KASAN: slab-out-of-bounds Read in fbcon_prepare_logo

Status: upstream: reported on 2026/07/31 22:44
Reported-by: syzbot+d4e0b928d29b879239ae@syzkaller.appspotmail.com
First crash: 75d, last: 1h08m
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: slab-out-of-bounds Read in fbcon_prepare_logo 17 syz, C 7 8d01h 75d 0/3 upstream: reported C repro on 2026/07/31 21:36
upstream KASAN: slab-out-of-bounds Read in fbcon_prepare_logo prio:high fbdev 19 syz, C 1873 34d 596d 27/29 upstream: reported C repro on 2025/02/25 07:06
linux-6.1 KASAN: slab-out-of-bounds Read in fbcon_prepare_logo 17 2 49d 49d 0/3 upstream: reported on 2026/08/26 21:27

Sample crash report:
Console: switching to colour VGA+ 80x25
==================================================================
BUG: KASAN: slab-out-of-bounds in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: slab-out-of-bounds in fbcon_prepare_logo+0x4e2/0xa70 drivers/video/fbdev/core/fbcon.c:602
Read of size 218 at addr ffff88805aea94aa by task syz.7.4793/27521

CPU: 1 PID: 27521 Comm: syz.7.4793 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x241/0x290 mm/kasan/generic.c:187
 __asan_memcpy+0x29/0x70 mm/kasan/shadow.c:105
 scr_memcpyw include/linux/vt_buffer.h:49 [inline]
 fbcon_prepare_logo+0x4e2/0xa70 drivers/video/fbdev/core/fbcon.c:602
 fbcon_init+0x1380/0x2460 drivers/video/fbdev/core/fbcon.c:1137
 visual_init+0x2dd/0x650 drivers/tty/vt/vt.c:1023
 do_bind_con_driver+0x859/0x1030 drivers/tty/vt/vt.c:3645
 vt_bind drivers/tty/vt/vt.c:3801 [inline]
 store_bind+0x798/0xa20 drivers/tty/vt/vt.c:3873
 kernfs_fop_write_iter+0x3a4/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2018 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x474/0x9a0 fs/read_write.c:584
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc36119e559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc36207b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc361426180 RCX: 00007fc36119e559
RDX: 0000000000000001 RSI: 0000200000000280 RDI: 0000000000000004
RBP: 00007fc3612358b0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc361426218 R14: 00007fc361426180 R15: 00007ffd25c75d98
 </TASK>

Allocated by task 27521:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:198 [inline]
 __do_kmalloc_node mm/slab_common.c:1007 [inline]
 __kmalloc+0xb7/0x240 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 vc_do_resize+0x357/0x17f0 drivers/tty/vt/vt.c:1193
 fbcon_init+0x1399/0x2460 drivers/video/fbdev/core/fbcon.c:1134
 visual_init+0x2dd/0x650 drivers/tty/vt/vt.c:1023
 do_bind_con_driver+0x859/0x1030 drivers/tty/vt/vt.c:3645
 vt_bind drivers/tty/vt/vt.c:3801 [inline]
 store_bind+0x798/0xa20 drivers/tty/vt/vt.c:3873
 kernfs_fop_write_iter+0x3a4/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2018 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x474/0x9a0 fs/read_write.c:584
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88805aea8000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2020 bytes to the right of
 allocated 3270-byte region [ffff88805aea8000, ffff88805aea8cc6)

The buggy address belongs to the physical page:
page:ffffea00016baa00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5aea8
head:ffffea00016baa00 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888018842140 ffffea0000b2f800 dead000000000002
raw: 0000000000000000 0000000000040004 00000001ffffffff 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 0x1d2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 5978, tgid 5978 (kworker/u4:63), ts 1506680598982, free_ts 1506346532452
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
 prep_new_page mm/page_alloc.c:1589 [inline]
 get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
 __alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
 alloc_slab_page+0x5d/0x180 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:2081
 ___slab_alloc+0xc5c/0x12f0 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 __kmem_cache_alloc_node+0x11f/0x250 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc_node_track_caller+0xa4/0x230 mm/slab_common.c:1027
 kmalloc_reserve+0x116/0x240 net/core/skbuff.c:584
 __alloc_skb+0x138/0x2c0 net/core/skbuff.c:653
 alloc_skb include/linux/skbuff.h:1316 [inline]
 nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:748 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline]
 nsim_dev_trap_report_work+0x253/0xa90 drivers/net/netdevsim/dev.c:851
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1182 [inline]
 free_unref_page_prepare+0x7d7/0x8f0 mm/page_alloc.c:2366
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2459
 discard_slab mm/slub.c:2127 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
 put_cpu_partial+0x17c/0x250 mm/slub.c:2743
 __slab_free+0x319/0x400 mm/slub.c:3700
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:770
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x194/0x250 mm/slub.c:3534
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 __sk_attach_prog+0x53/0x400 net/core/filter.c:1469
 sk_attach_filter+0x4a/0x140 net/core/filter.c:1546
 sk_setsockopt+0x2226/0x2b20 net/core/sock.c:1320
 do_sock_setsockopt+0x11b/0x1a0 net/socket.c:2318
 __sys_setsockopt net/socket.c:2345 [inline]
 __do_sys_setsockopt net/socket.c:2354 [inline]
 __se_sys_setsockopt net/socket.c:2351 [inline]
 __x64_sys_setsockopt+0x182/0x200 net/socket.c:2351

Memory state around the buggy address:
 ffff88805aea9380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805aea9400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805aea9480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                  ^
 ffff88805aea9500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805aea9580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (11):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/15 04:47 linux-6.6.y a91a6aa9253c 8fb0ae89 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/10/11 10:38 linux-6.6.y a91a6aa9253c 4f92358f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/10/09 06:58 linux-6.6.y a91a6aa9253c b2734a59 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/10/09 06:37 linux-6.6.y a91a6aa9253c b2734a59 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/10/05 18:17 linux-6.6.y a91a6aa9253c af63e995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/08/30 19:43 linux-6.6.y a4a971135a2f 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/07/31 22:44 linux-6.6.y a1153c0deb44 7664cf44 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/10/11 10:37 linux-6.6.y a91a6aa9253c 4f92358f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in fbcon_prepare_logo
2026/10/09 06:37 linux-6.6.y a91a6aa9253c b2734a59 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KFENCE: out-of-bounds read in fbcon_prepare_logo
2026/09/05 16:00 linux-6.6.y 8b73de7da85f 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in fbcon_prepare_logo
2026/07/31 22:44 linux-6.6.y a1153c0deb44 7664cf44 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in fbcon_prepare_logo
* Struck through repros no longer work on HEAD.