KASAN: use-after-free Read in soft

KASAN: use-after-free Read in soft_cursor
Status: upstream: reported C repro on 2019/12/06 12:25
Reported-by: syzbot+cf43fb300aa142fb024b@syzkaller.appspotmail.com
First crash: 77d, last: 20h22m

Cause bisection: introduced by (bisect log):

commit 2de50e9674fc4ca3c6174b04477f69eb26b4ee31
Author: Russell Currey <ruscur@russell.cc>
Date: Mon Feb 8 04:08:20 2016 +0000

powerpc/powernv: Remove support for p5ioc2

Crash: BUG: spinlock lockup suspected in nf_conntrack_lock (log)
Repro: C syz .config

similar bugs (2):
Kernel	Title	Repro	Bisected	Count	Last	Reported	Patched	Status
linux-4.19	KASAN: use-after-free Read in soft_cursor	C		6	25d	79d	0/1	upstream: reported C repro on 2019/12/04 13:15
linux-4.14	KASAN: use-after-free Read in soft_cursor	C		2	10d	79d	0/1	upstream: reported C repro on 2019/12/04 13:11

Sample crash report:

==================================================================
BUG: KASAN: use-after-free in memcpy include/linux/string.h:380 [inline]
BUG: KASAN: use-after-free in soft_cursor+0x439/0xa30 drivers/video/fbdev/core/softcursor.c:70
Read of size 9 at addr ffff88809826c851 by task syz-executor602/9482

CPU: 1 PID: 9482 Comm: syz-executor602 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: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]
 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: 0033:0x440219
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 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff7d7f09e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440219
RDX: 00000000200002c0 RSI: 000000000000560a RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000001 R09: 00000000004002c8
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000401b00
R13: 0000000000401b90 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9477:
 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_node mm/slab.c:3616 [inline]
 __kmalloc_node_track_caller+0x4e/0x70 mm/slab.c:3630
 __kmalloc_reserve.isra.0+0x40/0xf0 net/core/skbuff.c:141
 __alloc_skb+0x10b/0x5e0 net/core/skbuff.c:209
 alloc_skb include/linux/skbuff.h:1049 [inline]
 sock_wmalloc+0xd9/0x120 net/core/sock.c:2093
 unix_stream_connect+0x22a/0x146b net/unix/af_unix.c:1249
 __sys_connect_file+0x25d/0x2e0 net/socket.c:1848
 __sys_connect+0x51/0x90 net/socket.c:1861
 __do_sys_connect net/socket.c:1872 [inline]
 __se_sys_connect net/socket.c:1869 [inline]
 __x64_sys_connect+0x73/0xb0 net/socket.c:1869
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9477:
 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]
 kfree_skb net/core/skbuff.c:697 [inline]
 kfree_skb+0x101/0x420 net/core/skbuff.c:691
 unix_stream_connect+0x1342/0x146b net/unix/af_unix.c:1391
 __sys_connect_file+0x25d/0x2e0 net/socket.c:1848
 __sys_connect+0x51/0x90 net/socket.c:1861
 __do_sys_connect net/socket.c:1872 [inline]
 __se_sys_connect net/socket.c:1869 [inline]
 __x64_sys_connect+0x73/0xb0 net/socket.c:1869
 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 ffff88809826c800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 81 bytes inside of
 512-byte region [ffff88809826c800, ffff88809826ca00)
The buggy address belongs to the page:
page:ffffea0002609b00 refcount:1 mapcount:0 mapping:ffff8880aa400a80 index:0xffff88809826c000
raw: 00fffe0000000200 ffffea00029e84c8 ffffea0002594288 ffff8880aa400a80
raw: ffff88809826c000 ffff88809826c000 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809826c700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809826c780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88809826c800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88809826c880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809826c900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Fix bisection attempts:
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro
ci-upstream-kasan-gce-selinux-root	2020/01/26 21:41	upstream	5cf9ad0e	98b4ef2d	.config	log	report	syz	C

Crashes (6):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	Maintainers
ci-upstream-kasan-gce-selinux-root	2019/12/06 11:48	upstream	b0d4beaa	98b4ef2d	.config	log	report	syz	C	b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
ci-upstream-kasan-gce-root	2019/12/06 11:06	upstream	b0d4beaa	98b4ef2d	.config	log	report	syz	C	b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
ci-upstream-linux-next-kasan-gce-root	2019/12/18 13:06	linux-next	b9c5ef25	f2fe0772	.config	log	report	syz	C	b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
ci-upstream-kasan-gce-selinux-root	2019/12/18 23:40	upstream	2187f215	79b211f7	.config	log	report			b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
ci-qemu-upstream-386	2019/12/21 17:39	upstream	62104694	bc586918	.config	log	report			b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org
ci-upstream-linux-next-kasan-gce-root	2020/02/21 04:53	linux-next	bee46b30	bd2a74a3	.config	log	report			b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org