KASAN: invalid-free in tcf_exts_destroy

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c2003765 Merge tag 'io_uring-5.6-2020-03-07' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10cd2ae3e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=4527d1e2fb19fd5c
dashboard link: https://syzkaller.appspot.com/bug?extid=dcc34d54d68ef7d2d53d
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1561b01de00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15aad2f9e00000

The bug was bisected to:

commit 599be01ee567b61f4471ee8078870847d0a11e8e
Author: Cong Wang <xiyou.w...@gmail.com>
Date: Mon Feb 3 05:14:35 2020 +0000

net_sched: fix an OOB access in cls_tcindex

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10a275fde00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=12a275fde00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14a275fde00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+dcc34d...@syzkaller.appspotmail.com
Fixes: 599be01ee567 ("net_sched: fix an OOB access in cls_tcindex")

IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: double-free or invalid-free in tcf_exts_destroy+0x62/0xc0 net/sched/cls_api.c:3002

CPU: 1 PID: 9507 Comm: syz-executor467 Not tainted 5.6.0-rc4-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+0x188/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:374
kasan_report_invalid_free+0x61/0xa0 mm/kasan/report.c:468
__kasan_slab_free+0x129/0x140 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x109/0x2b0 mm/slab.c:3757
tcf_exts_destroy+0x62/0xc0 net/sched/cls_api.c:3002
tcf_exts_change+0xf4/0x150 net/sched/cls_api.c:3059
tcindex_set_parms+0xed8/0x1a00 net/sched/cls_tcindex.c:456
tcindex_change+0x203/0x2e0 net/sched/cls_tcindex.c:518
tc_new_tfilter+0xa59/0x20b0 net/sched/cls_api.c:2103
rtnetlink_rcv_msg+0x810/0xad0 net/core/rtnetlink.c:5427
netlink_rcv_skb+0x15a/0x410 net/netlink/af_netlink.c:2478
netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
____sys_sendmsg+0x6b9/0x7d0 net/socket.c:2343
___sys_sendmsg+0x100/0x170 net/socket.c:2397
__sys_sendmsg+0xec/0x1b0 net/socket.c:2430
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x270/0xe8f arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Allocated by task 1:
save_stack+0x1b/0x80 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:515 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:488
kmem_cache_alloc_trace+0x153/0x7d0 mm/slab.c:3551
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
__class_register+0x46/0x450 drivers/base/class.c:160
spi_transport_init+0xf0/0x132 drivers/scsi/scsi_transport_spi.c:1609
do_one_initcall+0x10a/0x7d0 init/main.c:1152
do_initcall_level init/main.c:1225 [inline]
do_initcalls init/main.c:1241 [inline]
do_basic_setup init/main.c:1261 [inline]
kernel_init_freeable+0x501/0x5ae init/main.c:1445
kernel_init+0xd/0x1bb init/main.c:1352
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8880a12d5000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 152 bytes inside of
1024-byte region [ffff8880a12d5000, ffff8880a12d5400)
The buggy address belongs to the page:
page:ffffea000284b540 refcount:1 mapcount:0 mapping:ffff8880aa000c40 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea000285c288 ffffea000284b588 ffff8880aa000c40
raw: 0000000000000000 ffff8880a12d5000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a12d4f80: 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a12d5000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880a12d5080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
^
ffff8880a12d5100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8880a12d5180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Cong Wang]

Looks like a consequence of "slab-out-of-bounds Write in tcindex_set_parms".

Thanks.

[Eric Dumazet]

I have a dozen more syzbot reports involving net/sched code, do you want
me to release them right now ?

[Cong Wang]

I have no problem with this, at least I can close them as dup etc.. Please
go ahead.

Thanks.

[Cong Wang]

#syz test: https://github.com/congwang/linux.git tcindex

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger crash:

Reported-and-tested-by: syzbot+dcc34d...@syzkaller.appspotmail.com

Tested on:

commit: 2c19e526 net_sched: hold rtnl lock for tcindex_partial_des..
git tree: https://github.com/congwang/linux.git tcindex
kernel config: https://syzkaller.appspot.com/x/.config?x=bcbe864577669742

dashboard link: https://syzkaller.appspot.com/bug?extid=dcc34d54d68ef7d2d53d
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386

Note: testing is done by a robot and is best-effort only.