2007-06-27 17:15:27

by Serge E. Hallyn

Subject: [PATCH 1/1] file capabilities: introduce cap_setfcap

Here's the first patch (of several or many to come) to address some of
Andrew's comments.

Kaigai, IIUC cap_names.h will eventually be automatically updated? (I
had to manually tweak it for testing as the new kernel sources were not
located on the test system)

thanks,
-serge

>From fefcd341e478bd9e490d34abe9efd3c3c4f0b8a0 Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <[email protected]>
Date: Wed, 27 Jun 2007 13:09:20 -0400
Subject: [PATCH 1/1] file capabilities: introduce cap_setfcap

Setting file capabilities previously required the
cap_sys_admin capability, since they are stored as
extended attributes in the security.* namespace.

Introduce CAP_SETFCAP (to mirror CAP_SETPCAP), and
require it for setting file capabilities instead of
CAP_SYS_ADMIN.

Quoting Andrew Morgan,

"CAP_SYS_ADMIN is way too overloaded and this
functionality is special."

Signed-off-by: Serge E. Hallyn <[email protected]>
---
include/linux/capability.h | 4 +++-
security/commoncap.c | 12 ++++++++++--
2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 89125df..cdfaa10 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -324,7 +324,9 @@ typedef __u32 kernel_cap_t;

#define CAP_AUDIT_CONTROL 30

-#define CAP_NUMCAPS 31
+#define CAP_SETFCAP 31
+
+#define CAP_NUMCAPS 32

#ifdef __KERNEL__
/*
diff --git a/security/commoncap.c b/security/commoncap.c
index 4e9ff02..24de4fa 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -290,7 +290,11 @@ int cap_bprm_secureexec (struct linux_binprm *bprm)
int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
size_t size, int flags)
{
- if (!strncmp(name, XATTR_SECURITY_PREFIX,
+ if (!strcmp(name, XATTR_NAME_CAPS)) {
+ if (!capable(CAP_SETFCAP))
+ return -EPERM;
+ return 0;
+ } else if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) &&
!capable(CAP_SYS_ADMIN))
return -EPERM;
@@ -299,7 +303,11 @@ int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,

int cap_inode_removexattr(struct dentry *dentry, char *name)
{
- if (!strncmp(name, XATTR_SECURITY_PREFIX,
+ if (!strcmp(name, XATTR_NAME_CAPS)) {
+ if (!capable(CAP_SETFCAP))
+ return -EPERM;
+ return 0;
+ } else if (!strncmp(name, XATTR_SECURITY_PREFIX,
sizeof(XATTR_SECURITY_PREFIX) - 1) &&
!capable(CAP_SYS_ADMIN))
return -EPERM;
--
1.5.1.1.GIT

2007-06-28 01:34:20

by Kohei KaiGai

Subject: Re: [PATCH 1/1] file capabilities: introduce cap_setfcap

Serge E. Hallyn wrote:
> Here's the first patch (of several or many to come) to address some of
> Andrew's comments.
>
> Kaigai, IIUC cap_names.h will eventually be automatically updated? (I
> had to manually tweak it for testing as the new kernel sources were not
> located on the test system)

The origin of cap_names.h is "/usr/include/linux/capability.h".
Some scripts kicked by Makefile convert it, then cap_names.h will
be generated.

I don't know whether we can expect the kernel headers are always
deployed under "/usr/include/linux", or not.
In Fedora system, the kernel-headers package deploys all headers
there, so cap_names.h will eventually be automatically updated.

Thanks,

> thanks,
> -serge
>
>>From fefcd341e478bd9e490d34abe9efd3c3c4f0b8a0 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <[email protected]>
> Date: Wed, 27 Jun 2007 13:09:20 -0400
> Subject: [PATCH 1/1] file capabilities: introduce cap_setfcap
>
> Setting file capabilities previously required the
> cap_sys_admin capability, since they are stored as
> extended attributes in the security.* namespace.
>
> Introduce CAP_SETFCAP (to mirror CAP_SETPCAP), and
> require it for setting file capabilities instead of
> CAP_SYS_ADMIN.
>
> Quoting Andrew Morgan,
>
> "CAP_SYS_ADMIN is way too overloaded and this
> functionality is special."
>
> Signed-off-by: Serge E. Hallyn <[email protected]>
> ---
> include/linux/capability.h | 4 +++-
> security/commoncap.c | 12 ++++++++++--
> 2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 89125df..cdfaa10 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -324,7 +324,9 @@ typedef __u32 kernel_cap_t;
>
> #define CAP_AUDIT_CONTROL 30
>
> -#define CAP_NUMCAPS 31
> +#define CAP_SETFCAP 31
> +
> +#define CAP_NUMCAPS 32
>
> #ifdef __KERNEL__
> /*
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 4e9ff02..24de4fa 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -290,7 +290,11 @@ int cap_bprm_secureexec (struct linux_binprm *bprm)
> int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
> size_t size, int flags)
> {
> - if (!strncmp(name, XATTR_SECURITY_PREFIX,
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> + if (!capable(CAP_SETFCAP))
> + return -EPERM;
> + return 0;
> + } else if (!strncmp(name, XATTR_SECURITY_PREFIX,
> sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> !capable(CAP_SYS_ADMIN))
> return -EPERM;
> @@ -299,7 +303,11 @@ int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
>
> int cap_inode_removexattr(struct dentry *dentry, char *name)
> {
> - if (!strncmp(name, XATTR_SECURITY_PREFIX,
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> + if (!capable(CAP_SETFCAP))
> + return -EPERM;
> + return 0;
> + } else if (!strncmp(name, XATTR_SECURITY_PREFIX,
> sizeof(XATTR_SECURITY_PREFIX) - 1) &&
> !capable(CAP_SYS_ADMIN))
> return -EPERM;


--
Open Source Software Promotion Center, NEC
KaiGai Kohei <[email protected]>