KASAN: slab-use-after-free Read in virtqueue_add

Status: moderation: reported on 2026/08/10 00:24
Subsystems: virt
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+2dcadf8f87e35bbd35fa@syzkaller.appspotmail.com
First crash: 6d04h, last: 6d04h
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
907aea10 repro-c 💥 KASAN: slab-use-after-free Read in virtqueue_add 2026/08/10 07:52 2026/08/10 08:03 2026/08/10 13:38 5d63f80b
b0ed8704 moderation Actionable: ❌ ❓ KASAN: slab-use-after-free Read in virtqueue_add 2026/08/10 00:29 2026/08/10 00:29 2026/08/10 01:53 5d63f80b
2bec433b assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ✅ ❓ KASAN: slab-use-after-free Read in virtqueue_add 2026/08/09 12:12 2026/08/09 12:12 2026/08/09 12:19 5d63f80b
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KMSAN: uninit-value in virtqueue_add (3) virt 7 13 1375d 1668d 0/29 auto-obsoleted due to no activity on 2023/02/12 03:53
upstream KMSAN: uninit-value in virtqueue_add (5) virt 7 170 787d 786d 0/29 auto-obsoleted due to no activity on 2024/08/23 15:10
upstream KMSAN: kernel-infoleak in _copy_to_iter (8) mm 21 syz, C 21180 1159d 1253d 22/29 fixed on 2023/06/08 14:41
android-54 KASAN: use-after-free Read in virtqueue_add 19 syz, C 2 642d 1884d 0/2 upstream: reported C repro on 2021/06/13 11:51
upstream KMSAN: uninit-value in virtqueue_add (4) mm 7 syz, C 203184 790d 952d 25/29 fixed on 2024/06/11 10:02

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in virtqueue_add+0x2200/0x2960 drivers/virtio/virtio_ring.c:2839
Read of size 4 at addr ffff888025a84648 by task syz-executor/5624

CPU: 0 UID: 0 PID: 5624 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 virtqueue_add+0x2200/0x2960 drivers/virtio/virtio_ring.c:2839
 virtqueue_add_sgs+0x17f/0x1a0 drivers/virtio/virtio_ring.c:2878
 __virtscsi_add_cmd drivers/scsi/virtio_scsi.c:475 [inline]
 virtscsi_add_cmd+0x4f2/0x660 drivers/scsi/virtio_scsi.c:509
 virtscsi_queuecommand+0x6be/0xb80 drivers/scsi/virtio_scsi.c:606
 scsi_dispatch_cmd drivers/scsi/scsi_lib.c:1671 [inline]
 scsi_queue_rq+0x188a/0x33a0 drivers/scsi/scsi_lib.c:1928
 blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2117
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
 blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
 __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307
 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
 blk_mq_run_hw_queue+0x404/0x4f0 block/blk-mq.c:2356
 blk_mq_dispatch_list+0xd11/0xe10 include/linux/spinlock.h:-1
 blk_mq_flush_plug_list+0x45f/0x540 block/blk-mq.c:2966
 __blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1266
 blk_finish_plug+0x5d/0x80 block/blk-core.c:1293
 read_pages+0x3c2/0x5a0 mm/readahead.c:187
 page_cache_ra_unbounded+0x425/0x9d0 mm/readahead.c:282
 do_page_cache_ra mm/readahead.c:348 [inline]
 page_cache_ra_order+0xb47/0xee0 mm/readahead.c:558
 do_sync_mmap_readahead+0x75e/0x990 mm/filemap.c:3428
 filemap_fault+0x7d9/0x13b0 mm/filemap.c:3582
 __do_fault+0x138/0x2a0 mm/memory.c:5425
 do_read_fault mm/memory.c:5860 [inline]
 do_fault mm/memory.c:5994 [inline]
 do_pte_missing+0x2215/0x34b0 mm/memory.c:4566
 handle_pte_fault mm/memory.c:6379 [inline]
 __handle_mm_fault mm/memory.c:6517 [inline]
 handle_mm_fault+0x1b36/0x3080 mm/memory.c:6686
 do_user_addr_fault+0xa4d/0x1340 arch/x86/mm/fault.c:1343
 handle_page_fault arch/x86/mm/fault.c:1483 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
RIP: 0033:0x7f468b159195
Code: Unable to access opcode bytes at 0x7f468b15916b.
RSP: 002b:00007fffeeaeaec0 EFLAGS: 00010202
RAX: 000000000000003d RBX: 0000555562e55500 RCX: 00007f468b159197
RDX: 0000000040000000 RSI: 00007fffeeaeaf1c RDI: ffffffffffffffff
RBP: 00007fffeeaeaf1c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000008
R13: 0000000000000003 R14: 00007fffeeaeb178 R15: 0000000000000000
 </TASK>

Allocated by task 152:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x32d/0x660 mm/slub.c:5489
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 set_mm_walk mm/vmscan.c:3802 [inline]
 try_to_inc_max_seq+0x1f2/0x10e0 mm/vmscan.c:4023
 try_to_shrink_lruvec+0xb0f/0xed0 mm/vmscan.c:4977
 shrink_one+0x233/0x730 mm/vmscan.c:5024
 shrink_many mm/vmscan.c:5087 [inline]
 lru_gen_shrink_node mm/vmscan.c:5165 [inline]
 shrink_node+0x3303/0x3b60 mm/vmscan.c:6154
 shrink_zones mm/vmscan.c:6410 [inline]
 do_try_to_free_pages+0x6a3/0x1990 mm/vmscan.c:6472
 try_to_free_pages+0x90a/0xe50 mm/vmscan.c:6711
 __perform_reclaim mm/page_alloc.c:4405 [inline]
 __alloc_pages_direct_reclaim+0x148/0x310 mm/page_alloc.c:4427
 __alloc_pages_slowpath+0x59d/0xcc0 mm/page_alloc.c:4876
 __alloc_frozen_pages_noprof+0x31f/0x380 mm/page_alloc.c:5317
 alloc_pages_mpol+0x212/0x380 mm/mempolicy.c:2490
 alloc_frozen_pages_noprof mm/mempolicy.c:2561 [inline]
 alloc_pages_noprof+0xac/0x2a0 mm/mempolicy.c:2581
 stack_depot_save_flags+0x735/0x800 lib/stackdepot.c:685
 kasan_save_stack mm/kasan/common.c:58 [inline]
 kasan_save_track+0x4f/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5334 [inline]
 __kmalloc_noprof+0x375/0x720 mm/slub.c:5359
 _kmalloc_noprof include/linux/slab.h:992 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 vp_request_msix_vectors drivers/virtio/virtio_pci_common.c:141 [inline]
 vp_find_vqs_msix+0x4b8/0xd00 drivers/virtio/virtio_pci_common.c:414
 vp_find_vqs+0xce/0x790 drivers/virtio/virtio_pci_common.c:531
 virtio_find_vqs include/linux/virtio_config.h:298 [inline]
 virtnet_find_vqs drivers/net/virtio_net.c:6473 [inline]
 init_vqs+0xad6/0x11c0 drivers/net/virtio_net.c:6555
 virtnet_restore_up drivers/net/virtio_net.c:5740 [inline]
 virtnet_restore+0x4b/0xb70 drivers/net/virtio_net.c:7202
 virtio_device_restore_priv+0x381/0x690 drivers/virtio/virtio.c:633
 dpm_run_callback+0x84/0x2a0 drivers/base/power/main.c:510
 device_resume+0x8f7/0xa30 drivers/base/power/main.c:1178
 async_resume+0x20/0x30 drivers/base/power/main.c:1201
 async_run_entry_fn+0x9d/0x430 kernel/async.c:129
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 152:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2677 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x1c5/0x640 mm/slub.c:6692
 lru_gen_shrink_node mm/vmscan.c:5170 [inline]
 shrink_node+0x370b/0x3b60 mm/vmscan.c:6154
 shrink_zones mm/vmscan.c:6410 [inline]
 do_try_to_free_pages+0x6a3/0x1990 mm/vmscan.c:6472
 try_to_free_pages+0x90a/0xe50 mm/vmscan.c:6711
 __perform_reclaim mm/page_alloc.c:4405 [inline]
 __alloc_pages_direct_reclaim+0x148/0x310 mm/page_alloc.c:4427
 __alloc_pages_slowpath+0x59d/0xcc0 mm/page_alloc.c:4876
 __alloc_frozen_pages_noprof+0x31f/0x380 mm/page_alloc.c:5317
 alloc_pages_mpol+0x212/0x380 mm/mempolicy.c:2490
 alloc_frozen_pages_noprof mm/mempolicy.c:2561 [inline]
 alloc_pages_noprof+0xac/0x2a0 mm/mempolicy.c:2581
 stack_depot_save_flags+0x735/0x800 lib/stackdepot.c:685
 kasan_save_stack mm/kasan/common.c:58 [inline]
 kasan_save_track+0x4f/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5334 [inline]
 __kmalloc_noprof+0x375/0x720 mm/slub.c:5359
 _kmalloc_noprof include/linux/slab.h:992 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 vp_request_msix_vectors drivers/virtio/virtio_pci_common.c:141 [inline]
 vp_find_vqs_msix+0x4b8/0xd00 drivers/virtio/virtio_pci_common.c:414
 vp_find_vqs+0xce/0x790 drivers/virtio/virtio_pci_common.c:531
 virtio_find_vqs include/linux/virtio_config.h:298 [inline]
 virtnet_find_vqs drivers/net/virtio_net.c:6473 [inline]
 init_vqs+0xad6/0x11c0 drivers/net/virtio_net.c:6555
 virtnet_restore_up drivers/net/virtio_net.c:5740 [inline]
 virtnet_restore+0x4b/0xb70 drivers/net/virtio_net.c:7202
 virtio_device_restore_priv+0x381/0x690 drivers/virtio/virtio.c:633
 dpm_run_callback+0x84/0x2a0 drivers/base/power/main.c:510
 device_resume+0x8f7/0xa30 drivers/base/power/main.c:1178
 async_resume+0x20/0x30 drivers/base/power/main.c:1201
 async_run_entry_fn+0x9d/0x430 kernel/async.c:129
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff888025a84600
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 72 bytes inside of
 freed 256-byte region [ffff888025a84600, ffff888025a84700)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x25a84
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b001b40 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b001b40 dead000000000100 dead000000000122
head: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffffffffffff81 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 5963958113, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1859
 prep_new_page mm/page_alloc.c:1867 [inline]
 get_page_from_freelist+0x21fa/0x2270 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
 alloc_slab_page mm/slub.c:3266 [inline]
 allocate_slab+0x79/0x5e0 mm/slub.c:3380
 new_slab mm/slub.c:3426 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7310
 refill_sheaf mm/slub.c:2804 [inline]
 __pcs_replace_empty_main+0x2bf/0x6b0 mm/slub.c:4675
 alloc_from_pcs mm/slub.c:4773 [inline]
 slab_alloc_node mm/slub.c:4905 [inline]
 __kmalloc_cache_noprof+0x3a7/0x660 mm/slub.c:5485
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 bus_add_driver+0x162/0x670 drivers/base/bus.c:747
 driver_register+0x23a/0x320 drivers/base/driver.c:174
 do_one_initcall+0x250/0x870 init/main.c:1347
 do_initcall_level+0x10a/0x1a0 init/main.c:1409
 do_initcalls+0x59/0xa0 init/main.c:1425
 kernel_init_freeable+0x29d/0x3e0 init/main.c:1658
 kernel_init+0x1d/0x1d0 init/main.c:1548
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888025a84500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888025a84580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888025a84600: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff888025a84680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888025a84700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/04 16:16 upstream 848acc8ffe1b d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in virtqueue_add
* Struck through repros no longer work on HEAD.