Re: Out-of-bounds access in __do_proc_doulongvec_minmax

[Dmitry Vyukov]

On Wed, Dec 3, 2014 at 4:37 PM, Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> wrote:
> 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'.


Ah, OK, I think you are right. I actually had a bug in the code that
determines exact global involved. So it is very possible that it's
another '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;
>>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/