocated by task 22:
 getname_kernel+0x4e/0x370 fs/namei.c:226
 kern_path_locked+0x71/0x320 fs/namei.c:2558
 handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312
 handle drivers/base/devtmpfs.c:382 [inline]
 devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline]
 devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

freed by task 22:
 putname.part.0+0xe1/0x120 fs/namei.c:270
 putname include/linux/err.h:41 [inline]
 filename_parentat fs/namei.c:2547 [inline]
 kern_path_locked+0xc2/0x320 fs/namei.c:2558
 handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312
 handle drivers/base/devtmpfs.c:382 [inline]
 devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline]
 devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

CPU: 1 PID: 22 Comm: kdevtmpfs Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kvm_fastop_exception+0xf6d/0x105b
Code: d3 ed e9 54 03 6f f8 49 8d 0e 48 83 e1 f8 4c 8b 21 41 8d 0e 83 e1 07 c1 e1 03 49 d3 ec e9 aa 10 6f f8 49 8d 4d 00 48 83 e1 f8 <4c> 8b 21 41 8d 4d 00 83 e1 07 c1 e1 03 49 d3 ec e9 9a 1a 6f f8 bd
RSP: 0018:ffffc90000dcfae8 EFLAGS: 00010282
RAX: 0000003461736376 RBX: ffff88806f6feef0 RCX: ffff88823bd7c020
RDX: ffffed100dedfde5 RSI: 0000000000000005 RDI: 0000000000000007
RBP: 0000000000000005 R08: 0000000000000000 R09: ffff88806f6fef20
R10: ffffed100dedfde4 R11: 0000000000000000 R12: ffff88823bd7c020
R13: ffff88823bd7c020 R14: ffff88806f6fef20 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88823bd7c020 CR3: 00000000723c1000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 d_lookup+0xd8/0x170 fs/dcache.c:2370
 lookup_dcache+0x1e/0x130 fs/namei.c:1520
 __lookup_hash+0x29/0x180 fs/namei.c:1543
 kern_path_locked+0x17e/0x320 fs/namei.c:2567
 handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312
 handle drivers/base/devtmpfs.c:382 [inline]
 devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline]
 devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
==================================================================
----------------
Code disassembly (best guess):
   0:	d3 ed                	shr    %cl,%ebp
   2:	e9 54 03 6f f8       	jmpq   0xf86f035b
   7:	49 8d 0e             	lea    (%r14),%rcx
   a:	48 83 e1 f8          	and    $0xfffffffffffffff8,%rcx
   e:	4c 8b 21             	mov    (%rcx),%r12
  11:	41 8d 0e             	lea    (%r14),%ecx
  14:	83 e1 07             	and    $0x7,%ecx
  17:	c1 e1 03             	shl    $0x3,%ecx
  1a:	49 d3 ec             	shr    %cl,%r12
  1d:	e9 aa 10 6f f8       	jmpq   0xf86f10cc
  22:	49 8d 4d 00          	lea    0x0(%r13),%rcx
  26:	48 83 e1 f8          	and    $0xfffffffffffffff8,%rcx
* 2a:	4c 8b 21             	mov    (%rcx),%r12 <-- trapping instruction
  2d:	41 8d 4d 00          	lea    0x0(%r13),%ecx
  31:	83 e1 07             	and    $0x7,%ecx
  34:	c1 e1 03             	shl    $0x3,%ecx
  37:	49 d3 ec             	shr    %cl,%r12
  3a:	e9 9a 1a 6f f8       	jmpq   0xf86f1ad9
  3f:	bd                   	.byte 0xbd

---
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