Out-of-bounds access in __do_proc_doulongvec_minmax

[Dmitry Vyukov]

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

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.
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