Re: KASAN: use-after-free Read in vc_do_resize

From: syzbot
Date: Mon Aug 03 2020 - 09:55:26 EST

syzbot has found a reproducer for the following issue on:

HEAD commit: bcf87687 Linux 5.8
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1268f642900000
kernel config: https://syzkaller.appspot.com/x/.config?x=19b11af1e394136d
dashboard link: https://syzkaller.appspot.com/bug?extid=3c9716daab4ea34d814f
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16f48ecc900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15dd8c78900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3c9716daab4ea34d814f@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in memcpy include/linux/string.h:406 [inline]
BUG: KASAN: use-after-free in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: use-after-free in vc_do_resize+0x9d6/0x13f0 drivers/tty/vt/vt.c:1286
Read of size 2 at addr ffff88809da9f8c2 by task syz-executor887/23625

CPU: 1 PID: 23625 Comm: syz-executor887 Not tainted 5.8.0-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+0x18f/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
check_memory_region_inline mm/kasan/generic.c:186 [inline]
check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
memcpy+0x20/0x60 mm/kasan/common.c:105
memcpy include/linux/string.h:406 [inline]
scr_memcpyw include/linux/vt_buffer.h:49 [inline]
vc_do_resize+0x9d6/0x13f0 drivers/tty/vt/vt.c:1286
fbcon_modechanged+0x36c/0x710 drivers/video/fbdev/core/fbcon.c:2990
fbcon_update_vcs+0x3a/0x50 drivers/video/fbdev/core/fbcon.c:3048
fb_set_var+0xae8/0xd60 drivers/video/fbdev/core/fbmem.c:1056
do_fb_ioctl+0x33f/0x6c0 drivers/video/fbdev/core/fbmem.c:1109
fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1185
vfs_ioctl fs/ioctl.c:48 [inline]
ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
__do_sys_ioctl fs/ioctl.c:762 [inline]
__se_sys_ioctl fs/ioctl.c:760 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x44aa19
Code: e8 3c e6 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 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 2b 06 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f027d75bdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006e69f8 RCX: 000000000044aa19
RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00000000006e69f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e69fc
R13: 00007ffcf24f523f R14: 00007f027d75c9c0 R15: 20c49ba5e353f7cf

Allocated by task 23115:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
kmem_cache_alloc_trace+0x14f/0x2d0 mm/slab.c:3551
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
apparmor_sk_alloc_security+0x79/0xf0 security/apparmor/lsm.c:776
security_sk_alloc+0x50/0xb0 security/security.c:2180
sk_prot_alloc+0xae/0x300 net/core/sock.c:1696
sk_alloc+0x32/0xbd0 net/core/sock.c:1747
unix_create1+0xbf/0x730 net/unix/af_unix.c:795
unix_create+0xf9/0x1e0 net/unix/af_unix.c:857
__sock_create+0x3ca/0x740 net/socket.c:1428
sock_create net/socket.c:1479 [inline]
__sys_socketpair+0x242/0x570 net/socket.c:1583
__do_sys_socketpair net/socket.c:1632 [inline]
__se_sys_socketpair net/socket.c:1629 [inline]
__x64_sys_socketpair+0x93/0xf0 net/socket.c:1629
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 23107:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
kasan_set_free_info mm/kasan/common.c:316 [inline]
__kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x103/0x2c0 mm/slab.c:3757
security_sk_free+0x3e/0x70 security/security.c:2185
sk_prot_free net/core/sock.c:1726 [inline]
__sk_destruct+0x537/0x860 net/core/sock.c:1815
sk_destruct+0xbd/0xe0 net/core/sock.c:1830
__sk_free+0xef/0x3d0 net/core/sock.c:1841
sk_free+0x78/0xa0 net/core/sock.c:1852
sock_put include/net/sock.h:1781 [inline]
unix_release_sock+0x7fc/0xc10 net/unix/af_unix.c:574
unix_release+0x3f/0x80 net/unix/af_unix.c:867
__sock_release+0xcd/0x280 net/socket.c:605
sock_close+0x18/0x20 net/socket.c:1278
__fput+0x33c/0x880 fs/file_table.c:281
task_work_run+0xdd/0x190 kernel/task_work.c:135
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop arch/x86/entry/common.c:239 [inline]
__prepare_exit_to_usermode+0x1e9/0x1f0 arch/x86/entry/common.c:269
do_syscall_64+0x6c/0xe0 arch/x86/entry/common.c:393
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff88809da9f8c0
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 2 bytes inside of
32-byte region [ffff88809da9f8c0, ffff88809da9f8e0)
The buggy address belongs to the page:
page:ffffea000276a7c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88809da9ffc1
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002789fc8 ffffea0002a46148 ffff8880aa0001c0
raw: ffff88809da9ffc1 ffff88809da9f000 000000010000003c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809da9f780: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
ffff88809da9f800: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff88809da9f880: 00 02 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
^
ffff88809da9f900: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
ffff88809da9f980: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================