selinux: Create a common helper to determine an inode label [ver #3]

Create a common helper function to determine the label for a new inode.
This is then used by:

	- may_create()
	- selinux_dentry_init_security()
	- selinux_inode_init_security()

This will change the behaviour of the functions slightly, bringing them
all into line.

Suggested-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <pmoore@redhat.com>

1 files changed, 41 insertions, 46 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ef310f82717d..f4be0a110788 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1709,6 +1709,32 @@ out:
         return rc;
 }
 
+/*
+ * Determine the label for an inode that might be unioned.
+ */
+static int selinux_determine_inode_label(const struct inode *dir,
+                                         const struct qstr *name,
+                                         u16 tclass,
+                                         u32 *_new_isid)
+{
+        const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
+        const struct inode_security_struct *dsec = dir->i_security;
+        const struct task_security_struct *tsec = current_security();
+
+        if ((sbsec->flags & SE_SBINITIALIZED) &&
+            (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) {
+                *_new_isid = sbsec->mntpoint_sid;
+        } else if ((sbsec->flags & SBLABEL_MNT) &&
+                   tsec->create_sid) {
+                *_new_isid = tsec->create_sid;
+        } else {
+                return security_transition_sid(tsec->sid, dsec->sid, tclass,
+                                               name, _new_isid);
+        }
+
+        return 0;
+}
+
 /* Check whether a task can create a file. */
 static int may_create(struct inode *dir,
                       struct dentry *dentry,
@@ -1725,7 +1751,6 @@ static int may_create(struct inode *dir,
         sbsec = dir->i_sb->s_security;
 
         sid = tsec->sid;
-        newsid = tsec->create_sid;
 
         ad.type = LSM_AUDIT_DATA_DENTRY;
         ad.u.dentry = dentry;
@@ -1736,12 +1761,10 @@ static int may_create(struct inode *dir,
         if (rc)
                 return rc;
 
-        if (!newsid || !(sbsec->flags & SBLABEL_MNT)) {
-                rc = security_transition_sid(sid, dsec->sid, tclass,
-                                             &dentry->d_name, &newsid);
-                if (rc)
-                        return rc;
-        }
+        rc = selinux_determine_inode_label(dir, &dentry->d_name, tclass,
+                                           &newsid);
+        if (rc)
+                return rc;
 
         rc = avc_has_perm(sid, newsid, tclass, FILE__CREATE, &ad);
         if (rc)
@@ -2715,32 +2738,14 @@ static int selinux_dentry_init_security(struct dentry *dentry, int mode,
                                         struct qstr *name, void **ctx,
                                         u32 *ctxlen)
 {
-        const struct cred *cred = current_cred();
-        struct task_security_struct *tsec;
-        struct inode_security_struct *dsec;
-        struct superblock_security_struct *sbsec;
-        struct inode *dir = d_backing_inode(dentry->d_parent);
         u32 newsid;
         int rc;
 
-        tsec = cred->security;
-        dsec = dir->i_security;
-        sbsec = dir->i_sb->s_security;
-
-        if (tsec->create_sid && sbsec->behavior != SECURITY_FS_USE_MNTPOINT) {
-                newsid = tsec->create_sid;
-        } else {
-                rc = security_transition_sid(tsec->sid, dsec->sid,
-                                             inode_mode_to_security_class(mode),
-                                             name,
-                                             &newsid);
-                if (rc) {
-                        printk(KERN_WARNING
-                                "%s: security_transition_sid failed, rc=%d\n",
-                               __func__, -rc);
-                        return rc;
-                }
-        }
+        rc = selinux_determine_inode_label(d_inode(dentry->d_parent), name,
+                                           inode_mode_to_security_class(mode),
+                                           &newsid);
+        if (rc)
+                return rc;
 
         return security_sid_to_context(newsid, (char **)ctx, ctxlen);
 }
@@ -2763,22 +2768,12 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
         sid = tsec->sid;
         newsid = tsec->create_sid;
 
-        if ((sbsec->flags & SE_SBINITIALIZED) &&
-            (sbsec->behavior == SECURITY_FS_USE_MNTPOINT))
-                newsid = sbsec->mntpoint_sid;
-        else if (!newsid || !(sbsec->flags & SBLABEL_MNT)) {
-                rc = security_transition_sid(sid, dsec->sid,
-                                             inode_mode_to_security_class(inode->i_mode),
-                                             qstr, &newsid);
-                if (rc) {
-                        printk(KERN_WARNING "%s:  "
-                               "security_transition_sid failed, rc=%d (dev=%s "
-                               "ino=%ld)\n",
-                               __func__,
-                               -rc, inode->i_sb->s_id, inode->i_ino);
-                        return rc;
-                }
-        }
+        rc = selinux_determine_inode_label(
+                dir, qstr,
+                inode_mode_to_security_class(inode->i_mode),
+                &newsid);
+        if (rc)
+                return rc;
 
         /* Possibly defer initialization to selinux_complete_init. */
         if (sbsec->flags & SE_SBINITIALIZED) {