Smack: Transmute labels on specified directories

In a situation where Smack access rules allow processes
with multiple labels to write to a directory it is easy
to get into a situation where the directory gets cluttered
with files that the owner can't deal with because while
they could be written to the directory a process at the
label of the directory can't write them. This is generally
the desired behavior, but when it isn't it is a real
issue.

This patch introduces a new attribute SMACK64TRANSMUTE that
instructs Smack to create the file with the label of the directory
under certain circumstances.

A new access mode, "t" for transmute, is made available to
Smack access rules, which are expanded from "rwxa" to "rwxat".
If a file is created in a directory marked as transmutable
and if access was granted to perform the operation by a rule
that included the transmute mode, then the file gets the
Smack label of the directory instead of the Smack label of the
creating process.

Note that this is equivalent to creating an empty file at the
label of the directory and then having the other process write
to it. The transmute scheme requires that both the access rule
allows transmutation and that the directory be explicitly marked.

Signed-off-by: Jarkko Sakkinen <ext-jarkko.2.sakkinen@nokia.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

1 files changed, 50 insertions, 24 deletions

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 7e19afe0e738..05dc4da2e25f 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3,12 +3,14 @@
  *
  *  This file contains the smack hook function implementations.
  *
- *  Author:
+ *  Authors:
  *      Casey Schaufler <casey@schaufler-ca.com>
+ *      Jarkko Sakkinen <ext-jarkko.2.sakkinen@nokia.com>
  *
  *  Copyright (C) 2007 Casey Schaufler <casey@schaufler-ca.com>
  *  Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
  *                Paul Moore <paul.moore@hp.com>
+ *  Copyright (C) 2010 Nokia Corporation
  *
  *      This program is free software; you can redistribute it and/or modify
  *      it under the terms of the GNU General Public License version 2,
@@ -35,6 +37,9 @@
 
 #define task_security(task)     (task_cred_xxx((task), security))
 
+#define TRANS_TRUE      "TRUE"
+#define TRANS_TRUE_SIZE 4
+
 /**
  * smk_fetch - Fetch the smack label from a file.
  * @ip: a pointer to the inode
@@ -468,6 +473,8 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
                                      char **name, void **value, size_t *len)
 {
         char *isp = smk_of_inode(inode);
+        char *dsp = smk_of_inode(dir);
+        u32 may;
 
         if (name) {
                 *name = kstrdup(XATTR_SMACK_SUFFIX, GFP_KERNEL);
@@ -476,6 +483,16 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
         }
 
         if (value) {
+                may = smk_access_entry(smk_of_current(), dsp);
+
+                /*
+                 * If the access rule allows transmutation and
+                 * the directory requests transmutation then
+                 * by all means transmute.
+                 */
+                if (((may & MAY_TRANSMUTE) != 0) && smk_inode_transmutable(dir))
+                        isp = dsp;
+
                 *value = kstrdup(isp, GFP_KERNEL);
                 if (*value == NULL)
                         return -ENOMEM;
@@ -709,6 +726,12 @@ static int smack_inode_setxattr(struct dentry *dentry, const char *name,
                 if (size == 0 || size >= SMK_LABELLEN ||
                     smk_import(value, size) == NULL)
                         rc = -EINVAL;
+        } else if (strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0) {
+                if (!capable(CAP_MAC_ADMIN))
+                        rc = -EPERM;
+                if (size != TRANS_TRUE_SIZE ||
+                    strncmp(value, TRANS_TRUE, TRANS_TRUE_SIZE) != 0)
+                        rc = -EINVAL;
         } else
                 rc = cap_inode_setxattr(dentry, name, value, size, flags);
 
@@ -735,35 +758,23 @@ static int smack_inode_setxattr(struct dentry *dentry, const char *name,
 static void smack_inode_post_setxattr(struct dentry *dentry, const char *name,
                                       const void *value, size_t size, int flags)
 {
-        struct inode_smack *isp;
         char *nsp;
-
-        /*
-         * Not SMACK or SMACKEXEC
-         */
-        if (strcmp(name, XATTR_NAME_SMACK) &&
-            strcmp(name, XATTR_NAME_SMACKEXEC))
-                return;
-
-        isp = dentry->d_inode->i_security;
-
-        /*
-         * No locking is done here. This is a pointer
-         * assignment.
-         */
-        nsp = smk_import(value, size);
+        struct inode_smack *isp = dentry->d_inode->i_security;
 
         if (strcmp(name, XATTR_NAME_SMACK) == 0) {
+                nsp = smk_import(value, size);
                 if (nsp != NULL)
                         isp->smk_inode = nsp;
                 else
                         isp->smk_inode = smack_known_invalid.smk_known;
-        } else {
+        } else if (strcmp(name, XATTR_NAME_SMACKEXEC) == 0) {
+                nsp = smk_import(value, size);
                 if (nsp != NULL)
                         isp->smk_task = nsp;
                 else
                         isp->smk_task = smack_known_invalid.smk_known;
-        }
+        } else if (strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0)
+                isp->smk_flags |= SMK_INODE_TRANSMUTE;
 
         return;
 }
@@ -803,7 +814,8 @@ static int smack_inode_removexattr(struct dentry *dentry, const char *name)
         if (strcmp(name, XATTR_NAME_SMACK) == 0 ||
             strcmp(name, XATTR_NAME_SMACKIPIN) == 0 ||
             strcmp(name, XATTR_NAME_SMACKIPOUT) == 0 ||
-            strcmp(name, XATTR_NAME_SMACKEXEC) == 0) {
+            strcmp(name, XATTR_NAME_SMACKEXEC) == 0 ||
+            strcmp(name, XATTR_NAME_SMACKTRANSMUTE) == 0) {
                 if (!capable(CAP_MAC_ADMIN))
                         rc = -EPERM;
         } else
@@ -2274,6 +2286,8 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
         char *csp = smk_of_current();
         char *fetched;
         char *final;
+        char trattr[TRANS_TRUE_SIZE];
+        int transflag = 0;
         struct dentry *dp;
 
         if (inode == NULL)
@@ -2392,10 +2406,19 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
                  */
                 dp = dget(opt_dentry);
                 fetched = smk_fetch(XATTR_NAME_SMACK, inode, dp);
-                if (fetched != NULL)
+                if (fetched != NULL) {
                         final = fetched;
-                isp->smk_task = smk_fetch(XATTR_NAME_SMACKEXEC, inode,
-                                          dp);
+                        if (S_ISDIR(inode->i_mode)) {
+                                trattr[0] = '\0';
+                                inode->i_op->getxattr(dp,
+                                        XATTR_NAME_SMACKTRANSMUTE,
+                                        trattr, TRANS_TRUE_SIZE);
+                                if (strncmp(trattr, TRANS_TRUE,
+                                            TRANS_TRUE_SIZE) == 0)
+                                        transflag = SMK_INODE_TRANSMUTE;
+                        }
+                }
+                isp->smk_task = smk_fetch(XATTR_NAME_SMACKEXEC, inode, dp);
 
                 dput(dp);
                 break;
@@ -2406,7 +2429,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
         else
                 isp->smk_inode = final;
 
-        isp->smk_flags |= SMK_INODE_INSTANT;
+        isp->smk_flags |= (SMK_INODE_INSTANT | transflag);
 
 unlockandout:
         mutex_unlock(&isp->smk_lock);
@@ -2456,6 +2479,7 @@ static int smack_setprocattr(struct task_struct *p, char *name,
                              void *value, size_t size)
 {
         struct task_smack *tsp;
+        struct task_smack *oldtsp;
         struct cred *new;
         char *newsmack;
 
@@ -2485,6 +2509,7 @@ static int smack_setprocattr(struct task_struct *p, char *name,
         if (newsmack == smack_known_web.smk_known)
                 return -EPERM;
 
+        oldtsp = p->cred->security;
         new = prepare_creds();
         if (new == NULL)
                 return -ENOMEM;
@@ -2494,6 +2519,7 @@ static int smack_setprocattr(struct task_struct *p, char *name,
                 return -ENOMEM;
         }
         tsp->smk_task = newsmack;
+        tsp->smk_forked = oldtsp->smk_forked;
         new->security = tsp;
         commit_creds(new);
         return size;