From 3a3b7ce9336952ea7b9564d976d068a238976c9d Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 14 Nov 2008 10:39:28 +1100 Subject: CRED: Allow kernel services to override LSM settings for task actions 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 [Smack changes] Signed-off-by: David Howells Signed-off-by: James Morris --- security/smack/smack_lsm.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) (limited to 'security/smack') diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index de396742abf4..8ad48161cef5 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -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, -- cgit v1.2.3