BUG: bad usercopy in old_dev_ioctl

[syzbot]

Hello,

syzkaller hit the following crash on
6084b576dca2e898f5c101baef151f7bfdbb606d
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.

Unfortunately, I don't have any reproducer for this bug yet.


device gre0 entered promiscuous mode
usercopy: kernel memory exposure attempt detected from 00000000a6830059
(kmalloc-1024) (1024 bytes)
------------[ cut here ]------------
kernel BUG at mm/usercopy.c:84!
invalid opcode: 0000 [#1] SMP
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 28799 Comm: syz-executor4 Not tainted 4.15.0-rc3-next-20171214+
#67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:report_usercopy mm/usercopy.c:76 [inline]
RIP: 0010:__check_object_size+0x1e2/0x250 mm/usercopy.c:276
RSP: 0018:ffffc9000116fc50 EFLAGS: 00010286
RAX: 0000000000000063 RBX: ffffffff82e6518f RCX: ffffffff8123dede
RDX: 0000000000004c58 RSI: ffffc900050ed000 RDI: ffff88021fd136f8
RBP: ffffc9000116fc88 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880216bb6050
R13: 0000000000000400 R14: 0000000000000001 R15: ffffffff82eda864
FS: 00007f61a06bc700(0000) GS:ffff88021fd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020a5afd8 CR3: 000000020f8a9000 CR4: 00000000001406e0
Call Trace:
check_object_size include/linux/thread_info.h:112 [inline]
check_copy_size include/linux/thread_info.h:143 [inline]
copy_to_user include/linux/uaccess.h:154 [inline]
old_dev_ioctl.isra.1+0x21d/0x9a0 net/bridge/br_ioctl.c:178
br_dev_ioctl+0x3f/0xa0 net/bridge/br_ioctl.c:392
dev_ifsioc+0x175/0x520 net/core/dev_ioctl.c:354
dev_ioctl+0x548/0x7a0 net/core/dev_ioctl.c:589
sock_ioctl+0x150/0x320 net/socket.c:998
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0xaf/0x840 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452a39
RSP: 002b:00007f61a06bbc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f61a06bc700 RCX: 0000000000452a39
RDX: 0000000020a59fd8 RSI: 00000000000089f0 RDI: 0000000000000014
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
R13: 0000000000a6f7ff R14: 00007f61a06bc9c0 R15: 0000000000000000
Code: 7b e5 82 48 0f 44 da e8 8d 82 eb ff 48 8b 45 d0 4d 89 e9 4c 89 e1 4c
89 fa 48 89 de 48 c7 c7 a8 51 e6 82 49 89 c0 e8 76 b7 e3 ff <0f> 0b 48 c7
c0 43 51 e6 82 eb a1 48 c7 c0 53 51 e6 82 eb 98 48
RIP: report_usercopy mm/usercopy.c:76 [inline] RSP: ffffc9000116fc50
RIP: __check_object_size+0x1e2/0x250 mm/usercopy.c:276 RSP: ffffc9000116fc50
---[ end trace 5fadb883cda020dc ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Kees Cook]

On Sat, Dec 16, 2017 at 11:47 PM, syzbot
<bot+5e56fb40e0f2bc3f20...@syzkaller.appspotmail.com>
wrote:

Uhh, this doesn't make sense, much like the other report...

indices = kcalloc(num, sizeof(int), GFP_KERNEL);
if (indices == NULL)
return -ENOMEM;

get_port_ifindices(br, indices, num);
if (copy_to_user((void __user *)args[1], indices,
num*sizeof(int)))

offset is 0. size overlaps. usercopy checks in -next must be broken. I
will double-check.

-Kees

--
Kees Cook
Pixel Security

[Dmitry Vyukov]

Start of heap object ending at 0x59 looks bogus, right?

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[Kees Cook]

No, that's a hashed address. %p doesn't report real addresses any more.

-Kees

[Dmitry Vyukov]

Ah, for some reason I thought that 64-bit hashing just strips upper
part (because what would be a reason to strip it from a hash? and
showing lower bytes is useful and does not reveal too much).

[Dmitry Vyukov]

Bad things on kmalloc-1024 are most likely caused by an invalid free
in pcrypt, it freed a pointer into a middle of a 1024 byte heap object
which was undetected by KASAN (now there is a patch for this in mm
tree) and later caused all kinds of bad things:
https://groups.google.com/forum/#!topic/syzkaller-bugs/NKn_ivoPOpk
https://patchwork.kernel.org/patch/10126761/

#syz dup: KASAN: use-after-free Read in __list_del_entry_valid (2)