On 11/18/19 9:25 PM, Oliver Hartkopp wrote: > On 18/11/2019 20.05, syzbot wrote: >> Hello, >> >> syzbot found the following crash on: >> >> HEAD commit: 9c6a7162 kmsan: remove unneeded annotations in bio >> git tree: https://github.com/google/kmsan.git master >> console output: https://syzkaller.appspot.com/x/log.txt?x=14563416e00000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=9e324dfe9c7b0360 >> dashboard link: >> https://syzkaller.appspot.com/bug?extid=b02ff0707a97e4e79ebb >> compiler: clang version 9.0.0 (/home/glider/llvm/clang >> 80fee25776c2fb61e74c1ecb1a523375c2500b69) >> >> Unfortunately, I don't have any reproducer for this crash yet. >> >> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> Reported-by: syzbot+b02ff0707a97e4e79ebb@xxxxxxxxxxxxxxxxxxxxxxxxx >> >> ===================================================== >> BUG: KMSAN: uninit-value in can_receive+0x23c/0x5e0 net/can/af_can.c:649 >> CPU: 1 PID: 3490 Comm: syz-executor.2 Not tainted 5.4.0-rc5+ #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >> Google 01/01/2011 >> Call Trace: >> <IRQ> >> __dump_stack lib/dump_stack.c:77 [inline] >> dump_stack+0x191/0x1f0 lib/dump_stack.c:113 >> kmsan_report+0x128/0x220 mm/kmsan/kmsan_report.c:108 >> __msan_warning+0x73/0xe0 mm/kmsan/kmsan_instr.c:245 >> can_receive+0x23c/0x5e0 net/can/af_can.c:649 >> can_rcv+0x188/0x3a0 net/can/af_can.c:685 > > In line 649 of 5.4.0-rc5+ we can find a while() statement: > > while (!(can_skb_prv(skb)->skbcnt)) > can_skb_prv(skb)->skbcnt = atomic_inc_return(&skbcounter); > > In linux/include/linux/can/skb.h we see: > > static inline struct can_skb_priv *can_skb_prv(struct sk_buff *skb) > { > return (struct can_skb_priv *)(skb->head); > } > > IMO accessing can_skb_prv(skb)->skbcnt at this point is a valid > operation which has no uninitialized value. > > Can this probably be a false positive of KMSAN? The packet is injected via the packet socket into the kernel. Where does skb->head point to in this case? When the skb is a proper kernel-generated skb containing a CAN-2.0 or CAN-FD frame skb->head is maybe properly initialized? > do_softirq kernel/softirq.c:338 [inline] > __local_bh_enable_ip+0x184/0x1d0 kernel/softirq.c:190 > local_bh_enable+0x36/0x40 include/linux/bottom_half.h:32 > rcu_read_unlock_bh include/linux/rcupdate.h:688 [inline] > __dev_queue_xmit+0x38e8/0x4200 net/core/dev.c:3900 > dev_queue_xmit+0x4b/0x60 net/core/dev.c:3906 > packet_snd net/packet/af_packet.c:2959 [inline] > packet_sendmsg+0x82d7/0x92e0 net/packet/af_packet.c:2984 ^^^^^^^^^^^^^^^^^^^^^^ > sock_sendmsg_nosec net/socket.c:637 [inline] > sock_sendmsg net/socket.c:657 [inline] > ___sys_sendmsg+0x14ff/0x1590 net/socket.c:2311 > __sys_sendmsg net/socket.c:2356 [inline] > __do_sys_sendmsg net/socket.c:2365 [inline] > __se_sys_sendmsg+0x305/0x460 net/socket.c:2363 > __x64_sys_sendmsg+0x4a/0x70 net/socket.c:2363 > do_syscall_64+0xb6/0x160 arch/x86/entry/common.c:291 > entry_SYSCALL_64_after_hwframe+0x63/0xe7 Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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