KASAN: vmalloc-out-of-bounds Write in sys_imageblit

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    6794862a Merge tag 'for-5.5-rc1-kconfig-tag' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17f407f2e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=26dc38a00dc05118a4e6
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+26dc38a00dc05118a4e6@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in fast_imageblit  
drivers/video/fbdev/core/sysimgblt.c:229 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0x117f/0x1240  
drivers/video/fbdev/core/sysimgblt.c:275
Write of size 4 at addr ffffc90008de1000 by task syz-executor.3/19698

CPU: 0 PID: 19698 Comm: syz-executor.3 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS  
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0x5/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:639
 __asan_report_store4_noabort+0x17/0x20 mm/kasan/generic_report.c:139
 fast_imageblit drivers/video/fbdev/core/sysimgblt.c:229 [inline]
 sys_imageblit+0x117f/0x1240 drivers/video/fbdev/core/sysimgblt.c:275
 drm_fb_helper_sys_imageblit+0x21/0x180 drivers/gpu/drm/drm_fb_helper.c:768
 bit_putcs_unaligned drivers/video/fbdev/core/bitblit.c:139 [inline]
 bit_putcs+0x9a3/0xf10 drivers/video/fbdev/core/bitblit.c:188
 fbcon_putcs+0x33c/0x3e0 drivers/video/fbdev/core/fbcon.c:1353
 do_update_region+0x42b/0x6f0 drivers/tty/vt/vt.c:677
 invert_screen+0x2da/0x650 drivers/tty/vt/vt.c:794
 highlight drivers/tty/vt/selection.c:53 [inline]
 clear_selection drivers/tty/vt/selection.c:81 [inline]
 clear_selection+0x59/0x70 drivers/tty/vt/selection.c:77
 vc_do_resize+0x1163/0x1460 drivers/tty/vt/vt.c:1200
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 fbcon_do_set_font+0x4a6/0x960 drivers/video/fbdev/core/fbcon.c:2599
 fbcon_set_font+0x72e/0x860 drivers/video/fbdev/core/fbcon.c:2696
 con_font_set drivers/tty/vt/vt.c:4538 [inline]
 con_font_op+0xe30/0x1270 drivers/tty/vt/vt.c:4603
 vt_ioctl+0xd2e/0x26d0 drivers/tty/vt/vt_ioctl.c:913
 tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a7c9
Code: bd b1 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 8b b1 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fcfa0ba6c88 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000072bf00 RCX: 000000000045a7c9
RDX: 0000000020000140 RSI: 0000000000004b61 RDI: 0000000000000003
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fcfa0ba76d4
R13: 00000000004ab60f R14: 00000000006ede60 R15: 00000000ffffffff


Memory state around the buggy address:
 ffffc90008de0f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90008de0f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffc90008de1000: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
                   ^
 ffffc90008de1080: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
 ffffc90008de1100: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
==================================================================


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