netdev - Re: A slab-out-of-bounds Read bug in __htab_map_lookup_and_delete

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Date:   Thu, 6 Jan 2022 20:02:41 -0800
From:   Yonghong Song <yhs@...com>
To:     butt3rflyh4ck <butterflyhuangxx@...il.com>
CC:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: A slab-out-of-bounds Read bug in
 __htab_map_lookup_and_delete_batch



On 1/6/22 7:25 PM, butt3rflyh4ck wrote:
> Ok, I just reproduce the issue with the latest bpf-next tree.

I cannot reproduce with bpf-next tree. My bpf-next tree top commit is
   70bc793382a0 selftests/bpf: Don't rely on preserving volatile in 
PT_REGS macros in loop3

The config difference between mine and the one you provided.

$ diff .config ~/crash-config
--- .config     2022-01-06 19:29:10.859839241 -0800
+++ /home/yhs/crash-config      2022-01-06 19:27:22.262595087 -0800
@@ -2,16 +2,17 @@
  # Automatically generated file; DO NOT EDIT.
  # Linux/x86 5.16.0-rc7 Kernel Configuration
  #
-CONFIG_CC_VERSION_TEXT="gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-3)"
+CONFIG_CC_VERSION_TEXT="gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0"
  CONFIG_CC_IS_GCC=y
-CONFIG_GCC_VERSION=80500
+CONFIG_GCC_VERSION=90300
  CONFIG_CLANG_VERSION=0
  CONFIG_AS_IS_GNU=y
-CONFIG_AS_VERSION=23000
+CONFIG_AS_VERSION=23400
  CONFIG_LD_IS_BFD=y
-CONFIG_LD_VERSION=23000
+CONFIG_LD_VERSION=23400
  CONFIG_LLD_VERSION=0
  CONFIG_CC_CAN_LINK=y
+CONFIG_CC_CAN_LINK_STATIC=y
  CONFIG_CC_HAS_ASM_GOTO=y
  CONFIG_CC_HAS_ASM_INLINE=y
  CONFIG_CC_HAS_NO_PROFILE_FN_ATTR=y
@@ -117,7 +118,7 @@
  CONFIG_BPF_UNPRIV_DEFAULT_OFF=y
  CONFIG_USERMODE_DRIVER=y
  CONFIG_BPF_PRELOAD=y
-CONFIG_BPF_PRELOAD_UMD=m
+CONFIG_BPF_PRELOAD_UMD=y
  # CONFIG_BPF_LSM is not set
  # end of BPF subsystem

@@ -8456,7 +8457,6 @@
  # CONFIG_DEBUG_INFO_DWARF4 is not set
  # CONFIG_DEBUG_INFO_DWARF5 is not set
  # CONFIG_DEBUG_INFO_BTF is not set
-CONFIG_PAHOLE_HAS_SPLIT_BTF=y
  # CONFIG_GDB_SCRIPTS is not set
  CONFIG_FRAME_WARN=2048
  # CONFIG_STRIP_ASM_SYMS is not set

The main difference is compiler and maybe a couple of other things
which I think should not impact the result.

> On Fri, Jan 7, 2022 at 9:19 AM Yonghong Song <yhs@...com> wrote:
>>
>>
>>
>> On 12/29/21 7:23 PM, butt3rflyh4ck wrote:
>>> Hi, the attachment is a reproducer. Enjoy it.
>>>
>>> Regards,
>>>      butt3rflyh4ck.
>>>
>>>
>>> On Thu, Dec 30, 2021 at 10:23 AM Alexei Starovoitov
>>> <alexei.starovoitov@...il.com> wrote:
>>>>
>>>> On Wed, Dec 29, 2021 at 2:10 AM butt3rflyh4ck
>>>> <butterflyhuangxx@...il.com> wrote:
>>>>>
>>>>> Hi, there is a slab-out-bounds Read bug in
>>>>> __htab_map_lookup_and_delete_batch in kernel/bpf/hashtab.c
>>>>> and I reproduce it in linux-5.16.rc7(upstream) and latest linux-5.15.11.
>>>>>
>>>>> #carsh log
>>>>> [  166.945208][ T6897]
>>>>> ==================================================================
>>>>> [  166.947075][ T6897] BUG: KASAN: slab-out-of-bounds in _copy_to_user+0x87/0xb0
>>>>> [  166.948612][ T6897] Read of size 49 at addr ffff88801913f800 by
>>>>> task __htab_map_look/6897
>>>>> [  166.950406][ T6897]
>>>>> [  166.950890][ T6897] CPU: 1 PID: 6897 Comm: __htab_map_look Not
>>>>> tainted 5.16.0-rc7+ #30
>>>>> [  166.952521][ T6897] Hardware name: QEMU Standard PC (i440FX + PIIX,
>>>>> 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
>>>>> [  166.954562][ T6897] Call Trace:
>>>>> [  166.955268][ T6897]  <TASK>
>>>>> [  166.955918][ T6897]  dump_stack_lvl+0x57/0x7d
>>>>> [  166.956875][ T6897]  print_address_description.constprop.0.cold+0x93/0x347
>>>>> [  166.958411][ T6897]  ? _copy_to_user+0x87/0xb0
>>>>> [  166.959356][ T6897]  ? _copy_to_user+0x87/0xb0
>>>>> [  166.960272][ T6897]  kasan_report.cold+0x83/0xdf
>>>>> [  166.961196][ T6897]  ? _copy_to_user+0x87/0xb0
>>>>> [  166.962053][ T6897]  kasan_check_range+0x13b/0x190
>>>>> [  166.962978][ T6897]  _copy_to_user+0x87/0xb0
>>>>> [  166.964340][ T6897]  __htab_map_lookup_and_delete_batch+0xdc2/0x1590
>>>>> [  166.965619][ T6897]  ? htab_lru_map_update_elem+0xe70/0xe70
>>>>> [  166.966732][ T6897]  bpf_map_do_batch+0x1fa/0x460
>>>>> [  166.967619][ T6897]  __sys_bpf+0x99a/0x3860
>>>>> [  166.968443][ T6897]  ? bpf_link_get_from_fd+0xd0/0xd0
>>>>> [  166.969393][ T6897]  ? rcu_read_lock_sched_held+0x9c/0xd0
>>>>> [  166.970425][ T6897]  ? lock_acquire+0x1ab/0x520
>>>>> [  166.971284][ T6897]  ? find_held_lock+0x2d/0x110
>>>>> [  166.972208][ T6897]  ? rcu_read_lock_sched_held+0x9c/0xd0
>>>>> [  166.973139][ T6897]  ? rcu_read_lock_bh_held+0xb0/0xb0
>>>>> [  166.974096][ T6897]  __x64_sys_bpf+0x70/0xb0
>>>>> [  166.974903][ T6897]  ? syscall_enter_from_user_mode+0x21/0x70
>>>>> [  166.976077][ T6897]  do_syscall_64+0x35/0xb0
>>>>> [  166.976889][ T6897]  entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>> [  166.978027][ T6897] RIP: 0033:0x450f0d
>>>>>
>>>>>
>>>>> In hashtable, if the elements' keys have the same jhash() value, the
>>>>> elements will be put into the same bucket.
>>>>> By putting a lot of elements into a single bucket, the value of
>>>>> bucket_size can be increased to overflow.
>>>>>    but also we can increase bucket_cnt to out of bound Read.

But here bucket_size equals to bucket_cnt (the number of elements in a 
bucket), bucket_cnt has u32 type. The hash table max_entries maximum is
UINT_MAX, so bucket_cnt can at most be UINT_MAX. So I am not sure
how bucket_size/bucket_cnt could overflow. Even if bucket_cnt overflows,
it will wrap as 0 which should not cause issues either.

Maybe I missed something here. Since you can reproduce it, maybe you can 
help debug it a little bit more. It would be even better if you can 
provide a fix. Thanks.

>>
>> I tried the attachment (reproducer) and cannot reproduce the issue
>> with latest bpf-next tree.
>> My config has kasan enabled. Could you send the matching .config file
>> as well so I could reproduce?
>>
>>>>
>>>> Can you be more specific?
>>>> If you can send a patch with a fix it would be even better.
>>>>
>>>>> the out of bound Read in  __htab_map_lookup_and_delete_batch code:
>>>>> ```
>>>>> ...
>>>>> if (bucket_cnt && (copy_to_user(ukeys + total * key_size, keys,
>>>>> key_size * bucket_cnt) ||
>>>>>       copy_to_user(uvalues + total * value_size, values,
>>>>>       value_size * bucket_cnt))) {
>>>>> ret = -EFAULT;
>>>>> goto after_loop;
>>>>> }
>>>>> ...
>>>>> ```
[...]