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

Status: upstream: reported on 2026/07/24 00:48
Reported-by: syzbot+1c89534b655bcf1739e4@syzkaller.appspotmail.com
First crash: 99d, last: 2d04h
▶ ▼ Similar bugs (14)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor (2) 17 syz, C done 8 1988d 2110d 1/1 fixed on 2021/06/23 17:43
linux-4.14 KASAN: slab-out-of-bounds Read in soft_cursor 17 syz, C unreliable 57 1992d 2523d 0/1 upstream: reported C repro on 2019/12/03 14:54
linux-5.15 KASAN: slab-out-of-bounds Read in soft_cursor 17 1 37d 37d 0/3 upstream: reported on 2026/09/23 15:50
linux-4.19 KASAN: slab-out-of-bounds Read in soft_cursor 17 syz, C done 61 2185d 2524d 1/1 fixed on 2020/12/05 19:30
upstream KASAN: slab-out-of-bounds Read in soft_cursor (2) fbdev 17 9 270d 404d 0/29 auto-obsoleted due to no activity on 2026/05/14 02:42
upstream KASAN: slab-out-of-bounds Read in soft_cursor fbdev 17 syz, C done 218 2214d 2522d 15/29 fixed on 2020/11/16 12:12
linux-6.6 KASAN: slab-out-of-bounds Read in soft_cursor 17 2 25d 25d 0/2 upstream: reported on 2026/10/05 14:46
upstream KASAN: global-out-of-bounds Read in soft_cursor (3) fbdev 19 223 17h33m 85d 28/29 upstream: reported on 2026/08/07 00:01
linux-5.15 KASAN: null-ptr-deref Read in soft_cursor origin:lts-only 11 syz error 1 1252d 1252d 0/3 auto-obsoleted due to no activity on 2024/12/24 15:39
linux-4.14 KASAN: use-after-free Read in soft_cursor 19 syz, C inconclusive 7 2012d 2523d 0/1 upstream: reported C repro on 2019/12/04 13:11
upstream general protection fault in soft_cursor fbdev 11 syz, C 3 1253d 1253d 22/29 fixed on 2023/07/01 16:05
upstream KASAN: global-out-of-bounds Read in soft_cursor (2) fbdev 17 1 616d 612d 0/29 auto-obsoleted due to no activity on 2025/05/23 01:13
linux-4.19 KASAN: global-out-of-bounds Read in soft_cursor 17 syz, C done 22 1985d 2452d 1/1 fixed on 2021/06/24 08:01
linux-4.14 KASAN: global-out-of-bounds Read in soft_cursor 17 syz, C error 19 1512d 2511d 0/1 upstream: reported C repro on 2019/12/16 00:09

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in soft_cursor+0x37b/0xc30 drivers/video/fbdev/core/softcursor.c:70
Read of size 24 at addr ffff88802787d068 by task syz.3.552/7362

CPU: 1 PID: 7362 Comm: syz.3.552 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 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
 soft_cursor+0x37b/0xc30 drivers/video/fbdev/core/softcursor.c:70
 cw_cursor+0x1f4f/0x2b20 drivers/video/fbdev/core/fbcon_cw.c:363
 hide_cursor+0x7f/0x320 drivers/tty/vt/vt.c:907
 redraw_screen+0x1fc/0x1000 drivers/tty/vt/vt.c:1012
 vc_do_resize+0x122c/0x17b0 drivers/tty/vt/vt.c:1342
 fbcon_do_set_font+0xb5c/0x1ae0 drivers/video/fbdev/core/fbcon.c:2437
 con_font_set drivers/tty/vt/vt.c:4678 [inline]
 con_font_op+0xac1/0xdb0 drivers/tty/vt/vt.c:4724
 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:476 [inline]
 vt_ioctl+0x161e/0x1ca0 drivers/tty/vt/vt_ioctl.c:754
 tty_ioctl+0x7e6/0xba0 drivers/tty/tty_io.c:2776
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1fb459f559
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:00007f1fb27f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1fb4825fa0 RCX: 00007f1fb459f559
RDX: 0000200000000700 RSI: 0000000000004b72 RDI: 0000000000000003
RBP: 00007f1fb4636b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1fb4826038 R14: 00007f1fb4825fa0 R15: 00007ffc90fde738
 </TASK>

Allocated by task 6388:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:936 [inline]
 __kmalloc+0xb3/0x240 mm/slab_common.c:949
 kmalloc_array include/linux/slab.h:615 [inline]
 fbcon_rotate_font+0x3d2/0xdd0 drivers/video/fbdev/core/fbcon_rotate.c:53
 fbcon_switch+0xdf5/0x1f80 drivers/video/fbdev/core/fbcon.c:2145
 redraw_screen+0x581/0x1000 drivers/tty/vt/vt.c:1021
 vc_do_resize+0x122c/0x17b0 drivers/tty/vt/vt.c:1342
 fbcon_modechanged+0x80d/0x12b0 drivers/video/fbdev/core/fbcon.c:2719
 fbcon_rotate drivers/video/fbdev/core/fbcon.c:226 [inline]
 store_rotate+0x329/0x4f0 drivers/video/fbdev/core/fbcon.c:3235
 kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2271 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x482/0x9a0 fs/read_write.c:584
 ksys_write+0x14d/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88802787c000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 104 bytes to the right of
 4096-byte region [ffff88802787c000, ffff88802787d000)

The buggy address belongs to the physical page:
page:ffffea00009e1e00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x27878
head:ffffea00009e1e00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000001 ffff888018442140
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 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 11, tgid 11 (kworker/u4:1), ts 318680449841, free_ts 318465886931
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2560
 prep_new_page mm/page_alloc.c:2567 [inline]
 get_page_from_freelist+0x206b/0x2180 mm/page_alloc.c:4358
 __alloc_pages+0x1ec/0x4f0 mm/page_alloc.c:5658
 alloc_slab_page+0x5d/0x180 mm/slub.c:1799
 allocate_slab mm/slub.c:1944 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:1997
 ___slab_alloc+0xbc5/0x1240 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 __kmem_cache_alloc_node+0x126/0x270 mm/slub.c:3398
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc_node_track_caller+0xa0/0x240 mm/slab_common.c:956
 kmalloc_reserve net/core/skbuff.c:446 [inline]
 __alloc_skb+0x226/0x7d0 net/core/skbuff.c:515
 alloc_skb include/linux/skbuff.h:1303 [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+0x24f/0xa80 drivers/net/netdevsim/dev.c:851
 process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1487 [inline]
 free_pcp_prepare mm/page_alloc.c:1537 [inline]
 free_unref_page_prepare+0x8e5/0x9e0 mm/page_alloc.c:3414
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3509
 qlink_free mm/kasan/quarantine.c:168 [inline]
 qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
 kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
 __kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:201 [inline]
 slab_post_alloc_hook+0x4b/0x490 mm/slab.h:737
 slab_alloc_node mm/slub.c:3359 [inline]
 slab_alloc mm/slub.c:3367 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3374 [inline]
 kmem_cache_alloc_lru+0x182/0x2e0 mm/slub.c:3390
 alloc_inode_sb include/linux/fs.h:3278 [inline]
 sock_alloc_inode+0x24/0xc0 net/socket.c:306
 alloc_inode fs/inode.c:261 [inline]
 new_inode_pseudo+0x5f/0x1c0 fs/inode.c:1063
 sock_alloc net/socket.c:631 [inline]
 __sock_create+0x129/0x940 net/socket.c:1514
 rds_tcp_conn_path_connect+0x2ab/0x6e0 net/rds/tcp_connect.c:-1
 rds_connect_worker+0x1ce/0x280 net/rds/threads.c:176
 process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Memory state around the buggy address:
 ffff88802787cf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88802787cf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88802787d000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                          ^
 ffff88802787d080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802787d100: 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
2026/10/29 09:37 linux-6.1.y 79807e970724 b1d00f76 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in soft_cursor
2026/10/14 03:29 linux-6.1.y a500ba24937a 7321cd29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/14 02:36 linux-6.1.y e4f7d8be268e b13552fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in soft_cursor
2026/07/24 00:48 linux-6.1.y 090666d3cc90 544adce9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in soft_cursor
2026/08/25 16:55 linux-6.1.y 05208478041c a9a1fc32 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in soft_cursor
* Struck through repros no longer work on HEAD.