Re: [syzbot] [input?] [usb?] KASAN: slab-use-after-free Read in steam_input_open

Vicki Pfau
2025-02-23T11:45:42Z

Hi

On 2/22/25 9:01 AM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 0a86e49acfbb dt-bindings: usb: samsung,exynos-dwc3 Add exy..
> git tree: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> console output: https://syzkaller.appspot.com/x/log.txt?x=172e5ae4580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=f429368eda610a89
> dashboard link: https://syzkaller.appspot.com/bug?extid=0154da2d403396b2bd59
> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=162ca7f8580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17c02ba4580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f73104f0e203/disk-0a86e49a.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/fba41561bd74/vmlinux-0a86e49a.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/a82f1679cfc5/bzImage-0a86e49a.xz
>
> The issue was bisected to:
>
> commit 79504249d7e27cad4a3eeb9afc6386e418728ce0
> Author: Vicki Pfau <vi@endrift.com>
> Date: Wed Feb 5 03:55:27 2025 +0000
>
> HID: hid-steam: Move hidraw input (un)registering to work
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12f69fdf980000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=11f69fdf980000
> console output: https://syzkaller.appspot.com/x/log.txt?x=16f69fdf980000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+0154da2d403396b2bd59@syzkaller.appspotmail.com
> Fixes: 79504249d7e2 ("HID: hid-steam: Move hidraw input (un)registering to work")
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in steam_input_open+0x14d/0x160 drivers/hid/hid-steam.c:604
> Read of size 8 at addr ffff88810df35930 by task udevd/2958
>
> CPU: 0 UID: 0 PID: 2958 Comm: udevd Not tainted 6.14.0-rc3-syzkaller-00036-g0a86e49acfbb #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:94 [inline]
> dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
> print_address_description mm/kasan/report.c:378 [inline]
> print_report+0xc3/0x620 mm/kasan/report.c:489
> kasan_report+0xd9/0x110 mm/kasan/report.c:602
> steam_input_open+0x14d/0x160 drivers/hid/hid-steam.c:604
> input_open_device+0x230/0x390 drivers/input/input.c:600
> evdev_open_device drivers/input/evdev.c:391 [inline]
> evdev_open+0x52d/0x690 drivers/input/evdev.c:478
> chrdev_open+0x237/0x6a0 fs/char_dev.c:414
> do_dentry_open+0x6cb/0x1390 fs/open.c:956
> vfs_open+0x82/0x3f0 fs/open.c:1086
> do_open fs/namei.c:3830 [inline]
> path_openat+0x1e88/0x2d80 fs/namei.c:3989
> do_filp_open+0x20c/0x470 fs/namei.c:4016
> do_sys_openat2+0x17a/0x1e0 fs/open.c:1428
> do_sys_open fs/open.c:1443 [inline]
> __do_sys_openat fs/open.c:1459 [inline]
> __se_sys_openat fs/open.c:1454 [inline]
> __x64_sys_openat+0x175/0x210 fs/open.c:1454
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f48428969a4
> Code: 24 20 48 8d 44 24 30 48 89 44 24 28 64 8b 04 25 18 00 00 00 85 c0 75 2c 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 76 60 48 8b 15 55 a4 0d 00 f7 d8 64 89 02 48 83
> RSP: 002b:00007ffcc9566fe0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f48428969a4
> RDX: 0000000000080000 RSI: 00005564b5753fd0 RDI: 00000000ffffff9c
> RBP: 00005564b5753fd0 R08: 00005564b5708ed8 R09: 00007f4842971b10
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000080000
> R13: 00007ffcc95671a8 R14: 0000000000000000 R15: 00005564ab4c5ed5
> </TASK>
>
> Allocated by task 2986:
> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
> __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:394
> kasan_kmalloc include/linux/kasan.h:260 [inline]
> __do_kmalloc_node mm/slub.c:4294 [inline]
> __kmalloc_node_track_caller_noprof+0x20b/0x4c0 mm/slub.c:4313
> alloc_dr drivers/base/devres.c:119 [inline]
> devm_kmalloc+0xa5/0x260 drivers/base/devres.c:843
> devm_kzalloc include/linux/device.h:328 [inline]
> steam_probe+0x132/0x1060 drivers/hid/hid-steam.c:1241
> __hid_device_probe drivers/hid/hid-core.c:2713 [inline]
> hid_device_probe+0x349/0x700 drivers/hid/hid-core.c:2750
> call_driver_probe drivers/base/dd.c:579 [inline]
> really_probe+0x23e/0xa90 drivers/base/dd.c:658
> __driver_probe_device+0x1de/0x440 drivers/base/dd.c:800
> driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:830
> __device_attach_driver+0x1df/0x310 drivers/base/dd.c:958
> bus_for_each_drv+0x157/0x1e0 drivers/base/bus.c:462
> __device_attach+0x1e8/0x4b0 drivers/base/dd.c:1030
> bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
> device_add+0x114b/0x1a70 drivers/base/core.c:3665
> hid_add_device+0x374/0xa60 drivers/hid/hid-core.c:2896
> usbhid_probe+0xd32/0x1400 drivers/hid/usbhid/hid-core.c:1431
> usb_probe_interface+0x300/0x9c0 drivers/usb/core/driver.c:396
> call_driver_probe drivers/base/dd.c:579 [inline]
> really_probe+0x23e/0xa90 drivers/base/dd.c:658
> __driver_probe_device+0x1de/0x440 drivers/base/dd.c:800
> driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:830
> __device_attach_driver+0x1df/0x310 drivers/base/dd.c:958
> bus_for_each_drv+0x157/0x1e0 drivers/base/bus.c:462
> __device_attach+0x1e8/0x4b0 drivers/base/dd.c:1030
> bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
> device_add+0x114b/0x1a70 drivers/base/core.c:3665
> usb_set_configuration+0x10cb/0x1c50 drivers/usb/core/message.c:2210
> usb_generic_driver_probe+0xb1/0x110 drivers/usb/core/generic.c:250
> usb_probe_device+0xec/0x3e0 drivers/usb/core/driver.c:291
> call_driver_probe drivers/base/dd.c:579 [inline]
> really_probe+0x23e/0xa90 drivers/base/dd.c:658
> __driver_probe_device+0x1de/0x440 drivers/base/dd.c:800
> driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:830
> __device_attach_driver+0x1df/0x310 drivers/base/dd.c:958
> bus_for_each_drv+0x157/0x1e0 drivers/base/bus.c:462
> __device_attach+0x1e8/0x4b0 drivers/base/dd.c:1030
> bus_probe_device+0x17f/0x1c0 drivers/base/bus.c:537
> device_add+0x114b/0x1a70 drivers/base/core.c:3665
> usb_new_device+0xd09/0x1a20 drivers/usb/core/hub.c:2663
> hub_port_connect drivers/usb/core/hub.c:5533 [inline]
> hub_port_connect_change drivers/usb/core/hub.c:5673 [inline]
> port_event drivers/usb/core/hub.c:5833 [inline]
> hub_event+0x2e58/0x4f40 drivers/usb/core/hub.c:5915
> process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3236
> process_scheduled_works kernel/workqueue.c:3317 [inline]
> worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
> kthread+0x3af/0x750 kernel/kthread.c:464
> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> Freed by task 2986:
> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
> poison_slab_object mm/kasan/common.c:247 [inline]
> __kasan_slab_free+0x37/0x50 mm/kasan/common.c:264
> kasan_slab_free include/linux/kasan.h:233 [inline]
> slab_free_hook mm/slub.c:2353 [inline]
> slab_free mm/slub.c:4609 [inline]
> kfree+0x294/0x480 mm/slub.c:4757
> release_nodes+0x11e/0x240 drivers/base/devres.c:506
> devres_release_group+0x1be/0x2a0 drivers/base/devres.c:689
> hid_device_remove+0x107/0x260 drivers/hid/hid-core.c:2774
> device_remove+0xc8/0x170 drivers/base/dd.c:567
> __device_release_driver drivers/base/dd.c:1273 [inline]
> device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1296
> bus_remove_device+0x22f/0x420 drivers/base/bus.c:579
> device_del+0x396/0x9f0 drivers/base/core.c:3854
> hid_remove_device drivers/hid/hid-core.c:2953 [inline]
> hid_destroy_device+0x19c/0x240 drivers/hid/hid-core.c:2975
> usbhid_disconnect+0xa0/0xe0 drivers/hid/usbhid/hid-core.c:1458
> usb_unbind_interface+0x1e2/0x960 drivers/usb/core/driver.c:458
> device_remove drivers/base/dd.c:569 [inline]
> device_remove+0x122/0x170 drivers/base/dd.c:561
> __device_release_driver drivers/base/dd.c:1273 [inline]
> device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1296
> bus_remove_device+0x22f/0x420 drivers/base/bus.c:579
> device_del+0x396/0x9f0 drivers/base/core.c:3854
> usb_disable_device+0x36c/0x7f0 drivers/usb/core/message.c:1418
> usb_disconnect+0x2e1/0x920 drivers/usb/core/hub.c:2316
> hub_port_connect drivers/usb/core/hub.c:5373 [inline]
> hub_port_connect_change drivers/usb/core/hub.c:5673 [inline]
> port_event drivers/usb/core/hub.c:5833 [inline]
> hub_event+0x1bed/0x4f40 drivers/usb/core/hub.c:5915
> process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3236
> process_scheduled_works kernel/workqueue.c:3317 [inline]
> worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
> kthread+0x3af/0x750 kernel/kthread.c:464
> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> Last potentially related work creation:
> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> kasan_record_aux_stack+0x9b/0xb0 mm/kasan/generic.c:548
> insert_work+0x36/0x230 kernel/workqueue.c:2183
> __queue_work+0x97e/0x1080 kernel/workqueue.c:2339
> queue_work_on+0x11a/0x140 kernel/workqueue.c:2390
> hid_hw_close+0xaf/0xe0 drivers/hid/hid-core.c:2415
> drop_ref+0x2c8/0x390 drivers/hid/hidraw.c:346
> hidraw_disconnect+0x4b/0x60 drivers/hid/hidraw.c:642
> hid_disconnect+0x13e/0x1b0 drivers/hid/hid-core.c:2325
> hid_hw_stop+0x16/0x80 drivers/hid/hid-core.c:2370
> steam_remove+0x1af/0x220 drivers/hid/hid-steam.c:1326
> hid_device_remove+0xce/0x260 drivers/hid/hid-core.c:2769
> device_remove+0xc8/0x170 drivers/base/dd.c:567
> __device_release_driver drivers/base/dd.c:1273 [inline]
> device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1296
> bus_remove_device+0x22f/0x420 drivers/base/bus.c:579
> device_del+0x396/0x9f0 drivers/base/core.c:3854
> hid_remove_device drivers/hid/hid-core.c:2953 [inline]
> hid_destroy_device+0x19c/0x240 drivers/hid/hid-core.c:2975
> steam_remove+0xf0/0x220 drivers/hid/hid-steam.c:1334
> hid_device_remove+0xce/0x260 drivers/hid/hid-core.c:2769
> device_remove+0xc8/0x170 drivers/base/dd.c:567
> __device_release_driver drivers/base/dd.c:1273 [inline]
> device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1296
> bus_remove_device+0x22f/0x420 drivers/base/bus.c:579
> device_del+0x396/0x9f0 drivers/base/core.c:3854
> hid_remove_device drivers/hid/hid-core.c:2953 [inline]
> hid_destroy_device+0x19c/0x240 drivers/hid/hid-core.c:2975
> usbhid_disconnect+0xa0/0xe0 drivers/hid/usbhid/hid-core.c:1458
> usb_unbind_interface+0x1e2/0x960 drivers/usb/core/driver.c:458
> device_remove drivers/base/dd.c:569 [inline]
> device_remove+0x122/0x170 drivers/base/dd.c:561
> __device_release_driver drivers/base/dd.c:1273 [inline]
> device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1296
> bus_remove_device+0x22f/0x420 drivers/base/bus.c:579
> device_del+0x396/0x9f0 drivers/base/core.c:3854
> usb_disable_device+0x36c/0x7f0 drivers/usb/core/message.c:1418
> usb_disconnect+0x2e1/0x920 drivers/usb/core/hub.c:2316
> hub_port_connect drivers/usb/core/hub.c:5373 [inline]
> hub_port_connect_change drivers/usb/core/hub.c:5673 [inline]
> port_event drivers/usb/core/hub.c:5833 [inline]
> hub_event+0x1bed/0x4f40 drivers/usb/core/hub.c:5915
> process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3236
> process_scheduled_works kernel/workqueue.c:3317 [inline]
> worker_thread+0x6c8/0xf00 kernel/workqueue.c:3398
> kthread+0x3af/0x750 kernel/kthread.c:464
> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> Second to last potentially related work creation:
> kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
> kasan_record_aux_stack+0x9b/0xb0 mm/kasan/generic.c:548
> insert_work+0x36/0x230 kernel/workqueue.c:2183
> __queue_work+0x97e/0x1080 kernel/workqueue.c:2339
> queue_work_on+0x11a/0x140 kernel/workqueue.c:2390
> queue_work include/linux/workqueue.h:662 [inline]
> schedule_work include/linux/workqueue.h:723 [inline]
> steam_client_ll_open+0xab/0xf0 drivers/hid/hid-steam.c:1146
> hid_hw_open+0xe2/0x170 drivers/hid/hid-core.c:2392
> hidraw_open+0x274/0x7e0 drivers/hid/hidraw.c:308
> chrdev_open+0x237/0x6a0 fs/char_dev.c:414
> do_dentry_open+0x6cb/0x1390 fs/open.c:956
> vfs_open+0x82/0x3f0 fs/open.c:1086
> do_open fs/namei.c:3830 [inline]
> path_openat+0x1e88/0x2d80 fs/namei.c:3989
> do_filp_open+0x20c/0x470 fs/namei.c:4016
> do_sys_openat2+0x17a/0x1e0 fs/open.c:1428
> do_sys_open fs/open.c:1443 [inline]
> __do_sys_openat fs/open.c:1459 [inline]
> __se_sys_openat fs/open.c:1454 [inline]
> __x64_sys_openat+0x175/0x210 fs/open.c:1454
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> The buggy address belongs to the object at ffff88810df35800
> which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 304 bytes inside of
> freed 1024-byte region [ffff88810df35800, ffff88810df35c00)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10df30
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> flags: 0x200000000000040(head|node=0|zone=2)
> page_type: f5(slab)
> raw: 0200000000000040 ffff888100041dc0 dead000000000100 dead000000000122
> raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
> head: 0200000000000040 ffff888100041dc0 dead000000000100 dead000000000122
> head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
> head: 0200000000000003 ffffea000437cc01 ffffffffffffffff 0000000000000000
> head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 2964, tgid 2964 (kworker/0:4), ts 65532168704, free_ts 64378220826
> set_page_owner include/linux/page_owner.h:32 [inline]
> post_alloc_hook+0x181/0x1b0 mm/page_alloc.c:1551
> prep_new_page mm/page_alloc.c:1559 [inline]
> get_page_from_freelist+0xe76/0x2b90 mm/page_alloc.c:3477
> __alloc_frozen_pages_noprof+0x21c/0x2290 mm/page_alloc.c:4739
> alloc_pages_mpol+0xe7/0x410 mm/mempolicy.c:2270
> alloc_slab_page mm/slub.c:2423 [inline]
> allocate_slab mm/slub.c:2587 [inline]
> new_slab+0x23d/0x330 mm/slub.c:2640
> ___slab_alloc+0xc41/0x1670 mm/slub.c:3826
> __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3916
> __slab_alloc_node mm/slub.c:3991 [inline]
> slab_alloc_node mm/slub.c:4152 [inline]
> __do_kmalloc_node mm/slub.c:4293 [inline]
> __kmalloc_node_track_caller_noprof+0x157/0x4c0 mm/slub.c:4313
> alloc_dr drivers/base/devres.c:119 [inline]
> devm_kmalloc+0xa5/0x260 drivers/base/devres.c:843
> devm_kzalloc include/linux/device.h:328 [inline]
> steam_probe+0x132/0x1060 drivers/hid/hid-steam.c:1241
> __hid_device_probe drivers/hid/hid-core.c:2713 [inline]
> hid_device_probe+0x349/0x700 drivers/hid/hid-core.c:2750
> call_driver_probe drivers/base/dd.c:579 [inline]
> really_probe+0x23e/0xa90 drivers/base/dd.c:658
> __driver_probe_device+0x1de/0x440 drivers/base/dd.c:800
> driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:830
> __device_attach_driver+0x1df/0x310 drivers/base/dd.c:958
> bus_for_each_drv+0x157/0x1e0 drivers/base/bus.c:462
> page last free pid 2959 tgid 2959 stack trace:
> reset_page_owner include/linux/page_owner.h:25 [inline]
> free_pages_prepare mm/page_alloc.c:1127 [inline]
> free_frozen_pages+0x653/0xde0 mm/page_alloc.c:2660
> __put_partials+0x14c/0x170 mm/slub.c:3153
> qlink_free mm/kasan/quarantine.c:163 [inline]
> qlist_free_all+0x4e/0x120 mm/kasan/quarantine.c:179
> kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
> __kasan_slab_alloc+0x4e/0x70 mm/kasan/common.c:329
> kasan_slab_alloc include/linux/kasan.h:250 [inline]
> slab_post_alloc_hook mm/slub.c:4115 [inline]
> slab_alloc_node mm/slub.c:4164 [inline]
> kmem_cache_alloc_noprof+0x154/0x3b0 mm/slub.c:4171
> skb_clone+0x190/0x3f0 net/core/skbuff.c:2084
> do_one_broadcast net/netlink/af_netlink.c:1453 [inline]
> netlink_broadcast_filtered+0xb11/0xef0 net/netlink/af_netlink.c:1531
> netlink_broadcast+0x39/0x50 net/netlink/af_netlink.c:1555
> uevent_net_broadcast_untagged lib/kobject_uevent.c:331 [inline]
> kobject_uevent_net_broadcast lib/kobject_uevent.c:410 [inline]
> kobject_uevent_env+0xc69/0x1870 lib/kobject_uevent.c:608
> device_add+0x10e0/0x1a70 drivers/base/core.c:3646
> usb_set_configuration+0x10cb/0x1c50 drivers/usb/core/message.c:2210
> usb_generic_driver_probe+0xb1/0x110 drivers/usb/core/generic.c:250
> usb_probe_device+0xec/0x3e0 drivers/usb/core/driver.c:291
> call_driver_probe drivers/base/dd.c:579 [inline]
> really_probe+0x23e/0xa90 drivers/base/dd.c:658
> __driver_probe_device+0x1de/0x440 drivers/base/dd.c:800
>
> Memory state around the buggy address:
> ffff88810df35800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88810df35880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff88810df35900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff88810df35980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88810df35a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> ---
> 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 syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

This was reported internally a few days ago and I've been debugging this in the meantime. I have a tentative patch that I will submit in a day or two after we make sure it correctly fixes the issue. Though I'd previously tried getting it to reproduce in KASAN, I didn't have any luck; getting one of these backtraces was the final piece of the puzzle I was missing, so hopefully the fix is correct.

Vicki