Re: Out-of-bounds access in __do_proc_doulongvec_minmax

From: Andrey Ryabinin
Date: Wed Dec 03 2014 - 08:37:48 EST

On 12/03/2014 04:27 PM, Dmitry Vyukov wrote:
> On Wed, Dec 3, 2014 at 3:39 PM, Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> wrote:
>> On 12/03/2014 12:04 PM, Dmitry Vyukov wrote:
>>> Hi,
>>>
>>> I am working on AddressSanitizer, a fast memory error detector for kernel:
>>> https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
>>>
>>> Here is a bug report that I've got while running trinity:
>>>
>>> ==================================================================
>>> BUG: AddressSanitizer: out of bounds access in
>>> __do_proc_doulongvec_minmax+0x8a0/0x9a0 at addr ffffffff83980960
>>> Read of size 8 by task trinity-c14/6919
>>> Out-of-bounds access to the global variable 'zero'
>>> [ffffffff83980960-ffffffff83980964) defined at ipc/ipc_sysctl.c:158
>>
>> This line seems incorrect. Judging from the backtrace below variable 'zero' is
>> defined in kernel/sysctl.c:123
>>
>>
>>>
>>> CPU: 1 PID: 6919 Comm: trinity-c14 Not tainted 3.18.0-rc1+ #50
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>> 0000000000000001 ffff8800b68cf418 ffffffff82c2d3ae 0000000000000000
>>> ffff8800b68cf4c0 ffff8800b68cf4a8 ffffffff813eaa81 ffffffff0000000c
>>> ffff88010b003600 ffff8800b68cf479 0000000000000296 0000000000000000
>>> Call Trace:
>>> [<ffffffff813ead71>] __asan_report_load8_noabort+0x51/0x70
>>> mm/kasan/report.c:248
>>> [<ffffffff810cc3e0>] __do_proc_doulongvec_minmax+0x8a0/0x9a0
>>> kernel/sysctl.c:2284
>>> [< inlined >] proc_doulongvec_minmax+0x50/0x80
>>> do_proc_doulongvec_minmax kernel/sysctl.c:2322
>>> [<ffffffff810cc530>] proc_doulongvec_minmax+0x50/0x80 kernel/sysctl.c:2345
>>> [<ffffffff813c9e5a>] hugetlb_sysctl_handler_common+0x12a/0x3c0
>>> mm/hugetlb.c:2270
>>> [<ffffffff813cb45c>] hugetlb_mempolicy_sysctl_handler+0x1c/0x20
>>> mm/hugetlb.c:2293
>>> [<ffffffff8153e6e9>] proc_sys_call_handler+0x179/0x1f0
>>> fs/proc/proc_sysctl.c:506
>>> [<ffffffff8153e76f>] proc_sys_write+0xf/0x20 fs/proc/proc_sysctl.c:524
>>> [<ffffffff813f1563>] __kernel_write+0x123/0x440 fs/read_write.c:502
>>> [<ffffffff8147ebaa>] write_pipe_buf+0x14a/0x1d0 fs/splice.c:1074
>>> [< inlined >] __splice_from_pipe+0x22e/0x6f0
>>> splice_from_pipe_feed fs/splice.c:769
>>> [<ffffffff8147dbde>] __splice_from_pipe+0x22e/0x6f0 fs/splice.c:886
>>> [<ffffffff81483211>] splice_from_pipe+0xc1/0x110 fs/splice.c:921
>>> [<ffffffff81483298>] default_file_splice_write+0x18/0x50 fs/splice.c:1086
>>> [< inlined >] direct_splice_actor+0x104/0x1c0 do_splice_from
>>> fs/splice.c:1128
>>> [<ffffffff8147cfc4>] direct_splice_actor+0x104/0x1c0 fs/splice.c:1284
>>> [<ffffffff8147e5ba>] splice_direct_to_actor+0x24a/0x6f0 fs/splice.c:1237
>>> [<ffffffff81483424>] do_splice_direct+0x154/0x270 fs/splice.c:1327
>>> [<ffffffff813f3bfb>] do_sendfile+0x5fb/0x1260 fs/read_write.c:1266
>>> [< inlined >] SyS_sendfile64+0xfa/0x100 SYSC_sendfile64
>>> fs/read_write.c:1327
>>> [<ffffffff813f6bea>] SyS_sendfile64+0xfa/0x100 fs/read_write.c:1313
>>> [<ffffffff82c464f9>] ia32_do_call+0x13/0x13 arch/x86/ia32/ia32entry.S:444
>>> Memory state around the buggy address:
>>> ffffffff83980680: 04 f8 f8 f8 f8 f8 f8 f8 02 f8 f8 f8 f8 f8 f8 f8
>>> ffffffff83980700: 00 f8 f8 f8 f8 f8 f8 f8 00 f8 f8 f8 f8 f8 f8 f8
>>> ffffffff83980780: 00 00 00 00 00 00 00 00 f8 f8 f8 f8 00 00 00 00
>>> ffffffff83980800: 00 00 00 00 00 00 00 00 f8 f8 f8 f8 04 f8 f8 f8
>>> ffffffff83980880: f8 f8 f8 f8 04 f8 f8 f8 f8 f8 f8 f8 04 f8 f8 f8
>>>> ffffffff83980900: f8 f8 f8 f8 04 f8 f8 f8 f8 f8 f8 f8 04 f8 f8 f8
>>> ^
>>> ffffffff83980980: f8 f8 f8 f8 00 00 00 00 f8 f8 f8 f8 00 00 00 00
>>> ffffffff83980a00: 02 f8 f8 f8 f8 f8 f8 f8 00 00 00 00 00 00 00 00
>>> ffffffff83980a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>> ffffffff83980b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>> ffffffff83980b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>> ==================================================================
>>>
>>> The core creates ctl_table as:
>>>
>>> static int zero;
>>> static int one = 1;
>>> static int int_max = INT_MAX;
>>> static struct ctl_table ipc_kern_table[] = {
>>> {
>>> ...
>>> {
>>> .procname = "shm_rmid_forced",
>>> .data = &init_ipc_ns.shm_rmid_forced,
>>> .maxlen = sizeof(init_ipc_ns.shm_rmid_forced),
>>> .mode = 0644,
>>> .proc_handler = proc_ipc_dointvec_minmax_orphans,
>>> .extra1 = &zero,
>>> .extra2 = &one,
>>> },
>>>
>>> But later extra1/2 are casted to *unsigned long**:
>>>
>>> static int __do_proc_doulongvec_minmax(void *data, struct ctl_table
>>> *table, int write, ...
>>> {
>>> ...
>>> min = (unsigned long *) table->extra1;
>>> max = (unsigned long *) table->extra2;
>>>
>>> This leads to bogus bounds check for the sysctl value.
>>>
>>> The bug is added in commit:
>>>
>>> commit 9eefe520c814f6f62c5d36a2ddcd3fb99dfdb30e
>>> Author: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
>>> Date: Fri Jul 25 01:48:08 2008 -0700
>>>
>>> Later zero and one were used in a bunch of other ctl_table's.
>>>
>>
>> I think you are blaming wrong commit. This bug was introduced by
>> ed4d4902ebdd7ca8b5a51daaf6bebf4b172895cc ("mm, hugetlb: remove hugetlb_zero and hugetlb_infinity")
>>
>> We have two options to fix this. Reintroduce back hugetlb_zero or make 'zero' unsigned long instead.
>> I would prefer the latter, changing type to 'unsigned long' shouldn't harm any other users of this variable.
>>
>
> ipc/ipc_sysctl.c also contains zero, one and int_max variables that
> are used in a similar way:
>

Yes, but they all look correct to me. Proc handlers in ipc/ipc_sysctl.c
use proc_dointvec_minmax() so they should be fine with 'int zero'.

But hugetlb_sysctl_handler_common() calls proc_doulongvec_minmax(), therefore it needs 'unsigned long'.

> static int zero;
> static int one = 1;
> static int int_max = INT_MAX;
>

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