linux-kernel - Re: [syzbot] KASAN: use-after-free Read in kernfs_add

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Date:   Sat, 22 Oct 2022 09:44:24 -0700
From:   syzbot <syzbot+ef17b5b364116518fd65@...kaller.appspotmail.com>
To:     hdanton@...a.com, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in kernfs_add_one

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
UBSAN: object-size-mismatch in wg_xmit

================================================================================
UBSAN: object-size-mismatch in ./include/linux/skbuff.h:2048:28
member access within address ffffc900000074c0 with insufficient space
for an object of type 'struct sk_buff'
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.15.0-rc5-syzkaller-00376-gcf52ad5ff16c-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
 ubsan_epilogue lib/ubsan.c:151 [inline]
 handle_object_size_mismatch lib/ubsan.c:232 [inline]
 ubsan_type_mismatch_common+0x1e6/0x390 lib/ubsan.c:245
 __ubsan_handle_type_mismatch_v1+0x4a/0x60 lib/ubsan.c:274
 __skb_queue_before include/linux/skbuff.h:2048 [inline]
 __skb_queue_tail include/linux/skbuff.h:2081 [inline]
 wg_xmit+0x565/0xda0 drivers/net/wireguard/device.c:182
 __netdev_start_xmit include/linux/netdevice.h:4988 [inline]
 netdev_start_xmit+0x7b/0x140 include/linux/netdevice.h:5002
 xmit_one net/core/dev.c:3576 [inline]
 dev_hard_start_xmit+0x182/0x2e0 net/core/dev.c:3592
 __dev_queue_xmit+0x1497/0x2140 net/core/dev.c:4202
 neigh_output include/net/neighbour.h:510 [inline]
 ip6_finish_output2+0xf45/0x1300 net/ipv6/ip6_output.c:126
 dst_output include/net/dst.h:450 [inline]
 NF_HOOK include/linux/netfilter.h:307 [inline]
 ndisc_send_skb+0x8c3/0xdd0 net/ipv6/ndisc.c:508
 addrconf_rs_timer+0x38c/0x5f0 net/ipv6/addrconf.c:3893
 call_timer_fn+0xf6/0x210 kernel/time/timer.c:1421
 expire_timers kernel/time/timer.c:1466 [inline]
 __run_timers+0x685/0x7e0 kernel/time/timer.c:1734
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1747
 __do_softirq+0x382/0x793 kernel/softirq.c:558
 __irq_exit_rcu+0xec/0x170 kernel/softirq.c:636
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:648
 sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1097
 </IRQ>
 asm_sysvec_apic_timer_interrupt+0x12/0x20
RIP: 0010:native_save_fl arch/x86/include/asm/irqflags.h:22 [inline]
RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:70 [inline]
RIP: 0010:arch_irqs_disabled arch/x86/include/asm/irqflags.h:132 [inline]
RIP: 0010:acpi_safe_halt+0xbc/0x160 drivers/acpi/processor_idle.c:110
Code: 83 e6 08 31 ff e8 24 39 89 f8 48 83 e3 08 75 73 4c 8d 64 24 20 e8 a4 1b 8f f8 eb 0c e8 4d 34 89 f8 0f 00 2d 16 3b c6 00 fb f4 <4c> 89 e3 48 c1 eb 03 42 80 3c 33 00 74 08 4c 89 e7 e8 9e c6 c8 f8
RSP: 0018:ffffffff8b407bc0 EFLAGS: 00000282
RAX: d4f825addbe56c00 RBX: 0000000000000000 RCX: ffffffff8f975703
RDX: ffffffff8b4bbf58 RSI: ffffffff894c55a0 RDI: ffffffff89a4bbe0
RBP: ffffffff8b407c40 R08: ffffffff81787bf0 R09: fffffbfff16976a9
R10: fffffbfff16976a9 R11: 1ffffffff16976a8 R12: ffffffff8b407be0
R13: ffff8880157d0064 R14: dffffc0000000000 R15: 1ffffffff1680f78
 acpi_idle_enter+0x371/0x520 drivers/acpi/processor_idle.c:688
 cpuidle_enter_state+0x2a8/0xaf0 drivers/cpuidle/cpuidle.c:237
 cpuidle_enter+0x59/0x90 drivers/cpuidle/cpuidle.c:351
 cpuidle_idle_call kernel/sched/idle.c:239 [inline]
 do_idle+0x389/0x590 kernel/sched/idle.c:306
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 start_kernel+0x4b9/0x568 init/main.c:1142
 secondary_startup_64_no_verify+0xb1/0xbb
================================================================================
----------------
Code disassembly (best guess):
   0:	83 e6 08             	and    $0x8,%esi
   3:	31 ff                	xor    %edi,%edi
   5:	e8 24 39 89 f8       	callq  0xf889392e
   a:	48 83 e3 08          	and    $0x8,%rbx
   e:	75 73                	jne    0x83
  10:	4c 8d 64 24 20       	lea    0x20(%rsp),%r12
  15:	e8 a4 1b 8f f8       	callq  0xf88f1bbe
  1a:	eb 0c                	jmp    0x28
  1c:	e8 4d 34 89 f8       	callq  0xf889346e
  21:	0f 00 2d 16 3b c6 00 	verw   0xc63b16(%rip)        # 0xc63b3e
  28:	fb                   	sti
  29:	f4                   	hlt
* 2a:	4c 89 e3             	mov    %r12,%rbx <-- trapping instruction
  2d:	48 c1 eb 03          	shr    $0x3,%rbx
  31:	42 80 3c 33 00       	cmpb   $0x0,(%rbx,%r14,1)
  36:	74 08                	je     0x40
  38:	4c 89 e7             	mov    %r12,%rdi
  3b:	e8 9e c6 c8 f8       	callq  0xf8c8c6de


Tested on:

commit:         cf52ad5f Merge tag 'driver-core-5.15-rc6' of git://git..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=10f1b16a880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e25c48e302d3bf01
dashboard link: https://syzkaller.appspot.com/bug?extid=ef17b5b364116518fd65
compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=14ca1022880000