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Message-ID: <CAFcO6XMyL415YuyhJGP+wyw2xEmtSrtfLzc47+pE-RC88u=8sg@mail.gmail.com>
Date: Fri, 7 Jan 2022 13:42:23 +0800
From: butt3rflyh4ck <butterflyhuangxx@...il.com>
To: Yonghong Song <yhs@...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
Ok, I'll check it out. The call needs CAP_SYS_ADMIN capability, You
can try once again as a root.
Yes, I have debugged it many times. There are multi threads race to
ioctl, it increases debug difficulty.
On Fri, Jan 7, 2022 at 12:02 PM Yonghong Song <yhs@...com> wrote:
>
>
>
> 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;
> >>>>> }
> >>>>> ...
> >>>>> ```
> [...]
--
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