Subject: Re: [syzbot] KMSAN: uninit-value in can_send

From: Oleksij Rempel <[email-masked]>
Date: Fri, 4 Nov 2022 06:22:35 +0100

Hi Oliver,

On Thu, Nov 03, 2022 at 10:21:15PM +0100, Oliver Hartkopp wrote:
> Good catch!
> 
> That's a correct issue caused by only filling the CAN frame header with
> can_id and len in j1939_send_one():
> 
> https://elixir.bootlin.com/linux/v6.0.6/source/net/can/j1939/main.c#L345
> 
> @Oleksij: Can you please (zero)initialize the unused elements in struct
> can_frame (namely __pad, __res0, len8_dlc) in j1939_send_one()?
> 
> Or do you want me to create a patch for it?

I'll not be able to make it today. I'll be glad if you could do it 

Thanks and best regards,
Oleksij

> 
> On 03.11.22 17:22, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    4a3e741a3d6a x86: fortify: kmsan: fix KMSAN fortify builds
> > git tree:       https://github.com/google/kmsan.git master
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=14247636880000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=c19210a0c25eebb
> > dashboard link: https://syzkaller.appspot.com/bug?extid=d168ec0caca4697e03b1
> > compiler:       clang version 15.0.0 (https://github.com/llvm/llvm-project.git 610139d2d9ce6746b3c617fb3e2f7886272d26ff), GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13e16e86880000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1535a2f6880000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/fbb1997bc1e0/disk-4a3e741a.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/d5dd2e1efaa4/vmlinux-4a3e741a.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: [email-masked]
> > 
> > =====================================================
> > BUG: KMSAN: uninit-value in can_is_canxl_skb include/linux/can/skb.h:128 [inline]
> > BUG: KMSAN: uninit-value in can_send+0x269/0x1100 net/can/af_can.c:205
> >   can_is_canxl_skb include/linux/can/skb.h:128 [inline]
> >   can_send+0x269/0x1100 net/can/af_can.c:205
> >   j1939_send_one+0x40f/0x4d0 net/can/j1939/main.c:352
> >   j1939_xtp_do_tx_ctl+0x69f/0x9e0 net/can/j1939/transport.c:664
> >   j1939_tp_tx_ctl net/can/j1939/transport.c:672 [inline]
> >   j1939_session_tx_rts net/can/j1939/transport.c:740 [inline]
> >   j1939_xtp_txnext_transmiter net/can/j1939/transport.c:880 [inline]
> >   j1939_tp_txtimer+0x35bb/0x4520 net/can/j1939/transport.c:1158
> >   __run_hrtimer+0x298/0x910 kernel/time/hrtimer.c:1685
> >   __hrtimer_run_queues kernel/time/hrtimer.c:1749 [inline]
> >   hrtimer_run_softirq+0x4b0/0x870 kernel/time/hrtimer.c:1766
> >   __do_softirq+0x1c5/0x7b9 kernel/softirq.c:571
> >   invoke_softirq+0x8f/0x100 kernel/softirq.c:445
> >   __irq_exit_rcu+0x5a/0x110 kernel/softirq.c:650
> >   irq_exit_rcu+0xe/0x10 kernel/softirq.c:662
> >   sysvec_apic_timer_interrupt+0x9a/0xc0 arch/x86/kernel/apic/apic.c:1107
> >   asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:649
> >   __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
> >   _raw_spin_unlock_irqrestore+0x2f/0x50 kernel/locking/spinlock.c:194
> >   unlock_hrtimer_base kernel/time/hrtimer.c:1017 [inline]
> >   hrtimer_start_range_ns+0xaba/0xb50 kernel/time/hrtimer.c:1301
> >   hrtimer_start include/linux/hrtimer.h:418 [inline]
> >   j1939_tp_schedule_txtimer+0xbe/0x100 net/can/j1939/transport.c:697
> >   j1939_sk_send_loop net/can/j1939/socket.c:1143 [inline]
> >   j1939_sk_sendmsg+0x1c2c/0x25d0 net/can/j1939/socket.c:1256
> >   sock_sendmsg_nosec net/socket.c:714 [inline]
> >   sock_sendmsg net/socket.c:734 [inline]
> >   ____sys_sendmsg+0xa8e/0xe70 net/socket.c:2482
> >   ___sys_sendmsg+0x2a1/0x3f0 net/socket.c:2536
> >   __sys_sendmsg net/socket.c:2565 [inline]
> >   __do_sys_sendmsg net/socket.c:2574 [inline]
> >   __se_sys_sendmsg net/socket.c:2572 [inline]
> >   __x64_sys_sendmsg+0x367/0x540 net/socket.c:2572
> >   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >   do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > 
> > Uninit was created at:
> >   slab_post_alloc_hook mm/slab.h:742 [inline]
> >   slab_alloc_node mm/slub.c:3398 [inline]
> >   __kmem_cache_alloc_node+0x6ee/0xc90 mm/slub.c:3437
> >   __do_kmalloc_node mm/slab_common.c:954 [inline]
> >   __kmalloc_node_track_caller+0x117/0x3d0 mm/slab_common.c:975
> >   kmalloc_reserve net/core/skbuff.c:437 [inline]
> >   __alloc_skb+0x34a/0xca0 net/core/skbuff.c:509
> >   alloc_skb include/linux/skbuff.h:1267 [inline]
> >   j1939_tp_tx_dat_new net/can/j1939/transport.c:593 [inline]
> >   j1939_xtp_do_tx_ctl+0xa3/0x9e0 net/can/j1939/transport.c:654
> >   j1939_tp_tx_ctl net/can/j1939/transport.c:672 [inline]
> >   j1939_session_tx_rts net/can/j1939/transport.c:740 [inline]
> >   j1939_xtp_txnext_transmiter net/can/j1939/transport.c:880 [inline]
> >   j1939_tp_txtimer+0x35bb/0x4520 net/can/j1939/transport.c:1158
> >   __run_hrtimer+0x298/0x910 kernel/time/hrtimer.c:1685
> >   __hrtimer_run_queues kernel/time/hrtimer.c:1749 [inline]
> >   hrtimer_run_softirq+0x4b0/0x870 kernel/time/hrtimer.c:1766
> >   __do_softirq+0x1c5/0x7b9 kernel/softirq.c:571
> > 
> > CPU: 0 PID: 3506 Comm: syz-executor289 Not tainted 6.1.0-rc2-syzkaller-61955-g4a3e741a3d6a #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
> > =====================================================
> > 
> > 
> > ---
> > 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 [email-masked].
> > 
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > syzbot can test patches for this issue, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> 

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