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capabilities: remain source compatible with 32-bit raw legacy capability support.

Browse source 
Source code out there hard-codes a notion of what the
_LINUX_CAPABILITY_VERSION #define means in terms of the semantics of the
raw capability system calls capget() and capset().  Its unfortunate, but
true.

Since the confusing header file has been in a released kernel, there is
software that is erroneously using 64-bit capabilities with the semantics
of 32-bit compatibilities.  These recently compiled programs may suffer
corruption of their memory when sys_getcap() overwrites more memory than
they are coded to expect, and the raising of added capabilities when using
sys_capset().

As such, this patch does a number of things to clean up the situation
for all. It

  1. forces the _LINUX_CAPABILITY_VERSION define to always retain its
     legacy value.

  2. adopts a new #define strategy for the kernel's internal
     implementation of the preferred magic.

  3. deprecates v2 capability magic in favor of a new (v3) magic
     number. The functionality of v3 is entirely equivalent to v2,
     the only difference being that the v2 magic causes the kernel
     to log a "deprecated" warning so the admin can find applications
     that may be using v2 inappropriately.

[User space code continues to be encouraged to use the libcap API which
protects the application from details like this.  libcap-2.10 is the first
to support v3 capabilities.]

Fixes issue reported in https://bugzilla.redhat.com/show_bug.cgi?id=447518.
Thanks to Bojan Smojver for the report.

[akpm@linux-foundation.org: s/depreciate/deprecate/g]
[akpm@linux-foundation.org: be robust about put_user size]
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: Bojan Smojver <bojan@rexursive.com>
Cc: stable@kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
This commit is contained in:
Andrew G. Morgan 2008-05-27 22:05:17 -07:00 committed by Chris Wright
parent cc94bc37d5
commit ca05a99a54
3 changed files with 95 additions and 47 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
fs/proc/array.c
View file

@ -288,7 +288,7 @@ static void render_cap_t(struct seq_file *m, const char *header,
seq_printf(m, "%s", header);
CAP_FOR_EACH_U32(__capi) {
seq_printf(m, "%08x",
a->cap[(_LINUX_CAPABILITY_U32S-1) - __capi]);
a->cap[(_KERNEL_CAPABILITY_U32S-1) - __capi]);
}
seq_printf(m, "\n");
}

29
include/linux/capability.h
View file

@ -31,11 +31,11 @@ struct task_struct;
#define _LINUX_CAPABILITY_VERSION_1 0x19980330
#define _LINUX_CAPABILITY_U32S_1 1
#define _LINUX_CAPABILITY_VERSION_2 0x20071026
#define _LINUX_CAPABILITY_VERSION_2 0x20071026 /* deprecated - use v3 */
#define _LINUX_CAPABILITY_U32S_2 2
#define _LINUX_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_2
#define _LINUX_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_2
#define _LINUX_CAPABILITY_VERSION_3 0x20080522
#define _LINUX_CAPABILITY_U32S_3 2
typedef struct __user_cap_header_struct {
__u32 version;
@ -77,10 +77,23 @@ struct vfs_cap_data {
} data[VFS_CAP_U32];
};
#ifdef __KERNEL__
#ifndef __KERNEL__
/*
* Backwardly compatible definition for source code - trapped in a
* 32-bit world. If you find you need this, please consider using
* libcap to untrap yourself...
*/
#define _LINUX_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_1
#define _LINUX_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_1
#else
#define _KERNEL_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_3
#define _KERNEL_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_3
typedef struct kernel_cap_struct {
__u32 cap[_LINUX_CAPABILITY_U32S];
__u32 cap[_KERNEL_CAPABILITY_U32S];
} kernel_cap_t;
#define _USER_CAP_HEADER_SIZE (sizeof(struct __user_cap_header_struct))
@ -351,7 +364,7 @@ typedef struct kernel_cap_struct {
*/
#define CAP_FOR_EACH_U32(__capi) \
for (__capi = 0; __capi < _LINUX_CAPABILITY_U32S; ++__capi)
for (__capi = 0; __capi < _KERNEL_CAPABILITY_U32S; ++__capi)
# define CAP_FS_MASK_B0 (CAP_TO_MASK(CAP_CHOWN) \
| CAP_TO_MASK(CAP_DAC_OVERRIDE) \
@ -361,7 +374,7 @@ typedef struct kernel_cap_struct {
# define CAP_FS_MASK_B1 (CAP_TO_MASK(CAP_MAC_OVERRIDE))
#if _LINUX_CAPABILITY_U32S != 2
#if _KERNEL_CAPABILITY_U32S != 2
# error Fix up hand-coded capability macro initializers
#else /* HAND-CODED capability initializers */
@ -372,7 +385,7 @@ typedef struct kernel_cap_struct {
# define CAP_NFSD_SET ((kernel_cap_t){{ CAP_FS_MASK_B0|CAP_TO_MASK(CAP_SYS_RESOURCE), \
CAP_FS_MASK_B1 } })
#endif /* _LINUX_CAPABILITY_U32S != 2 */
#endif /* _KERNEL_CAPABILITY_U32S != 2 */
#define CAP_INIT_INH_SET CAP_EMPTY_SET

111
kernel/capability.c
View file

@ -52,6 +52,69 @@ static void warn_legacy_capability_use(void)
}
}
/*
* Version 2 capabilities worked fine, but the linux/capability.h file
* that accompanied their introduction encouraged their use without
* the necessary user-space source code changes. As such, we have
* created a version 3 with equivalent functionality to version 2, but
* with a header change to protect legacy source code from using
* version 2 when it wanted to use version 1. If your system has code
* that trips the following warning, it is using version 2 specific
* capabilities and may be doing so insecurely.
*
* The remedy is to either upgrade your version of libcap (to 2.10+,
* if the application is linked against it), or recompile your
* application with modern kernel headers and this warning will go
* away.
*/
static void warn_deprecated_v2(void)
{
static int warned;
if (!warned) {
char name[sizeof(current->comm)];
printk(KERN_INFO "warning: `%s' uses deprecated v2"
" capabilities in a way that may be insecure.\n",
get_task_comm(name, current));
warned = 1;
}
}
/*
* Version check. Return the number of u32s in each capability flag
* array, or a negative value on error.
*/
static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
{
__u32 version;
if (get_user(version, &header->version))
return -EFAULT;
switch (version) {
case _LINUX_CAPABILITY_VERSION_1:
warn_legacy_capability_use();
*tocopy = _LINUX_CAPABILITY_U32S_1;
break;
case _LINUX_CAPABILITY_VERSION_2:
warn_deprecated_v2();
/*
* fall through - v3 is otherwise equivalent to v2.
*/
case _LINUX_CAPABILITY_VERSION_3:
*tocopy = _LINUX_CAPABILITY_U32S_3;
break;
default:
if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
return -EFAULT;
return -EINVAL;
}
return 0;
}
/*
* For sys_getproccap() and sys_setproccap(), any of the three
* capability set pointers may be NULL -- indicating that that set is
@ -71,27 +134,13 @@ asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr)
{
int ret = 0;
pid_t pid;
__u32 version;
struct task_struct *target;
unsigned tocopy;
kernel_cap_t pE, pI, pP;
if (get_user(version, &header->version))
return -EFAULT;
switch (version) {
case _LINUX_CAPABILITY_VERSION_1:
warn_legacy_capability_use();
tocopy = _LINUX_CAPABILITY_U32S_1;
break;
case _LINUX_CAPABILITY_VERSION_2:
tocopy = _LINUX_CAPABILITY_U32S_2;
break;
default:
if (put_user(_LINUX_CAPABILITY_VERSION, &header->version))
return -EFAULT;
return -EINVAL;
}
ret = cap_validate_magic(header, &tocopy);
if (ret != 0)
return ret;
if (get_user(pid, &header->pid))
return -EFAULT;
@ -118,7 +167,7 @@ out:
spin_unlock(&task_capability_lock);
if (!ret) {
struct __user_cap_data_struct kdata[_LINUX_CAPABILITY_U32S];
struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
unsigned i;
for (i = 0; i < tocopy; i++) {
@ -128,7 +177,7 @@ out:
}
/*
* Note, in the case, tocopy < _LINUX_CAPABILITY_U32S,
* Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
* we silently drop the upper capabilities here. This
* has the effect of making older libcap
* implementations implicitly drop upper capability
@ -240,30 +289,16 @@ static inline int cap_set_all(kernel_cap_t *effective,
*/
asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
{
struct __user_cap_data_struct kdata[_LINUX_CAPABILITY_U32S];
struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
unsigned i, tocopy;
kernel_cap_t inheritable, permitted, effective;
__u32 version;
struct task_struct *target;
int ret;
pid_t pid;
if (get_user(version, &header->version))
return -EFAULT;
switch (version) {
case _LINUX_CAPABILITY_VERSION_1:
warn_legacy_capability_use();
tocopy = _LINUX_CAPABILITY_U32S_1;
break;
case _LINUX_CAPABILITY_VERSION_2:
tocopy = _LINUX_CAPABILITY_U32S_2;
break;
default:
if (put_user(_LINUX_CAPABILITY_VERSION, &header->version))
return -EFAULT;
return -EINVAL;
}
ret = cap_validate_magic(header, &tocopy);
if (ret != 0)
return ret;
if (get_user(pid, &header->pid))
return -EFAULT;
@ -281,7 +316,7 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
permitted.cap[i] = kdata[i].permitted;
inheritable.cap[i] = kdata[i].inheritable;
}
while (i < _LINUX_CAPABILITY_U32S) {
while (i < _KERNEL_CAPABILITY_U32S) {
effective.cap[i] = 0;
permitted.cap[i] = 0;
inheritable.cap[i] = 0;