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

Kernel	Title	Rank 🛈	Repro	Count	Last	Reported	Patched	Status
upstream	KASAN: slab-out-of-bounds Read in fb_pad_aligned_buffer (2) fbdev	17		1	450d	444d	0/29	auto-obsoleted due to no activity on 2025/11/21 12:26
upstream	KASAN: slab-out-of-bounds Read in fb_pad_aligned_buffer fbdev	17		7	2336d	2481d	0/29	auto-closed as invalid on 2020/10/12 11:59
upstream	KASAN: slab-out-of-bounds Read in fb_pad_aligned_buffer (3) prio:high fbdev	17	C	6	36d	82d	0/29	upstream: reported C repro on 2026/08/16 14:48
linux-4.19	KASAN: slab-out-of-bounds Read in fb_pad_aligned_buffer	17		3	2397d	2474d	0/1	auto-closed as invalid on 2020/08/12 11:53
==================================================================
BUG: KASAN: slab-out-of-bounds in __fb_pad_aligned_buffer include/linux/fb.h:670 [inline]
BUG: KASAN: slab-out-of-bounds in fb_pad_aligned_buffer+0x554/0x5c0 drivers/video/fbdev/core/fbmem.c:117
Read of size 1 at addr ffff88807a5bd200 by task syz.5.2464/13508

CPU: 0 PID: 13508 Comm: syz.5.2464 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 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
 __fb_pad_aligned_buffer include/linux/fb.h:670 [inline]
 fb_pad_aligned_buffer+0x554/0x5c0 drivers/video/fbdev/core/fbmem.c:117
 cw_putcs_aligned drivers/video/fbdev/core/fbcon_cw.c:104 [inline]
 cw_putcs+0x14ca/0x18a0 drivers/video/fbdev/core/fbcon_cw.c:158
 fbcon_putcs+0x2c8/0x450 drivers/video/fbdev/core/fbcon.c:1265
 fbcon_putc+0x9b/0xe0 drivers/video/fbdev/core/fbcon.c:1275
 hide_softcursor drivers/tty/vt/vt.c:896 [inline]
 hide_cursor+0x24c/0x320 drivers/tty/vt/vt.c:908
 redraw_screen+0x1fc/0x1000 drivers/tty/vt/vt.c:1012
 fbcon_do_set_font+0x1402/0x1cd0 drivers/video/fbdev/core/fbcon.c:2417
 con_font_set drivers/tty/vt/vt.c:4669 [inline]
 con_font_op+0xace/0xdc0 drivers/tty/vt/vt.c:4715
 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:476 [inline]
 vt_ioctl+0x1618/0x1ca0 drivers/tty/vt/vt_ioctl.c:754
 tty_ioctl+0x848/0xc30 drivers/tty/tty_io.c:2810
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 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: 0033:0x7f5ee3b0c559
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:00007f5ee1d63028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5ee3d92fa0 RCX: 00007f5ee3b0c559
RDX: 0000200000000000 RSI: 0000000000004b72 RDI: 0000000000000003
RBP: 00007f5ee3ba3b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5ee3d93038 R14: 00007f5ee3d92fa0 R15: 00007ffc05759e88
 </TASK>

Allocated by task 6296:
 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_array include/linux/slab.h:647 [inline]
 fbcon_rotate_font+0x3d2/0xdd0 drivers/video/fbdev/core/fbcon_rotate.c:53
 fbcon_switch+0xcad/0x2040 drivers/video/fbdev/core/fbcon.c:2118
 redraw_screen+0x581/0x1000 drivers/tty/vt/vt.c:1021
 vc_do_resize+0x122c/0x17b0 drivers/tty/vt/vt.c:1342
 fbcon_modechanged+0x764/0x11d0 drivers/video/fbdev/core/fbcon.c:2693
 fbcon_rotate drivers/video/fbdev/core/fbcon.c:216 [inline]
 store_rotate+0x28f/0x420 drivers/video/fbdev/core/fbcon.c:3181
 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 ffff88807a5bc000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 512 bytes to the right of
 4096-byte region [ffff88807a5bc000, ffff88807a5bd000)
The buggy address belongs to the page:
page:ffffea0001e96e00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7a5b8
head:ffffea0001e96e00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 0000000300000001 ffff888017842140
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 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3571, ts 28260632080, free_ts 28258200990
 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]
 tomoyo_realpath_from_path+0xed/0x5e0 security/tomoyo/realpath.c:254
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_perm+0x23f/0x5d0 security/tomoyo/file.c:822
 security_inode_getattr+0xcf/0x120 security/security.c:1398
 vfs_getattr+0x26/0x3a0 fs/stat.c:157
 vfs_statx+0x146/0x4c0 fs/stat.c:225
 vfs_fstatat fs/stat.c:243 [inline]
 __do_sys_newfstatat fs/stat.c:411 [inline]
 __se_sys_newfstatat fs/stat.c:405 [inline]
 __x64_sys_newfstatat+0x15f/0x200 fs/stat.c:405
 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]
 kmem_cache_alloc+0x15d/0x280 mm/slub.c:3238
 getname_flags+0xb7/0x4f0 fs/namei.c:138
 user_path_at_empty+0x2a/0x190 fs/namei.c:2933
 user_path_at include/linux/namei.h:57 [inline]
 vfs_statx+0x107/0x4c0 fs/stat.c:221
 vfs_fstatat fs/stat.c:243 [inline]
 __do_sys_newfstatat fs/stat.c:411 [inline]
 __se_sys_newfstatat fs/stat.c:405 [inline]
 __x64_sys_newfstatat+0x15f/0x200 fs/stat.c:405
 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:
 ffff88807a5bd100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807a5bd180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807a5bd200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff88807a5bd280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807a5bd300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================