KASAN: use-after-free Read in vc_do

KASAN: use-after-free Read in vc_do_resize
Status: upstream: reported on 2020/05/11 06:21
Reported-by: syzbot+3c9716daab4ea34d814f@syzkaller.appspotmail.com
First crash: 23d, last: 9d21h

Sample crash report:

==================================================================
BUG: KASAN: use-after-free in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
BUG: KASAN: use-after-free in vc_do_resize+0xe3e/0x1ce0 drivers/tty/vt/vt.c:1280
Read of size 2 at addr ffff8880959959c0 by task syz-executor.0/14676

CPU: 0 PID: 14676 Comm: syz-executor.0 Not tainted 5.7.0-rc6-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+0x1e9/0x30e lib/dump_stack.c:118
 print_address_description+0x74/0x5c0 mm/kasan/report.c:382
 __kasan_report+0x103/0x1a0 mm/kasan/report.c:511
 kasan_report+0x4d/0x80 mm/kasan/common.c:625

Allocated by task 7219:
 save_stack mm/kasan/common.c:49 [inline]
 set_track mm/kasan/common.c:57 [inline]
 __kasan_kmalloc+0x114/0x160 mm/kasan/common.c:495
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc+0x24b/0x330 mm/slab.c:3665
 kmalloc_array include/linux/slab.h:597 [inline]
 kcalloc+0x2b/0x50 include/linux/slab.h:608
 ext4_find_extent+0x2cb/0xcf0 fs/ext4/extents.c:860
 ext4_ext_map_blocks+0x13e/0x6db0 fs/ext4/extents.c:4039
 ext4_map_blocks+0x43b/0x1b00 fs/ext4/inode.c:544
 ext4_getblk+0xa4/0x460 fs/ext4/inode.c:825
 ext4_bread+0x48/0x330 fs/ext4/inode.c:875
 ext4_append+0x153/0x2d0 fs/ext4/namei.c:67
 ext4_init_new_dir fs/ext4/namei.c:2755 [inline]
 ext4_mkdir+0x756/0x1460 fs/ext4/namei.c:2800
 vfs_mkdir+0x42a/0x620 fs/namei.c:3625
 do_mkdirat+0x1b9/0x310 fs/namei.c:3648
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3

Freed by task 7219:
 save_stack mm/kasan/common.c:49 [inline]
 set_track mm/kasan/common.c:57 [inline]
 kasan_set_free_info mm/kasan/common.c:317 [inline]
 __kasan_slab_free+0x125/0x190 mm/kasan/common.c:456
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x220 mm/slab.c:3757
 ext4_ext_map_blocks+0x421f/0x6db0 fs/ext4/extents.c:4319
 ext4_map_blocks+0x43b/0x1b00 fs/ext4/inode.c:544
 ext4_getblk+0xa4/0x460 fs/ext4/inode.c:825
 ext4_bread+0x48/0x330 fs/ext4/inode.c:875
 ext4_append+0x153/0x2d0 fs/ext4/namei.c:67
 ext4_init_new_dir fs/ext4/namei.c:2755 [inline]
 ext4_mkdir+0x756/0x1460 fs/ext4/namei.c:2800
 vfs_mkdir+0x42a/0x620 fs/namei.c:3625
 do_mkdirat+0x1b9/0x310 fs/namei.c:3648
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3

The buggy address belongs to the object at ffff888095995980
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 64 bytes inside of
 96-byte region [ffff888095995980, ffff8880959959e0)
The buggy address belongs to the page:
page:ffffea0002566540 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888095995200
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea000238b9c8 ffffea00024f9b48 ffff8880aa400540
raw: ffff888095995200 ffff888095995000 0000000100000017 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888095995880: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
 ffff888095995900: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
>ffff888095995980: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                                           ^
 ffff888095995a00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff888095995a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
==================================================================

Crashes (3):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Maintainers
ci-upstream-kasan-gce-smack-root	2020/05/24 07:24	upstream	423b8baf	96c92ad3	.config	log	report	daniel.vetter@ffwll.ch, gregkh@linuxfoundation.org, jslaby@suse.com, linux-kernel@vger.kernel.org, nico@fluxnic.net, sam@ravnborg.org
ci-upstream-linux-next-kasan-gce-root	2020/05/21 02:19	linux-next	ac935d22	c61086ab	.config	log	report	daniel.vetter@ffwll.ch, gregkh@linuxfoundation.org, jslaby@suse.com, linux-kernel@vger.kernel.org, nico@fluxnic.net, sam@ravnborg.org
ci-upstream-linux-next-kasan-gce-root	2020/05/11 01:31	linux-next	ac935d22	8742a2b9	.config	log	report	daniel.vetter@ffwll.ch, gregkh@linuxfoundation.org, jslaby@suse.com, linux-kernel@vger.kernel.org, nico@fluxnic.net, sam@ravnborg.org