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CRED: Allow kernel services to override LSM settings for task actions

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Allow kernel services to override LSM settings appropriate to the actions
performed by a task by duplicating a set of credentials, modifying it and then
using task_struct::cred to point to it when performing operations on behalf of
a task.

This is used, for example, by CacheFiles which has to transparently access the
cache on behalf of a process that thinks it is doing, say, NFS accesses with a
potentially inappropriate (with respect to accessing the cache) set of
credentials.

This patch provides two LSM hooks for modifying a task security record:

 (*) security_kernel_act_as() which allows modification of the security datum
     with which a task acts on other objects (most notably files).

 (*) security_kernel_create_files_as() which allows modification of the
     security datum that is used to initialise the security data on a file that
     a task creates.

The patch also provides four new credentials handling functions, which wrap the
LSM functions:

 (1) prepare_kernel_cred()

     Prepare a set of credentials for a kernel service to use, based either on
     a daemon's credentials or on init_cred.  All the keyrings are cleared.

 (2) set_security_override()

     Set the LSM security ID in a set of credentials to a specific security
     context, assuming permission from the LSM policy.

 (3) set_security_override_from_ctx()

     As (2), but takes the security context as a string.

 (4) set_create_files_as()

     Set the file creation LSM security ID in a set of credentials to be the
     same as that on a particular inode.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> [Smack changes]
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
David Howells
2008-11-14 10:39:28 +11:00
committed by James Morris
parent 1bfdc75ae0
commit 3a3b7ce933
7 changed files with 252 additions and 0 deletions
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28
include/linux/security.h
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@ -587,6 +587,19 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
* @new points to the new credentials.
* @old points to the original credentials.
* Install a new set of credentials.
* @kernel_act_as:
* Set the credentials for a kernel service to act as (subjective context).
* @new points to the credentials to be modified.
* @secid specifies the security ID to be set
* The current task must be the one that nominated @secid.
* Return 0 if successful.
* @kernel_create_files_as:
* Set the file creation context in a set of credentials to be the same as
* the objective context of the specified inode.
* @new points to the credentials to be modified.
* @inode points to the inode to use as a reference.
* The current task must be the one that nominated @inode.
* Return 0 if successful.
* @task_setuid:
* Check permission before setting one or more of the user identity
* attributes of the current process. The @flags parameter indicates
@ -1381,6 +1394,8 @@ struct security_operations {
int (*cred_prepare)(struct cred *new, const struct cred *old,
gfp_t gfp);
void (*cred_commit)(struct cred *new, const struct cred *old);
int (*kernel_act_as)(struct cred *new, u32 secid);
int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
int (*task_setuid) (uid_t id0, uid_t id1, uid_t id2, int flags);
int (*task_fix_setuid) (struct cred *new, const struct cred *old,
int flags);
@ -1632,6 +1647,8 @@ int security_task_create(unsigned long clone_flags);
void security_cred_free(struct cred *cred);
int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
void security_commit_creds(struct cred *new, const struct cred *old);
int security_kernel_act_as(struct cred *new, u32 secid);
int security_kernel_create_files_as(struct cred *new, struct inode *inode);
int security_task_setuid(uid_t id0, uid_t id1, uid_t id2, int flags);
int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags);
@ -2151,6 +2168,17 @@ static inline void security_commit_creds(struct cred *new,
{
}
static inline int security_kernel_act_as(struct cred *cred, u32 secid)
{
return 0;
}
static inline int security_kernel_create_files_as(struct cred *cred,
struct inode *inode)
{
return 0;
}
static inline int security_task_setuid(uid_t id0, uid_t id1, uid_t id2,
int flags)
{