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linux/kernel/kcmp.c at master · fabgithub/linux · GitHub
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kcmp.c
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#include
<linux/kernel.h>
#include
<linux/syscalls.h>
#include
<linux/fdtable.h>
#include
<linux/string.h>
#include
<linux/random.h>
#include
<linux/module.h>
#include
<linux/ptrace.h>
#include
<linux/init.h>
#include
<linux/errno.h>
#include
<linux/cache.h>
#include
<linux/bug.h>
#include
<linux/err.h>
#include
<linux/kcmp.h>
#include
<asm/unistd.h>
/*
* We don't expose the real in-memory order of objects for security reasons.
* But still the comparison results should be suitable for sorting. So we
* obfuscate kernel pointers values and compare the production instead.
*
* The obfuscation is done in two steps. First we xor the kernel pointer with
* a random value, which puts pointer into a new position in a reordered space.
* Secondly we multiply the xor production with a large odd random number to
* permute its bits even more (the odd multiplier guarantees that the product
* is unique ever after the high bits are truncated, since any odd number is
* relative prime to 2^n).
*
* Note also that the obfuscation itself is invisible to userspace and if needed
* it can be changed to an alternate scheme.
*/
static
unsigned long
cookies
[
KCMP_TYPES
][
2
]
__read_mostly
;
static
long
kptr_obfuscate
(
long
v
,
int
type
)
{
return
(
v
^
cookies
[
type
][
0
])
*
cookies
[
type
][
1
];
}
/*
* 0 - equal, i.e. v1 = v2
* 1 - less than, i.e. v1 < v2
* 2 - greater than, i.e. v1 > v2
* 3 - not equal but ordering unavailable (reserved for future)
*/
static
int
kcmp_ptr
(
void
*
v1
,
void
*
v2
,
enum
kcmp_type
type
)
{
long
ret
;
ret
=
kptr_obfuscate
((
long
)
v1
,
type
)
-
kptr_obfuscate
((
long
)
v2
,
type
);
return
(
ret
<
0
) | ((
ret
>
0
) <<
1
);
}
/* The caller must have pinned the task */
static
struct
file
*
get_file_raw_ptr
(
struct
task_struct
*
task
,
unsigned
int
idx
)
{
struct
file
*
file
=
NULL
;
task_lock
(
task
);
rcu_read_lock
();
if
(
task
->
files
)
file
=
fcheck_files
(
task
->
files
,
idx
);
rcu_read_unlock
();
task_unlock
(
task
);
return
file
;
}
static
void
kcmp_unlock
(
struct
mutex
*
m1
,
struct
mutex
*
m2
)
{
if
(
likely
(
m2
!=
m1
))
mutex_unlock
(
m2
);
mutex_unlock
(
m1
);
}
static
int
kcmp_lock
(
struct
mutex
*
m1
,
struct
mutex
*
m2
)
{
int
err
;
if
(
m2
>
m1
)
swap
(
m1
,
m2
);
err
=
mutex_lock_killable
(
m1
);
if
(!
err
&&
likely
(
m1
!=
m2
)) {
err
=
mutex_lock_killable_nested
(
m2
,
SINGLE_DEPTH_NESTING
);
if
(
err
)
mutex_unlock
(
m1
);
}
return
err
;
}
SYSCALL_DEFINE5
(
kcmp
,
pid_t
,
pid1
,
pid_t
,
pid2
,
int
,
type
,
unsigned
long
,
idx1
,
unsigned
long
,
idx2
)
{
struct
task_struct
*
task1
,
*
task2
;
int
ret
;
rcu_read_lock
();
/*
* Tasks are looked up in caller's PID namespace only.
*/
task1
=
find_task_by_vpid
(
pid1
);
task2
=
find_task_by_vpid
(
pid2
);
if
(!
task1
||
!
task2
)
goto
err_no_task
;
get_task_struct
(
task1
);
get_task_struct
(
task2
);
rcu_read_unlock
();
/*
* One should have enough rights to inspect task details.
*/
ret
=
kcmp_lock
(
&
task1
->
signal
->
cred_guard_mutex
,
&
task2
->
signal
->
cred_guard_mutex
);
if
(
ret
)
goto
err
;
if
(!
ptrace_may_access
(
task1
,
PTRACE_MODE_READ
)
||
!
ptrace_may_access
(
task2
,
PTRACE_MODE_READ
)) {
ret
=
-
EPERM
;
goto
err_unlock
;
}
switch
(
type
) {
case
KCMP_FILE
: {
struct
file
*
filp1
,
*
filp2
;
filp1
=
get_file_raw_ptr
(
task1
,
idx1
);
filp2
=
get_file_raw_ptr
(
task2
,
idx2
);
if
(
filp1
&&
filp2
)
ret
=
kcmp_ptr
(
filp1
,
filp2
,
KCMP_FILE
);
else
ret
=
-
EBADF
;
break
;
}
case
KCMP_VM
:
ret
=
kcmp_ptr
(
task1
->
mm
,
task2
->
mm
,
KCMP_VM
);
break
;
case
KCMP_FILES
:
ret
=
kcmp_ptr
(
task1
->
files
,
task2
->
files
,
KCMP_FILES
);
break
;
case
KCMP_FS
:
ret
=
kcmp_ptr
(
task1
->
fs
,
task2
->
fs
,
KCMP_FS
);
break
;
case
KCMP_SIGHAND
:
ret
=
kcmp_ptr
(
task1
->
sighand
,
task2
->
sighand
,
KCMP_SIGHAND
);
break
;
case
KCMP_IO
:
ret
=
kcmp_ptr
(
task1
->
io_context
,
task2
->
io_context
,
KCMP_IO
);
break
;
case
KCMP_SYSVSEM
:
#ifdef
CONFIG_SYSVIPC
ret
=
kcmp_ptr
(
task1
->
sysvsem
.
undo_list
,
task2
->
sysvsem
.
undo_list
,
KCMP_SYSVSEM
);
#else
ret
=
-
EOPNOTSUPP
;
#endif
break
;
default
:
ret
=
-
EINVAL
;
break
;
}
err_unlock
:
kcmp_unlock
(
&
task1
->
signal
->
cred_guard_mutex
,
&
task2
->
signal
->
cred_guard_mutex
);
err
:
put_task_struct
(
task1
);
put_task_struct
(
task2
);
return
ret
;
err_no_task
:
rcu_read_unlock
();
return
-
ESRCH
;
}
static
__init
int
kcmp_cookies_init
(
void
)
{
int
i
;
get_random_bytes
(
cookies
,
sizeof
(
cookies
));
for
(
i
=
0
;
i
<
KCMP_TYPES
;
i
++
)
cookies
[
i
][
1
] |= (~(~
0UL
>>
1
) |
1
);
return
0
;
}
arch_initcall
(
kcmp_cookies_init
);
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