KASAN: slab-out-of-bounds Read in fbcon_scrolldelta

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e4c26faa Merge tag 'usb-5.9-rc5' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d155f9900000
kernel config: https://syzkaller.appspot.com/x/.config?x=c61610091f4ca8c4
dashboard link: https://syzkaller.appspot.com/bug?extid=9381e25e04a6ea4f2a20
compiler: gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9381e2...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in fbcon_redraw_softback drivers/video/fbdev/core/fbcon.c:1676 [inline]
BUG: KASAN: slab-out-of-bounds in fbcon_scrolldelta+0x10da/0x1230 drivers/video/fbdev/core/fbcon.c:2909
Read of size 2 at addr ffff8881e9ae68c0 by task syz-executor.1/20692

CPU: 0 PID: 20692 Comm: syz-executor.1 Not tainted 5.9.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x198/0x1fd lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
fbcon_redraw_softback drivers/video/fbdev/core/fbcon.c:1676 [inline]
fbcon_scrolldelta+0x10da/0x1230 drivers/video/fbdev/core/fbcon.c:2909
fbcon_set_origin+0x3c/0x50 drivers/video/fbdev/core/fbcon.c:2959
set_origin+0xe7/0x3e0 drivers/tty/vt/vt.c:930
vc_do_resize+0xb0f/0x1150 drivers/tty/vt/vt.c:1305
fbcon_modechanged+0x36c/0x710 drivers/video/fbdev/core/fbcon.c:3011
fbcon_update_vcs+0x3a/0x50 drivers/video/fbdev/core/fbcon.c:3069
do_fb_ioctl+0x62e/0x690 drivers/video/fbdev/core/fbmem.c:1106
fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1181
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5f9
Code: 5d b4 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 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f51ee9c6c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000000e0c0 RCX: 000000000045d5f9
RDX: 0000000020001180 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 000000000118cf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007fffb40f07cf R14: 00007f51ee9c79c0 R15: 000000000118cf4c

Allocated by task 3837:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
kasan_set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
__do_kmalloc mm/slab.c:3655 [inline]
__kmalloc+0x1b0/0x310 mm/slab.c:3664
kmalloc include/linux/slab.h:559 [inline]
kzalloc include/linux/slab.h:666 [inline]
vc_do_resize+0x2f6/0x1150 drivers/tty/vt/vt.c:1228
vt_resizex drivers/tty/vt/vt_ioctl.c:818 [inline]
vt_ioctl+0xef0/0x2cc0 drivers/tty/vt/vt_ioctl.c:1036
tty_ioctl+0x1019/0x15f0 drivers/tty/tty_io.c:2656
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff8881e9ae6000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2240 bytes inside of
4096-byte region [ffff8881e9ae6000, ffff8881e9ae7000)
The buggy address belongs to the page:
page:00000000761e5aa4 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1e9ae6
head:00000000761e5aa4 order:1 compound_mapcount:0
flags: 0x57ffe0000010200(slab|head)
raw: 057ffe0000010200 ffffea0007bbe508 ffffea0007bc1288 ffff8880aa040900
raw: 0000000000000000 ffff8881e9ae6000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881e9ae6780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8881e9ae6800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881e9ae6880: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
^
ffff8881e9ae6900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881e9ae6980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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[Tetsuo Handa]

fbcon_scrolldelta() was removed by commit 50145474f6ef4a9c ("fbcon: remove soft scrollback code").

#syz fix: fbcon: remove soft scrollback code