On Fri, Aug 09, 2019 at 12:51:00PM -0400, Alan Stern wrote: > Greg: > > See below... > > On Fri, 9 Aug 2019, syzbot wrote: > > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: e96407b4 usb-fuzzer: main usb gadget fuzzer driver > > git tree: https://github.com/google/kasan.git usb-fuzzer > > console output: https://syzkaller.appspot.com/x/log.txt?x=15a16f26600000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e > > dashboard link: https://syzkaller.appspot.com/bug?extid=30cf45ebfe0b0c4847a1 > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1416df26600000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11ce511c600000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+30cf45ebfe0b0c4847a1@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ================================================================== > > BUG: KASAN: use-after-free in __mutex_lock_common > > kernel/locking/mutex.c:912 [inline] > > BUG: KASAN: use-after-free in __mutex_lock+0xf23/0x1360 > > kernel/locking/mutex.c:1077 > > Read of size 8 at addr ffff8881d21fc2d8 by task syz-executor834/1878 > > > > CPU: 0 PID: 1878 Comm: syz-executor834 Not tainted 5.3.0-rc2+ #25 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > Google 01/01/2011 > > Call Trace: > > __dump_stack lib/dump_stack.c:77 [inline] > > dump_stack+0xca/0x13e lib/dump_stack.c:113 > > print_address_description+0x6a/0x32c mm/kasan/report.c:351 > > __kasan_report.cold+0x1a/0x33 mm/kasan/report.c:482 > > kasan_report+0xe/0x12 mm/kasan/common.c:612 > > __mutex_lock_common kernel/locking/mutex.c:912 [inline] > > __mutex_lock+0xf23/0x1360 kernel/locking/mutex.c:1077 > > ld_usb_release+0xb1/0x400 drivers/usb/misc/ldusb.c:386 > > __fput+0x2d7/0x840 fs/file_table.c:280 > > task_work_run+0x13f/0x1c0 kernel/task_work.c:113 > > tracehook_notify_resume include/linux/tracehook.h:188 [inline] > > exit_to_usermode_loop+0x1d2/0x200 arch/x86/entry/common.c:163 > > prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline] > > syscall_return_slowpath arch/x86/entry/common.c:274 [inline] > > do_syscall_64+0x45f/0x580 arch/x86/entry/common.c:299 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > RIP: 0033:0x406b31 > > Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 > > 83 ec 08 e8 6a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 > > 89 c2 e8 b3 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01 > > RSP: 002b:00007ffcf13bd080 EFLAGS: 00000293 ORIG_RAX: 0000000000000003 > > RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000406b31 > > RDX: fffffffffffffff7 RSI: 0000000000000080 RDI: 0000000000000004 > > RBP: 0000000000000159 R08: 0000000000000020 R09: 0000000000000020 > > R10: 00007ffcf13bd0b0 R11: 0000000000000293 R12: 000000000001d884 > > R13: 0000000000000004 R14: 00000000006e39ec R15: 0000000000000064 > > > > Allocated by task 1775: > > save_stack+0x1b/0x80 mm/kasan/common.c:69 > > set_track mm/kasan/common.c:77 [inline] > > __kasan_kmalloc mm/kasan/common.c:487 [inline] > > __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:460 > > kmalloc include/linux/slab.h:552 [inline] > > kzalloc include/linux/slab.h:748 [inline] > > ld_usb_probe+0x6e/0xa65 drivers/usb/misc/ldusb.c:661 > > usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361 > > really_probe+0x281/0x650 drivers/base/dd.c:548 > > driver_probe_device+0x101/0x1b0 drivers/base/dd.c:709 > > __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:816 > > bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454 > > __device_attach+0x217/0x360 drivers/base/dd.c:882 > > bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514 > > device_add+0xae6/0x16f0 drivers/base/core.c:2114 > > usb_set_configuration+0xdf6/0x1670 drivers/usb/core/message.c:2023 > > generic_probe+0x9d/0xd5 drivers/usb/core/generic.c:210 > > usb_probe_device+0x99/0x100 drivers/usb/core/driver.c:266 > > really_probe+0x281/0x650 drivers/base/dd.c:548 > > driver_probe_device+0x101/0x1b0 drivers/base/dd.c:709 > > __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:816 > > bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454 > > __device_attach+0x217/0x360 drivers/base/dd.c:882 > > bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514 > > device_add+0xae6/0x16f0 drivers/base/core.c:2114 > > usb_new_device.cold+0x6a4/0xe79 drivers/usb/core/hub.c:2536 > > hub_port_connect drivers/usb/core/hub.c:5098 [inline] > > hub_port_connect_change drivers/usb/core/hub.c:5213 [inline] > > port_event drivers/usb/core/hub.c:5359 [inline] > > hub_event+0x1b5c/0x3640 drivers/usb/core/hub.c:5441 > > process_one_work+0x92b/0x1530 kernel/workqueue.c:2269 > > worker_thread+0x96/0xe20 kernel/workqueue.c:2415 > > kthread+0x318/0x420 kernel/kthread.c:255 > > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 > > > > Freed by task 1775: > > save_stack+0x1b/0x80 mm/kasan/common.c:69 > > set_track mm/kasan/common.c:77 [inline] > > __kasan_slab_free+0x130/0x180 mm/kasan/common.c:449 > > slab_free_hook mm/slub.c:1423 [inline] > > slab_free_freelist_hook mm/slub.c:1470 [inline] > > slab_free mm/slub.c:3012 [inline] > > kfree+0xe4/0x2f0 mm/slub.c:3953 > > ld_usb_probe+0x728/0xa65 drivers/usb/misc/ldusb.c:744 > > usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361 > > really_probe+0x281/0x650 drivers/base/dd.c:548 > > driver_probe_device+0x101/0x1b0 drivers/base/dd.c:709 > > __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:816 > > bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454 > > __device_attach+0x217/0x360 drivers/base/dd.c:882 > > bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514 > > device_add+0xae6/0x16f0 drivers/base/core.c:2114 > > usb_set_configuration+0xdf6/0x1670 drivers/usb/core/message.c:2023 > > generic_probe+0x9d/0xd5 drivers/usb/core/generic.c:210 > > usb_probe_device+0x99/0x100 drivers/usb/core/driver.c:266 > > really_probe+0x281/0x650 drivers/base/dd.c:548 > > driver_probe_device+0x101/0x1b0 drivers/base/dd.c:709 > > __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:816 > > bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454 > > __device_attach+0x217/0x360 drivers/base/dd.c:882 > > bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514 > > device_add+0xae6/0x16f0 drivers/base/core.c:2114 > > usb_new_device.cold+0x6a4/0xe79 drivers/usb/core/hub.c:2536 > > hub_port_connect drivers/usb/core/hub.c:5098 [inline] > > hub_port_connect_change drivers/usb/core/hub.c:5213 [inline] > > port_event drivers/usb/core/hub.c:5359 [inline] > > hub_event+0x1b5c/0x3640 drivers/usb/core/hub.c:5441 > > process_one_work+0x92b/0x1530 kernel/workqueue.c:2269 > > worker_thread+0x96/0xe20 kernel/workqueue.c:2415 > > kthread+0x318/0x420 kernel/kthread.c:255 > > ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 > > > > The buggy address belongs to the object at ffff8881d21fc280 > > which belongs to the cache kmalloc-512 of size 512 > > The buggy address is located 88 bytes inside of > > 512-byte region [ffff8881d21fc280, ffff8881d21fc480) > > The buggy address belongs to the page: > > page:ffffea0007487f00 refcount:1 mapcount:0 mapping:ffff8881da002500 > > index:0x0 compound_mapcount: 0 > > flags: 0x200000000010200(slab|head) > > raw: 0200000000010200 ffffea000739fc80 0000000900000009 ffff8881da002500 > > raw: 0000000000000000 00000000000c000c 00000001ffffffff 0000000000000000 > > page dumped because: kasan: bad access detected > > > > Memory state around the buggy address: > > ffff8881d21fc180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ffff8881d21fc200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > > > ffff8881d21fc280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ^ > > ffff8881d21fc300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ffff8881d21fc380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ================================================================== > > I have tracked this bug down. The root causes lie in > usb_register_dev() and usb_deregister_dev(). > > The first problem is that usb_deregister_dev() sets > usb_minors[intf->minor] to NULL before calling device_destroy() on the > class device. This leaves a window during which another thread can > allocate the same minor number but will encounter a duplicate name > error when it tries to register its own class device. > > This error shows up in the kernel log from the syzbot test (not shown > in the bug report above, though): > > [ 120.583776][ T1775] sysfs: cannot create duplicate filename '/class/usbmisc/ldusb0' > > This can be fixed easily enough by reordering the statements in > usb_deregister_dev(). > > The second problem is in usb_register_dev(). When that routine runs, > it first allocates a minor number, then drops minor_rwsem, and then > creates the class device. If the device creation fails, the minor > number is deallocated and the whole routine returns an error. But > during the time while minor_rwsem was dropped, there is a window in > which the minor number is allocated and so another thread could > successfully open the device file! > > These two scenarios are exactly what happened during the syzbot test. > Minor number 0 was deallocated and then allocated in another thread. > The second allocation failed because the old class device was still in > existence. As a result of this failure, ldusb's private data structure > was released. Nevertheless, a third thread managed to open the device > file during the brief time that minor number 0 was re-allocated. When > that thread closed the file, it tried to access the private data > structure that had already been released. > > I believe the patch below will fix both problems. But you should take > a look at it first to see if it seems right; syzbot can't really test > the patch because it involves two separate races both coming out wrong! Ugh, nasty races, good find. Your fixes look fine, feel free to turn this into a patch I can submit and I will do so. thanks for finding this! greg k-h
