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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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37
security/smack/smack_lsm.c
View File

@@ -1011,6 +1011,41 @@ static void smack_cred_commit(struct cred *new, const struct cred *old)
{
}
/**
* smack_kernel_act_as - Set the subjective context in a set of credentials
* @new points to the set of credentials to be modified.
* @secid specifies the security ID to be set
*
* Set the security data for a kernel service.
*/
static int smack_kernel_act_as(struct cred *new, u32 secid)
{
char *smack = smack_from_secid(secid);
if (smack == NULL)
return -EINVAL;
new->security = smack;
return 0;
}
/**
* smack_kernel_create_files_as - Set the file creation label in a set of creds
* @new points to the set of credentials to be modified
* @inode points to the inode to use as a reference
*
* Set the file creation context in a set of credentials to the same
* as the objective context of the specified inode
*/
static int smack_kernel_create_files_as(struct cred *new,
struct inode *inode)
{
struct inode_smack *isp = inode->i_security;
new->security = isp->smk_inode;
return 0;
}
/**
* smack_task_setpgid - Smack check on setting pgid
* @p: the task object
@@ -2641,6 +2676,8 @@ struct security_operations smack_ops = {
.cred_free = smack_cred_free,
.cred_prepare = smack_cred_prepare,
.cred_commit = smack_cred_commit,
.kernel_act_as = smack_kernel_act_as,
.kernel_create_files_as = smack_kernel_create_files_as,
.task_fix_setuid = cap_task_fix_setuid,
.task_setpgid = smack_task_setpgid,
.task_getpgid = smack_task_getpgid,