syzbot <syzbot+0631d878823ce2411636@xxxxxxxxxxxxxxxxxxxxxxxxx> writes: > syzbot found the following crash on: > > HEAD commit: 96c6c319 net: kasan: kmsan: support CONFIG_GENERIC_CSUM on.. > git tree: https://github.com/google/kmsan.git master > console output: https://syzkaller.appspot.com/x/log.txt?x=11f103bce00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=9e324dfe9c7b0360 > dashboard link: https://syzkaller.appspot.com/bug?extid=0631d878823ce2411636 > compiler: clang version 9.0.0 (/home/glider/llvm/clang > 80fee25776c2fb61e74c1ecb1a523375c2500b69) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10dd9774e00000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13651a24e00000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+0631d878823ce2411636@xxxxxxxxxxxxxxxxxxxxxxxxx > > ===================================================== > BUG: KMSAN: uninit-value in cdc_ncm_set_dgram_size+0x6ba/0xbc0 > drivers/net/usb/cdc_ncm.c:587 > CPU: 0 PID: 11865 Comm: kworker/0:3 Not tainted 5.4.0-rc5+ #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, > BIOS Google 01/01/2011 > Workqueue: usb_hub_wq hub_event > Call Trace: > __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 > cdc_ncm_set_dgram_size+0x6ba/0xbc0 drivers/net/usb/cdc_ncm.c:587 .. > Variable was created at: > cdc_ncm_set_dgram_size+0xf5/0xbc0 drivers/net/usb/cdc_ncm.c:564 > cdc_ncm_set_dgram_size+0xf5/0xbc0 drivers/net/usb/cdc_ncm.c:564 > ===================================================== This looks like a false positive to me. max_datagram_size is two bytes declared as __le16 max_datagram_size; and the code leading up to the access on drivers/net/usb/cdc_ncm.c:587 is: /* read current mtu value from device */ err = usbnet_read_cmd(dev, USB_CDC_GET_MAX_DATAGRAM_SIZE, USB_TYPE_CLASS | USB_DIR_IN | USB_RECIP_INTERFACE, 0, iface_no, &max_datagram_size, 2); if (err < 0) { dev_dbg(&dev->intf->dev, "GET_MAX_DATAGRAM_SIZE failed\n"); goto out; } if (le16_to_cpu(max_datagram_size) == ctx->max_datagram_size) AFAICS, there is no way max_datagram_size can be uninitialized here. usbnet_read_cmd() either read 2 bytes into it or returned an error, causing the access to be skipped. Or am I missing something? I tried to read the syzbot manual to figure out how to tell this to the bot, but couldn't find that either. Not my day today it seems ;-) Please let me know what to do about this. Bjørn
