[syzbot] KFENCE: use-after-free in kvm_fastop_exception

syzbot
2021-08-16T08:27:29Z

Hello,

syzbot found the following issue on:

HEAD commit: b9011c7e671d Add linux-next specific files for 20210816
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15221f4e300000
kernel config: https://syzkaller.appspot.com/x/.config?x=a245d1aa4f055cc1
dashboard link: https://syzkaller.appspot.com/bug?extid=7b938780d5deeaaf938f
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7b938780d5deeaaf938f@syzkaller.appspotmail.com

==================================================================
BUG: KFENCE: use-after-free read in kvm_fastop_exception+0xf6a/0x1058

Use-after-free read at 0xffff88823bd2c020 (in kfence-#149):
kvm_fastop_exception+0xf6a/0x1058
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-#149: 0xffff88823bd2c000-0xffff88823bd2cfff, size=4096, cache=names_cache

allocated by task 22 on cpu 1 at 161.928971s:
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 on cpu 1 at 161.929182s:
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-rc5-next-20210816-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kvm_fastop_exception+0xf6a/0x1058
Code: d3 ed e9 f7 ae 6c f8 49 8d 0e 48 83 e1 f8 4c 8b 21 41 8d 0e 83 e1 07 c1 e1 03 49 d3 ec e9 4d bc 6c 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 3d c6 6c f8 bd
RSP: 0018:ffffc90000dcfae8 EFLAGS: 00010282
RAX: 34317974746d7367 RBX: ffff88806efb4330 RCX: ffff88823bd2c020
RDX: ffffed100ddf686d RSI: 0000000000000008 RDI: 0000000000000007
RBP: 0000000000000008 R08: 0000000000000000 R09: ffff88806efb4360
R10: ffffed100ddf686c R11: 0000000000000000 R12: ffff88823bd2c020
R13: ffff88823bd2c020 R14: ffff88806efb4360 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88823bd2c020 CR3: 000000004683b000 CR4: 00000000001506e0
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 f7 ae 6c f8 jmpq 0xf86caefe
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 4d bc 6c f8 jmpq 0xf86cbc6f
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 3d c6 6c f8 jmpq 0xf86cc67c
3f: bd .byte 0xbd

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