Re: [syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in fillrect

[syzbot <syzbot+7a63ce155648954e749b@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    6628e7d4c6b2 Linux 7.4-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14484581580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1d2c97eac7d33533
dashboard link: https://syzkaller.appspot.com/bug?extid=7a63ce155648954e749b
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=126c692d580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=140f1d59580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-6628e7d4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2f9e962fc6ac/vmlinux-6628e7d4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/192b99738db6/bzImage-6628e7d4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7a63ce155648954e749b@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
BUG: KASAN: vmalloc-out-of-bounds in bitfill drivers/video/fbdev/core/fb_fillrect.h:133 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_fillrect_static drivers/video/fbdev/core/fb_fillrect.h:219 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_fillrect drivers/video/fbdev/core/fb_fillrect.h:278 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_fillrect+0x174a/0x1910 drivers/video/fbdev/core/sysfillrect.c:24
Write of size 8 at addr ffffc900056fd000 by task syz.0.17/5992

CPU: 3 UID: 0 PID: 5992 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
 bitfill drivers/video/fbdev/core/fb_fillrect.h:133 [inline]
 fb_fillrect_static drivers/video/fbdev/core/fb_fillrect.h:219 [inline]
 fb_fillrect drivers/video/fbdev/core/fb_fillrect.h:278 [inline]
 sys_fillrect+0x174a/0x1910 drivers/video/fbdev/core/sysfillrect.c:24
 drm_fbdev_shmem_defio_fillrect+0x22/0x140 drivers/gpu/drm/drm_fbdev_shmem.c:39
 bit_clear+0x17d/0x220 drivers/video/fbdev/core/bitblit.c:73
 __fbcon_clear+0x633/0x760 drivers/video/fbdev/core/fbcon.c:1358
 fbcon_scroll+0x48b/0x650 drivers/video/fbdev/core/fbcon.c:1910
 con_scroll+0x464/0x690 drivers/tty/vt/vt.c:730
 csi_M drivers/tty/vt/vt.c:2307 [inline]
 csi_ECMA.constprop.0+0x1238/0x3b60 drivers/tty/vt/vt.c:2730
 do_con_trol drivers/tty/vt/vt.c:2945 [inline]
 do_con_write+0x366b/0x4ae0 drivers/tty/vt/vt.c:3442
 con_write+0x23/0xb0 drivers/tty/vt/vt.c:3778
 process_output_block drivers/tty/n_tty.c:557 [inline]
 n_tty_write+0x440/0x1200 drivers/tty/n_tty.c:2366
 iterate_tty_write drivers/tty/tty_io.c:1008 [inline]
 file_tty_write.isra.0+0x4ca/0x8f0 drivers/tty/tty_io.c:1056
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3a15b9fb19
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:00007ffe1abca668 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f3a15e25fa0 RCX: 00007f3a15b9fb19
RDX: 0000000000001006 RSI: 0000200000000680 RDI: 0000000000000006
RBP: 00007f3a15c37b70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3a15e25fac R14: 00007f3a15e25fa0 R15: 00007f3a15e25fa0
 </TASK>

The buggy address belongs to a vmalloc virtual mapping
Memory state around the buggy address:
 ffffc900056fcf00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc900056fcf80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc900056fd000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc900056fd080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc900056fd100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================


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