[moderation] [fbdev?] KASAN: slab-out-of-bounds Read in fb_pad_unaligned_buffer (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2aeda9592360 Add linux-next specific files for 20250627
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13f4f08c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9e7e53eaffada5f7
dashboard link: https://syzkaller.appspot.com/bug?extid=6a342082dad1565674ad
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [del...@gmx.de dri-...@lists.freedesktop.org linux...@vger.kernel.org linux-...@vger.kernel.org sim...@ffwll.ch]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/341223d6a48c/disk-2aeda959.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5668296f18f2/vmlinux-2aeda959.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c11200402e5c/bzImage-2aeda959.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6a3420...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in fb_pad_unaligned_buffer+0x420/0x500 drivers/video/fbdev/core/fbmem.c:118
Read of size 1 at addr ffff88802fa7ab10 by task syz.1.2501/14099

CPU: 0 UID: 0 PID: 14099 Comm: syz.1.2501 Not tainted 6.16.0-rc3-next-20250627-syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:408 [inline]
print_report+0xd2/0x2b0 mm/kasan/report.c:521
kasan_report+0x118/0x150 mm/kasan/report.c:634
fb_pad_unaligned_buffer+0x420/0x500 drivers/video/fbdev/core/fbmem.c:118
bit_putcs_unaligned drivers/video/fbdev/core/bitblit.c:129 [inline]
bit_putcs+0x950/0x1a50 drivers/video/fbdev/core/bitblit.c:187
fbcon_putcs+0x3e2/0x5f0 drivers/video/fbdev/core/fbcon.c:1315
con_flush drivers/tty/vt/vt.c:2746 [inline]
do_con_write+0x2835/0x5200 drivers/tty/vt/vt.c:3173
con_write+0x24/0x40 drivers/tty/vt/vt.c:3516
process_output_block drivers/tty/n_tty.c:561 [inline]
n_tty_write+0xd32/0x11d0 drivers/tty/n_tty.c:2377
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write+0x503/0x990 drivers/tty/tty_io.c:1081
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x54b/0xa90 fs/read_write.c:686
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f400a38e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f400b29a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f400a5b6080 RCX: 00007f400a38e929
RDX: 0000000000001006 RSI: 0000200000001980 RDI: 000000000000000f
RBP: 00007f400a410b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f400a5b6080 R15: 00007ffd02bf75e8
</TASK>

Allocated by task 6064:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4365 [inline]
__kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4377
kmalloc_noprof include/linux/slab.h:909 [inline]
fbcon_set_font+0x519/0xe90 drivers/video/fbdev/core/fbcon.c:2523
con_font_set drivers/tty/vt/vt.c:4887 [inline]
con_font_op+0xcac/0x1070 drivers/tty/vt/vt.c:4934
vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline]
vt_ioctl+0x1a8a/0x1f00 drivers/tty/vt/vt_ioctl.c:751
tty_ioctl+0x929/0xde0 drivers/tty/tty_io.c:2792
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802fa7a800
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 0 bytes to the right of
allocated 784-byte region [ffff88802fa7a800, ffff88802fa7ab10)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2fa78
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a841dc0 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a841dc0 0000000000000000 dead000000000001
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0000be9e01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 44, tgid 44 (kworker/u8:3), ts 80808073972, free_ts 80664757748
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1848
prep_new_page mm/page_alloc.c:1856 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3855
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5145
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
alloc_slab_page mm/slub.c:2487 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2655
new_slab mm/slub.c:2709 [inline]
___slab_alloc+0xbeb/0x1410 mm/slub.c:3891
__slab_alloc mm/slub.c:3981 [inline]
__slab_alloc_node mm/slub.c:4056 [inline]
slab_alloc_node mm/slub.c:4217 [inline]
__do_kmalloc_node mm/slub.c:4364 [inline]
__kmalloc_noprof+0x305/0x4f0 mm/slub.c:4377
kmalloc_noprof include/linux/slab.h:909 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
ieee802_11_parse_elems_full+0x152/0x2b20 net/mac80211/parse.c:1013
ieee802_11_parse_elems_crc net/mac80211/ieee80211_i.h:2418 [inline]
ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2425 [inline]
ieee80211_inform_bss+0x10c/0x10a0 net/mac80211/scan.c:79
rdev_inform_bss net/wireless/rdev-ops.h:418 [inline]
cfg80211_inform_single_bss_data+0xd05/0x1ac0 net/wireless/scan.c:2367
cfg80211_inform_bss_data+0x1fb/0x3b20 net/wireless/scan.c:3222
cfg80211_inform_bss_frame_data+0x3d7/0x730 net/wireless/scan.c:3313
ieee80211_bss_info_update+0x746/0x9e0 net/mac80211/scan.c:226
ieee80211_rx_bss_info net/mac80211/ibss.c:1094 [inline]
ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1573 [inline]
ieee80211_ibss_rx_queued_mgmt+0xa36/0x2ae0 net/mac80211/ibss.c:1600
ieee80211_iface_process_skb net/mac80211/iface.c:1668 [inline]
ieee80211_iface_work+0x806/0xfe0 net/mac80211/iface.c:1722
cfg80211_wiphy_work+0x2df/0x460 net/wireless/core.c:435
page last free pid 6046 tgid 6046 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1392 [inline]
__free_frozen_pages+0xb80/0xd80 mm/page_alloc.c:2892
discard_slab mm/slub.c:2753 [inline]
__put_partials+0x156/0x1a0 mm/slub.c:3218
put_cpu_partial+0x17c/0x250 mm/slub.c:3293
__slab_free+0x2d5/0x3c0 mm/slub.c:4550
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:329
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4180 [inline]
slab_alloc_node mm/slub.c:4229 [inline]
kmem_cache_alloc_noprof+0x1c1/0x3c0 mm/slub.c:4236
getname_flags+0xb8/0x540 fs/namei.c:146
getname include/linux/fs.h:2909 [inline]
getname_maybe_null include/linux/fs.h:2916 [inline]
vfs_fstatat+0x43/0x170 fs/stat.c:370
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat fs/stat.c:536 [inline]
__x64_sys_newfstatat+0x116/0x190 fs/stat.c:536
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88802fa7aa00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88802fa7aa80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88802fa7ab00: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88802fa7ab80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802fa7ac00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

Sending this report to the next reporting stage.