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

Wed May 28 09:22:32 UTC 2025

Hello,

syzbot found the following issue on:

HEAD commit:    a5806cd506af Linux 6.15-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12afde70580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=87b7b87abbf1a67f
dashboard link: https://syzkaller.appspot.com/bug?extid=7a63ce155648954e749b
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d0398ca67d9a/disk-a5806cd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dccdb3c5ff14/vmlinux-a5806cd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3d94cf3493b5/bzImage-a5806cd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7a63ce155648954e749b at 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:134 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_fillrect_static drivers/video/fbdev/core/fb_fillrect.h:220 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_fillrect drivers/video/fbdev/core/fb_fillrect.h:279 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_fillrect+0x15d4/0x17b0 drivers/video/fbdev/core/sysfillrect.c:22
Write of size 8 at addr ffffc90003849000 by task syz.1.1552/13525

CPU: 1 UID: 0 PID: 13525 Comm: syz.1.1552 Tainted: G     U              6.15.0-rc7-syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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+0xe0/0x110 mm/kasan/report.c:634
 fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
 bitfill drivers/video/fbdev/core/fb_fillrect.h:134 [inline]
 fb_fillrect_static drivers/video/fbdev/core/fb_fillrect.h:220 [inline]
 fb_fillrect drivers/video/fbdev/core/fb_fillrect.h:279 [inline]
 sys_fillrect+0x15d4/0x17b0 drivers/video/fbdev/core/sysfillrect.c:22
 drm_fbdev_shmem_defio_fillrect+0x22/0x140 drivers/gpu/drm/drm_fbdev_shmem.c:37
 bit_clear+0x17a/0x220 drivers/video/fbdev/core/bitblit.c:73
 __fbcon_clear+0x600/0x780 drivers/video/fbdev/core/fbcon.c:1292
 fbcon_scroll+0x48b/0x690 drivers/video/fbdev/core/fbcon.c:1851
 con_scroll+0x45c/0x690 drivers/tty/vt/vt.c:579
 csi_M drivers/tty/vt/vt.c:2072 [inline]
 csi_ECMA drivers/tty/vt/vt.c:2483 [inline]
 do_con_trol drivers/tty/vt/vt.c:2657 [inline]
 do_con_write+0x6869/0x7c90 drivers/tty/vt/vt.c:3092
 con_write+0x23/0xb0 drivers/tty/vt/vt.c:3432
 process_output_block drivers/tty/n_tty.c:561 [inline]
 n_tty_write+0x40f/0x1160 drivers/tty/n_tty.c:2377
 iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
 file_tty_write.constprop.0+0x502/0x9b0 drivers/tty/tty_io.c:1090
 tty_write drivers/tty/tty_io.c:1111 [inline]
 redirected_tty_write drivers/tty/tty_io.c:1134 [inline]
 redirected_tty_write+0xd4/0x150 drivers/tty/tty_io.c:1114
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x5ba/0x1180 fs/read_write.c:684
 ksys_write+0x12a/0x240 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f457158e969
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:00007f457244f038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f45717b5fa0 RCX: 00007f457158e969
RDX: 0000000000000013 RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007f4571610ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f45717b5fa0 R15: 00007ffddb9e8a38
 </TASK>

The buggy address ffffc90003849000 belongs to a vmalloc virtual mapping
Memory state around the buggy address:
 ffffc90003848f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003848f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90003849000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc90003849080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003849100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================

---
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