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SubjectKASAN: slab-out-of-bounds Read in fbcon_get_font
From
Hello,

syzbot found the following crash on:

HEAD commit: 76bb8b05 Merge tag 'kbuild-v5.5' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10bfe282e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=dd226651cb0f364b
dashboard link: https://syzkaller.appspot.com/bug?extid=4455ca3b3291de891abc
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11181edae00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=105cbb7ae00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4455ca3b3291de891abc@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:380 [inline]
BUG: KASAN: slab-out-of-bounds in fbcon_get_font+0x2b2/0x5e0
drivers/video/fbdev/core/fbcon.c:2465
Read of size 16 at addr ffff888094b0aa10 by task syz-executor414/9999

CPU: 0 PID: 9999 Comm: syz-executor414 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]
fbcon_get_font+0x2b2/0x5e0 drivers/video/fbdev/core/fbcon.c:2465
con_font_get drivers/tty/vt/vt.c:4446 [inline]
con_font_op+0x20b/0x1250 drivers/tty/vt/vt.c:4605
vt_ioctl+0x181a/0x26d0 drivers/tty/vt/vt_ioctl.c:965
tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2658
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: 0033:0x4444d9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 7b d8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff6f4393b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fff6f4393c0 RCX: 00000000004444d9
RDX: 0000000020000440 RSI: 0000000000004b72 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000400da0
R10: 00007fff6f438f00 R11: 0000000000000246 R12: 00000000004021e0
R13: 0000000000402270 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9999:
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:2658
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 9771:
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
tomoyo_init_log+0x15c1/0x2070 security/tomoyo/audit.c:294
tomoyo_supervisor+0x33f/0xef0 security/tomoyo/common.c:2095
tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
tomoyo_env_perm+0x18e/0x210 security/tomoyo/environ.c:63
tomoyo_environ security/tomoyo/domain.c:670 [inline]
tomoyo_find_next_domain+0x1354/0x1f6c security/tomoyo/domain.c:876
tomoyo_bprm_check_security security/tomoyo/tomoyo.c:107 [inline]
tomoyo_bprm_check_security+0x124/0x1a0 security/tomoyo/tomoyo.c:97
security_bprm_check+0x63/0xb0 security/security.c:784
search_binary_handler+0x71/0x570 fs/exec.c:1645
exec_binprm fs/exec.c:1701 [inline]
__do_execve_file.isra.0+0x1329/0x22b0 fs/exec.c:1821
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 ffff888094b0a000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2576 bytes inside of
4096-byte region [ffff888094b0a000, ffff888094b0b000)
The buggy address belongs to the page:
page:ffffea000252c280 refcount:1 mapcount:0 mapping:ffff8880aa402000
index:0x0 compound_mapcount: 0
raw: 00fffe0000010200 ffffea0002a3ae08 ffffea0002a6aa88 ffff8880aa402000
raw: 0000000000000000 ffff888094b0a000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888094b0a900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888094b0a980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff888094b0aa00: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff888094b0aa80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888094b0ab00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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