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

From: syzbot
Date: Wed Dec 04 2019 - 11:32:10 EST

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Hello,

syzbot found the following crash on:

HEAD commit: 63de3747 Merge tag 'tag-chrome-platform-for-v5.5' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14819aeae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=1d189d07c6717979
dashboard link: https://syzkaller.appspot.com/bug?extid=16469b5e8e5a72e9131e
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+16469b5e8e5a72e9131e@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:380 [inline]
BUG: KASAN: slab-out-of-bounds in soft_cursor+0x439/0xa30 drivers/video/fbdev/core/softcursor.c:70
Read of size 9 at addr ffff888094efeaf2 by task syz-executor.2/30416

CPU: 0 PID: 30416 Comm: syz-executor.2 Not tainted 5.4.0-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+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:638
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
memcpy+0x24/0x50 mm/kasan/common.c:124
memcpy include/linux/string.h:380 [inline]
soft_cursor+0x439/0xa30 drivers/video/fbdev/core/softcursor.c:70
bit_cursor+0x12fc/0x1a60 drivers/video/fbdev/core/bitblit.c:386
fbcon_cursor+0x487/0x660 drivers/video/fbdev/core/fbcon.c:1402
hide_cursor+0x9d/0x2b0 drivers/tty/vt/vt.c:895
redraw_screen+0x60b/0x7d0 drivers/tty/vt/vt.c:988
vc_do_resize+0x10c9/0x1460 drivers/tty/vt/vt.c:1284
vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
vt_ioctl+0x2076/0x26d0 drivers/tty/vt/vt_ioctl.c:887
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: 0033:0x45a679
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f25945c0c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a679
RDX: 00000000200002c0 RSI: 000000000000560a RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f25945c16d4
R13: 00000000004c6ce2 R14: 00000000004dd2d0 R15: 00000000ffffffff

Allocated by task 18150:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:512 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:485
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:526
__do_kmalloc mm/slab.c:3656 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3665
kmalloc include/linux/slab.h:561 [inline]
fbcon_set_font+0x32d/0x860 drivers/video/fbdev/core/fbcon.c:2663
con_font_set drivers/tty/vt/vt.c:4538 [inline]
con_font_op+0xe18/0x1250 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

Freed by task 17018:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
kasan_set_free_info mm/kasan/common.c:334 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:473
kasan_slab_free+0xe/0x10 mm/kasan/common.c:482
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
free_bprm+0x198/0x200 fs/exec.c:1433
__do_execve_file.isra.0+0x1abd/0x22b0 fs/exec.c:1831
do_execveat_common fs/exec.c:1867 [inline]
do_execve fs/exec.c:1884 [inline]
__do_sys_execve fs/exec.c:1960 [inline]
__se_sys_execve fs/exec.c:1955 [inline]
__x64_sys_execve+0x8f/0xc0 fs/exec.c:1955
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888094efe800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 242 bytes to the right of
512-byte region [ffff888094efe800, ffff888094efea00)
The buggy address belongs to the page:
page:ffffea000253bf80 refcount:1 mapcount:0 mapping:ffff8880aa400a80 index:0xffff888094efe400
raw: 00fffe0000000200 ffffea0002634fc8 ffffea000287f088 ffff8880aa400a80
raw: ffff888094efe400 ffff888094efe000 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888094efe980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888094efea00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

ffff888094efea80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

^
ffff888094efeb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888094efeb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

---
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Next message: Steven Price: "Re: [PATCH v15 00/23] Generic page walk and ptdump"
Previous message: Daniel Lezcano: "Re: [PATCH v2 00/11] thermal: clean up output of make W=1"
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