Message-ID: <67bdace8.050a0220.bbfd1.00a6.GAE@google.com>
Date: Tue, 25 Feb 2025 03:43:36 -0800
From: syzbot <syzbot+0c815b25cdb3678e7083@...kaller.appspotmail.com>
To: deller@....de, dri-devel@...ts.freedesktop.org, 
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org, simona@...ll.ch, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fbdev?] KASAN: slab-out-of-bounds Read in fbcon_prepare_logo

syzbot has found a reproducer for the following issue on:

HEAD commit:    d082ecbc71e9 Linux 6.14-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14f56db0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b1635bf4c5557b92
dashboard link: https://syzkaller.appspot.com/bug?extid=0c815b25cdb3678e7083
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=172e77f8580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/323a5d590eec/disk-d082ecbc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f7c4b6e33fd9/vmlinux-d082ecbc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c518bbd55334/bzImage-d082ecbc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0c815b25cdb3678e7083@...kaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in scr_memcpyw include/linux/vt_buffer.h:38 [inline]
BUG: KASAN: slab-out-of-bounds in fbcon_prepare_logo+0xa15/0xc80 drivers/video/fbdev/core/fbcon.c:614
Read of size 256 at addr ffff888032edef60 by task syz.2.2428/8600

CPU: 0 UID: 0 PID: 8600 Comm: syz.2.2428 Not tainted 6.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xc3/0x670 mm/kasan/report.c:521
 kasan_report+0xd9/0x110 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189
 __asan_memcpy+0x23/0x60 mm/kasan/shadow.c:105
 scr_memcpyw include/linux/vt_buffer.h:38 [inline]
 fbcon_prepare_logo+0xa15/0xc80 drivers/video/fbdev/core/fbcon.c:614
 fbcon_init+0xd41/0x1890 drivers/video/fbdev/core/fbcon.c:1146
 visual_init+0x31d/0x620 drivers/tty/vt/vt.c:1011
 do_bind_con_driver.isra.0+0x57a/0xbf0 drivers/tty/vt/vt.c:3831
 vt_bind drivers/tty/vt/vt.c:3987 [inline]
 store_bind+0x61d/0x760 drivers/tty/vt/vt.c:4059
 dev_attr_store+0x55/0x80 drivers/base/core.c:2439
 sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
 kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:679
 ksys_write+0x12b/0x250 fs/read_write.c:731
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb44418d169
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:00007ffe52f027e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fb4443a5fa0 RCX: 00007fb44418d169
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fb44420e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb4443a5fa0 R14: 00007fb4443a5fa0 R15: 0000000000000003
 </TASK>

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x32edc
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000040 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
head: 00fff00000000040 0000000000000000 dead000000000122 0000000000000000
head: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
head: 00fff00000000002 ffffea0000cbb701 ffffffffffffffff 0000000000000000
head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x140dc0(GFP_USER|__GFP_COMP|__GFP_ZERO), pid 8600, tgid 8600 (syz.2.2428), ts 463971995066, free_ts 463963903452
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x181/0x1b0 mm/page_alloc.c:1551
 prep_new_page mm/page_alloc.c:1559 [inline]
 get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3477
 __alloc_frozen_pages_noprof+0x221/0x2470 mm/page_alloc.c:4739
 __alloc_pages_noprof+0xb/0x1b0 mm/page_alloc.c:4773
 __alloc_pages_node_noprof include/linux/gfp.h:265 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:292 [inline]
 ___kmalloc_large_node+0x84/0x1b0 mm/slub.c:4239
 __kmalloc_large_node_noprof+0x1c/0x70 mm/slub.c:4266
 __do_kmalloc_node mm/slub.c:4282 [inline]
 __kmalloc_noprof.cold+0xc/0x61 mm/slub.c:4306
 kmalloc_noprof include/linux/slab.h:905 [inline]
 kzalloc_noprof include/linux/slab.h:1037 [inline]
 vc_do_resize+0x1e3/0x10f0 drivers/tty/vt/vt.c:1174
 vc_resize include/linux/vt_kern.h:49 [inline]
 fbcon_init+0xd1d/0x1890 drivers/video/fbdev/core/fbcon.c:1143
 visual_init+0x31d/0x620 drivers/tty/vt/vt.c:1011
 do_bind_con_driver.isra.0+0x57a/0xbf0 drivers/tty/vt/vt.c:3831
 vt_bind drivers/tty/vt/vt.c:3987 [inline]
 store_bind+0x61d/0x760 drivers/tty/vt/vt.c:4059
 dev_attr_store+0x55/0x80 drivers/base/core.c:2439
 sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
 kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:679
page last free pid 8600 tgid 8600 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 free_frozen_pages+0x6db/0xfb0 mm/page_alloc.c:2660
 __folio_put+0x32a/0x450 mm/swap.c:112
 vc_do_resize+0xe31/0x10f0 drivers/tty/vt/vt.c:1194
 vc_resize include/linux/vt_kern.h:49 [inline]
 fbcon_startup+0x406/0xb70 drivers/video/fbdev/core/fbcon.c:997
 do_bind_con_driver.isra.0+0x207/0xbf0 drivers/tty/vt/vt.c:3794
 vt_bind drivers/tty/vt/vt.c:3987 [inline]
 store_bind+0x61d/0x760 drivers/tty/vt/vt.c:4059
 dev_attr_store+0x55/0x80 drivers/base/core.c:2439
 sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
 kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:679
 ksys_write+0x12b/0x250 fs/read_write.c:731
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888032edef00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888032edef80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888032edf000: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
                   ^
 ffff888032edf080: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 ffff888032edf100: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
==================================================================


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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