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

Status: upstream: reported C repro on 2026/07/31 21:36
Reported-by: syzbot+af01eca8af586e44665c@syzkaller.appspotmail.com
First crash: 53d, last: 13d
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Read in fbcon_prepare_logo prio:high fbdev 19 syz, C 1873 12d 575d 18/29 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 27d 27d 0/3 upstream: reported on 2026/08/26 21:27
linux-6.6 KASAN: slab-out-of-bounds Read in fbcon_prepare_logo 19 4 17d 53d 0/2 upstream: reported on 2026/07/31 22:44

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+0x49a/0xda0 drivers/video/fbdev/core/fbcon.c:590
Read of size 218 at addr ffff88802431b4aa by task syz.0.17/4400

CPU: 1 PID: 4400 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x235/0x290 mm/kasan/generic.c:189
 memcpy+0x25/0x60 mm/kasan/shadow.c:65
 scr_memcpyw include/linux/vt_buffer.h:49 [inline]
 fbcon_prepare_logo+0x49a/0xda0 drivers/video/fbdev/core/fbcon.c:590
 fbcon_init+0x12f1/0x2310 drivers/video/fbdev/core/fbcon.c:1121
 visual_init+0x2dd/0x650 drivers/tty/vt/vt.c:1074
 do_bind_con_driver+0x859/0x1030 drivers/tty/vt/vt.c:3695
 vt_bind drivers/tty/vt/vt.c:3851 [inline]
 store_bind+0x794/0xa20 drivers/tty/vt/vt.c:3923
 kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2179 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fc750fd3159
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:00007ffe24b28478 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc75125afa0 RCX: 00007fc750fd3159
RDX: 0000000000000001 RSI: 0000200000000280 RDI: 0000000000000004
RBP: 00007fc75106a03b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc75125afac R14: 00007fc75125afa0 R15: 00007fc75125afa0
 </TASK>

Allocated by task 4400:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:612 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 vc_do_resize+0x36e/0x17b0 drivers/tty/vt/vt.c:1244
 fbcon_init+0x1309/0x2310 drivers/video/fbdev/core/fbcon.c:1118
 visual_init+0x2dd/0x650 drivers/tty/vt/vt.c:1074
 do_bind_con_driver+0x859/0x1030 drivers/tty/vt/vt.c:3695
 vt_bind drivers/tty/vt/vt.c:3851 [inline]
 store_bind+0x794/0xa20 drivers/tty/vt/vt.c:3923
 kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2179 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff88802431a000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1194 bytes to the right of
 4096-byte region [ffff88802431a000, ffff88802431b000)
The buggy address belongs to the page:
page:ffffea000090c600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x24318
head:ffffea000090c600 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888016c42140
raw: 0000000000000000 0000000080040004 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4400, ts 84002065314, free_ts 83983279350
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x807/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 __kmalloc+0x11d/0x340 mm/slub.c:4408
 kmalloc include/linux/slab.h:612 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 vc_do_resize+0x36e/0x17b0 drivers/tty/vt/vt.c:1244
 fbcon_startup+0x771/0xdc0 drivers/video/fbdev/core/fbcon.c:970
 do_bind_con_driver+0x356/0x1030 drivers/tty/vt/vt.c:3658
 vt_bind drivers/tty/vt/vt.c:3851 [inline]
 store_bind+0x794/0xa20 drivers/tty/vt/vt.c:3923
 kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2179 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 free_slab mm/slub.c:2020 [inline]
 discard_slab mm/slub.c:2026 [inline]
 __unfreeze_partials+0x188/0x1e0 mm/slub.c:2512
 put_cpu_partial+0x12d/0x190 mm/slub.c:2592
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xc0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 __kmalloc+0x189/0x340 mm/slub.c:4408
 kmalloc include/linux/slab.h:612 [inline]
 kernfs_fop_write_iter+0x14f/0x500 fs/kernfs/file.c:273
 call_write_iter include/linux/fs.h:2179 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Memory state around the buggy address:
 ffff88802431b380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802431b400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802431b480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                  ^
 ffff88802431b500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802431b580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/09 16:25 linux-5.15.y 0996e0926f6b 8387c273 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/09/09 21:22 linux-5.15.y 0996e0926f6b 4e8b1cc6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/09/09 09:48 linux-5.15.y 0996e0926f6b 8387c273 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/09/09 09:46 linux-5.15.y 0996e0926f6b 8387c273 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
2026/07/31 21:35 linux-5.15.y 6e2fd6534337 7664cf44 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in fbcon_prepare_logo
* Struck through repros no longer work on HEAD.