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

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>

1 files changed, 21 insertions, 8 deletions

diff --git a/include/linux/capability.h b/include/linux/capability.h
index f4ea0dd9a618..fa830f8de032 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -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