linux-kernel - Re: KASAN: slab-out-of-bounds Read in vc_do

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Date:   Tue, 21 Jan 2020 18:46:09 -0800
From:   syzbot <syzbot+c37a14770d51a085a520@...kaller.appspotmail.com>
To:     daniel.vetter@...ll.ch, ghalat@...hat.com,
        gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-kernel@...r.kernel.org, nico@...xnic.net,
        okash.khawaja@...il.com, oleksandr@...hat.com, sam@...nborg.org,
        syzkaller-bugs@...glegroups.com, textshell@...uujin.de
Subject: Re: KASAN: slab-out-of-bounds Read in vc_do_resize

syzbot has found a reproducer for the following crash on:

HEAD commit:    d96d875e Merge tag 'fixes_for_v5.5-rc8' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13ae7369e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cf8e288883e40aba
dashboard link: https://syzkaller.appspot.com/bug?extid=c37a14770d51a085a520
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16ab6bd1e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c37a14770d51a085a520@...kaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:380 [inline]
BUG: KASAN: slab-out-of-bounds in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: slab-out-of-bounds in vc_do_resize+0x959/0x1460 drivers/tty/vt/vt.c:1250
Read of size 192 at addr ffff8880a3f85940 by task syz-executor.0/9662

CPU: 0 PID: 9662 Comm: syz-executor.0 Not tainted 5.5.0-rc7-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:639
 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:125
 memcpy include/linux/string.h:380 [inline]
 scr_memcpyw include/linux/vt_buffer.h:49 [inline]
 vc_do_resize+0x959/0x1460 drivers/tty/vt/vt.c:1250
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 fbcon_modechanged+0x367/0x790 drivers/video/fbdev/core/fbcon.c:2980
 fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
 fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
 do_fb_ioctl+0x390/0x7d0 drivers/video/fbdev/core/fbmem.c:1104
 fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1180
 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: 0033:0x45b349
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:00007f8865c72c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f8865c736d4 RCX: 000000000045b349
RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000002cd R14: 00000000004c3dc6 R15: 000000000075bf2c

Allocated by task 9662:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc+0x163/0x770 mm/slab.c:3665
 kmalloc include/linux/slab.h:561 [inline]
 kzalloc include/linux/slab.h:670 [inline]
 vc_do_resize+0x262/0x1460 drivers/tty/vt/vt.c:1187
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 fbcon_modechanged+0x367/0x790 drivers/video/fbdev/core/fbcon.c:2980
 fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
 fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
 fbcon_resize+0x6b1/0x780 drivers/video/fbdev/core/fbcon.c:2222
 resize_screen drivers/tty/vt/vt.c:1126 [inline]
 vc_do_resize+0x440/0x1460 drivers/tty/vt/vt.c:1205
 vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
 fbcon_modechanged+0x367/0x790 drivers/video/fbdev/core/fbcon.c:2980
 fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
 fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
 do_fb_ioctl+0x390/0x7d0 drivers/video/fbdev/core/fbmem.c:1104
 fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1180
 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 9469:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:335 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 skb_free_head+0x93/0xb0 net/core/skbuff.c:591
 skb_release_data+0x551/0x8d0 net/core/skbuff.c:611
 skb_release_all+0x4d/0x60 net/core/skbuff.c:665
 __kfree_skb net/core/skbuff.c:679 [inline]
 consume_skb net/core/skbuff.c:838 [inline]
 consume_skb+0xfb/0x410 net/core/skbuff.c:832
 unix_stream_read_generic+0x18ec/0x1de0 net/unix/af_unix.c:2363
 unix_stream_recvmsg+0xc3/0x100 net/unix/af_unix.c:2421
 sock_recvmsg_nosec net/socket.c:873 [inline]
 sock_recvmsg net/socket.c:891 [inline]
 sock_recvmsg+0xce/0x110 net/socket.c:887
 sock_read_iter+0x2f8/0x420 net/socket.c:969
 call_read_iter include/linux/fs.h:1896 [inline]
 new_sync_read+0x680/0x800 fs/read_write.c:414
 __vfs_read+0xe1/0x110 fs/read_write.c:427
 vfs_read+0x1f0/0x440 fs/read_write.c:461
 ksys_read+0x220/0x290 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x73/0xb0 fs/read_write.c:595
 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 ffff8880a3f85800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 320 bytes inside of
 512-byte region [ffff8880a3f85800, ffff8880a3f85a00)
The buggy address belongs to the page:
page:ffffea00028fe140 refcount:1 mapcount:0 mapping:ffff8880aa400a80 index:0x0
raw: 00fffe0000000200 ffffea00029f71c8 ffffea00029463c8 ffff8880aa400a80
raw: 0000000000000000 ffff8880a3f85000 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a3f85880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880a3f85900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880a3f85980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff8880a3f85a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880a3f85a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================