[PATCH 06b/26] Security: Make NFSD work with detached security

[David Howells <dhowells@redhat.com>]

Make NFSD work with detached security, using the patches that excise the
security information from task_struct to struct task_security as a base.

Each time NFSD wants a new security descriptor (to do NFS4 recovery or just to
do NFS operations), a task_security record is derived from NFSD's *objective*
security, modified and then applied as the *subjective* security.  This means
(a) the changes are not visible to anyone looking at NFSD through /proc, (b)
there is no leakage between two consecutive ops with different security
configurations.

Consideration should probably be given to caching the task_security record on
the basis that there'll probably be several ops that will want to use any
particular security configuration.

Furthermore, nfs4recover.c perhaps ought to set an appropriate LSM context on
the record pointed to by rec_security so that the disk is accessed
appropriately (see set_security_override[_from_ctx]()).

NOTE!  This patch must be and will be rolled in to patch 06 of 26 to make the
latter compile fully, however it may be useful to the nfsd maintainers to see
it as a separate patch.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/nfsd/auth.c        |   31 +++++++++++++++++-------
 fs/nfsd/nfs4recover.c |   64 +++++++++++++++++++++++++++++++------------------
 include/linux/sched.h |    1 +
 kernel/sys.c          |   27 ++++++++++++++++++---
 4 files changed, 86 insertions(+), 37 deletions(-)


diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
index 2192805..462d989 100644
--- a/fs/nfsd/auth.c
+++ b/fs/nfsd/auth.c
@@ -6,6 +6,7 @@
 
 #include <linux/types.h>
 #include <linux/sched.h>
+#include <linux/cred.h>
 #include <linux/sunrpc/svc.h>
 #include <linux/sunrpc/svcauth.h>
 #include <linux/nfsd/nfsd.h>
@@ -28,11 +29,17 @@ int nfsexp_flags(struct svc_rqst *rqstp, struct svc_export *exp)
 
 int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 {
+	struct task_security *sec, *old;
 	struct svc_cred	cred = rqstp->rq_cred;
 	int i;
 	int flags = nfsexp_flags(rqstp, exp);
 	int ret;
 
+	/* derive the new security record from nfsd's objective security */
+	sec = get_kernel_security(current);
+	if (!sec)
+		return -ENOMEM;
+
 	if (flags & NFSEXP_ALLSQUASH) {
 		cred.cr_uid = exp->ex_anon_uid;
 		cred.cr_gid = exp->ex_anon_gid;
@@ -56,23 +63,29 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
 		get_group_info(cred.cr_group_info);
 
 	if (cred.cr_uid != (uid_t) -1)
-		current->fsuid = cred.cr_uid;
+		sec->fsuid = cred.cr_uid;
 	else
-		current->fsuid = exp->ex_anon_uid;
+		sec->fsuid = exp->ex_anon_uid;
 	if (cred.cr_gid != (gid_t) -1)
-		current->fsgid = cred.cr_gid;
+		sec->fsgid = cred.cr_gid;
 	else
-		current->fsgid = exp->ex_anon_gid;
+		sec->fsgid = exp->ex_anon_gid;
 
-	if (!cred.cr_group_info)
+	if (!cred.cr_group_info) {
+		put_task_security(sec);
 		return -ENOMEM;
-	ret = set_current_groups(cred.cr_group_info);
+	}
+	ret = set_groups(sec, cred.cr_group_info);
 	put_group_info(cred.cr_group_info);
 	if ((cred.cr_uid)) {
-		cap_t(current->cap_effective) &= ~CAP_NFSD_MASK;
+		cap_t(sec->cap_effective) &= ~CAP_NFSD_MASK;
 	} else {
-		cap_t(current->cap_effective) |= (CAP_NFSD_MASK &
-						  current->cap_permitted);
+		cap_t(sec->cap_effective) |= CAP_NFSD_MASK & sec->cap_permitted;
 	}
+
+	/* set the new security as nfsd's subjective security */
+	old = current->act_as;
+	current->act_as = sec;
+	put_task_security(old);
 	return ret;
 }
diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 1602cd0..ae91262 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -46,27 +46,37 @@
 #include <linux/scatterlist.h>
 #include <linux/crypto.h>
 #include <linux/sched.h>
+#include <linux/cred.h>
 
 #define NFSDDBG_FACILITY                NFSDDBG_PROC
 
 /* Globals */
 static struct nameidata rec_dir;
 static int rec_dir_init = 0;
+static struct task_security *rec_security;
 
+/*
+ * switch the special recovery access security in on the current task's
+ * subjective security
+ */
 static void
-nfs4_save_user(uid_t *saveuid, gid_t *savegid)
+nfs4_begin_secure(struct task_security **saved_sec)
 {
-	*saveuid = current->fsuid;
-	*savegid = current->fsgid;
-	current->fsuid = 0;
-	current->fsgid = 0;
+	*saved_sec = current->act_as;
+	current->act_as = get_task_security(rec_security);
 }
 
+/*
+ * return the current task's subjective security to its former glory
+ */
 static void
-nfs4_reset_user(uid_t saveuid, gid_t savegid)
+nfs4_end_secure(struct task_security *saved_sec)
 {
-	current->fsuid = saveuid;
-	current->fsgid = savegid;
+	struct task_security *discard;
+
+	discard = current->act_as;
+	current->act_as = saved_sec;
+	put_task_security(discard);
 }
 
 static void
@@ -128,10 +138,9 @@ nfsd4_sync_rec_dir(void)
 int
 nfsd4_create_clid_dir(struct nfs4_client *clp)
 {
+	struct task_security *saved_sec;
 	char *dname = clp->cl_recdir;
 	struct dentry *dentry;
-	uid_t uid;
-	gid_t gid;
 	int status;
 
 	dprintk("NFSD: nfsd4_create_clid_dir for \"%s\"\n", dname);
@@ -139,7 +148,7 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
 	if (!rec_dir_init || clp->cl_firststate)
 		return 0;
 
-	nfs4_save_user(&uid, &gid);
+	nfs4_begin_secure(&saved_sec);
 
 	/* lock the parent */
 	mutex_lock(&rec_dir.dentry->d_inode->i_mutex);
@@ -163,7 +172,7 @@ out_unlock:
 		clp->cl_firststate = 1;
 		nfsd4_sync_rec_dir();
 	}
-	nfs4_reset_user(uid, gid);
+	nfs4_end_secure(saved_sec);
 	dprintk("NFSD: nfsd4_create_clid_dir returns %d\n", status);
 	return status;
 }
@@ -206,20 +215,19 @@ nfsd4_build_dentrylist(void *arg, const char *name, int namlen,
 static int
 nfsd4_list_rec_dir(struct dentry *dir, recdir_func *f)
 {
+	struct task_security *saved_sec;
 	struct file *filp;
 	struct dentry_list_arg dla = {
 		.parent = dir,
 	};
 	struct list_head *dentries = &dla.dentries;
 	struct dentry_list *child;
-	uid_t uid;
-	gid_t gid;
 	int status;
 
 	if (!rec_dir_init)
 		return 0;
 
-	nfs4_save_user(&uid, &gid);
+	nfs4_begin_secure(&saved_sec);
 
 	filp = dentry_open(dget(dir), mntget(rec_dir.mnt), O_RDONLY);
 	status = PTR_ERR(filp);
@@ -244,7 +252,7 @@ out:
 		dput(child->dentry);
 		kfree(child);
 	}
-	nfs4_reset_user(uid, gid);
+	nfs4_end_secure(saved_sec);
 	return status;
 }
 
@@ -306,17 +314,16 @@ out:
 void
 nfsd4_remove_clid_dir(struct nfs4_client *clp)
 {
-	uid_t uid;
-	gid_t gid;
+	struct task_security *saved_sec;
 	int status;
 
 	if (!rec_dir_init || !clp->cl_firststate)
 		return;
 
 	clp->cl_firststate = 0;
-	nfs4_save_user(&uid, &gid);
+	nfs4_begin_secure(&saved_sec);
 	status = nfsd4_unlink_clid_dir(clp->cl_recdir, HEXDIR_LEN-1);
-	nfs4_reset_user(uid, gid);
+	nfs4_end_secure(saved_sec);
 	if (status == 0)
 		nfsd4_sync_rec_dir();
 	if (status)
@@ -387,8 +394,7 @@ nfsd4_recdir_load(void) {
 void
 nfsd4_init_recdir(char *rec_dirname)
 {
-	uid_t			uid = 0;
-	gid_t			gid = 0;
+	struct task_security	*saved_sec;
 	int 			status;
 
 	printk("NFSD: Using %s as the NFSv4 state recovery directory\n",
@@ -396,7 +402,15 @@ nfsd4_init_recdir(char *rec_dirname)
 
 	BUG_ON(rec_dir_init);
 
-	nfs4_save_user(&uid, &gid);
+	/* derive the security record from this task's objective security */
+	rec_security = get_kernel_security(current);
+	if (!rec_security) {
+		printk("NFSD:"
+		       " unable to allocate recovery directory security\n");
+		return;
+	}
+
+	nfs4_begin_secure(&saved_sec);
 
 	status = path_lookup(rec_dirname, LOOKUP_FOLLOW | LOOKUP_DIRECTORY,
 			&rec_dir);
@@ -406,7 +420,8 @@ nfsd4_init_recdir(char *rec_dirname)
 
 	if (!status)
 		rec_dir_init = 1;
-	nfs4_reset_user(uid, gid);
+
+	nfs4_end_secure(saved_sec);
 }
 
 void
@@ -416,4 +431,5 @@ nfsd4_shutdown_recdir(void)
 		return;
 	rec_dir_init = 0;
 	path_release(&rec_dir);
+	put_task_security(rec_security);
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 697e707..d079b85 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -886,6 +886,7 @@ struct group_info {
 extern struct group_info *groups_alloc(int gidsetsize);
 extern void groups_free(struct group_info *group_info);
 extern int set_current_groups(struct group_info *group_info);
+extern int set_groups(struct task_security *sec, struct group_info *group_info);
 extern int groups_search(struct group_info *group_info, gid_t grp);
 /* access the groups "array" with this macro */
 #define GROUP_AT(gi, i) \
diff --git a/kernel/sys.c b/kernel/sys.c
index e331b6f..790639f 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1245,10 +1245,16 @@ int groups_search(struct group_info *group_info, gid_t grp)
 	return 0;
 }
 
-/* validate and set current->group_info */
-int set_current_groups(struct group_info *group_info)
+/**
+ * set_groups - Change a group subscription in a security record
+ * @sec: The security record to alter
+ * @group_info: The group list to impose
+ *
+ * Validate a group subscription and, if valid, impose it upon a task security
+ * record.
+ */
+int set_groups(struct task_security *sec, struct group_info *group_info)
 {
-	struct task_security *sec = current->sec;
 	int retval;
 	struct group_info *old_info;
 
@@ -1265,10 +1271,23 @@ int set_current_groups(struct group_info *group_info)
 	spin_unlock(&sec->lock);
 
 	put_group_info(old_info);
-
 	return 0;
 }
 
+EXPORT_SYMBOL(set_groups);
+
+/**
+ * set_current_groups - Change current's group subscription
+ * @group_info: The group list to impose
+ *
+ * Validate a group subscription and, if valid, impose it upon current's task
+ * security record.
+ */
+int set_current_groups(struct group_info *group_info)
+{
+	return set_groups(current->sec, group_info);
+}
+
 EXPORT_SYMBOL(set_current_groups);
 
 asmlinkage long sys_getgroups(int gidsetsize, gid_t __user *grouplist)