fs,userns: Change inode_capable to capable_wrt_inode_uidgid

The kernel has no concept of capabilities with respect to inodes; inodes
exist independently of namespaces.  For example, inode_capable(inode,
CAP_LINUX_IMMUTABLE) would be nonsense.

This patch changes inode_capable to check for uid and gid mappings and
renames it to capable_wrt_inode_uidgid, which should make it more
obvious what it does.

Fixes CVE-2014-4014.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 27 insertions, 26 deletions

diff --git a/fs/attr.c b/fs/attr.c
index 5d4e59d56e85..6530ced19697 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -50,14 +50,14 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr)
         if ((ia_valid & ATTR_UID) &&
             (!uid_eq(current_fsuid(), inode->i_uid) ||
              !uid_eq(attr->ia_uid, inode->i_uid)) &&
-            !inode_capable(inode, CAP_CHOWN))
+            !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
                 return -EPERM;
 
         /* Make sure caller can chgrp. */
         if ((ia_valid & ATTR_GID) &&
             (!uid_eq(current_fsuid(), inode->i_uid) ||
             (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
-            !inode_capable(inode, CAP_CHOWN))
+            !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
                 return -EPERM;
 
         /* Make sure a caller can chmod. */
@@ -67,7 +67,7 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr)
                 /* Also check the setgid bit! */
                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
                                 inode->i_gid) &&
-                    !inode_capable(inode, CAP_FSETID))
+                    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
                         attr->ia_mode &= ~S_ISGID;
         }
 
@@ -160,7 +160,7 @@ void setattr_copy(struct inode *inode, const struct iattr *attr)
                 umode_t mode = attr->ia_mode;
 
                 if (!in_group_p(inode->i_gid) &&
-                    !inode_capable(inode, CAP_FSETID))
+                    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
                         mode &= ~S_ISGID;
                 inode->i_mode = mode;
         }
diff --git a/fs/inode.c b/fs/inode.c
index 2feb9b69f1be..6eecb7ff0b9a 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1839,14 +1839,18 @@ EXPORT_SYMBOL(inode_init_owner);
  * inode_owner_or_capable - check current task permissions to inode
  * @inode: inode being checked
  *
- * Return true if current either has CAP_FOWNER to the inode, or
- * owns the file.
+ * Return true if current either has CAP_FOWNER in a namespace with the
+ * inode owner uid mapped, or owns the file.
  */
 bool inode_owner_or_capable(const struct inode *inode)
 {
+        struct user_namespace *ns;
+
         if (uid_eq(current_fsuid(), inode->i_uid))
                 return true;
-        if (inode_capable(inode, CAP_FOWNER))
+
+        ns = current_user_ns();
+        if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
                 return true;
         return false;
 }
diff --git a/fs/namei.c b/fs/namei.c
index 80168273396b..985c6f368485 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -332,10 +332,11 @@ int generic_permission(struct inode *inode, int mask)
 
         if (S_ISDIR(inode->i_mode)) {
                 /* DACs are overridable for directories */
-                if (inode_capable(inode, CAP_DAC_OVERRIDE))
+                if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
                         return 0;
                 if (!(mask & MAY_WRITE))
-                        if (inode_capable(inode, CAP_DAC_READ_SEARCH))
+                        if (capable_wrt_inode_uidgid(inode,
+                                                     CAP_DAC_READ_SEARCH))
                                 return 0;
                 return -EACCES;
         }
@@ -345,7 +346,7 @@ int generic_permission(struct inode *inode, int mask)
          * at least one exec bit set.
          */
         if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
-                if (inode_capable(inode, CAP_DAC_OVERRIDE))
+                if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
                         return 0;
 
         /*
@@ -353,7 +354,7 @@ int generic_permission(struct inode *inode, int mask)
          */
         mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
         if (mask == MAY_READ)
-                if (inode_capable(inode, CAP_DAC_READ_SEARCH))
+                if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH))
                         return 0;
 
         return -EACCES;
@@ -2379,7 +2380,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
                 return 0;
         if (uid_eq(dir->i_uid, fsuid))
                 return 0;
-        return !inode_capable(inode, CAP_FOWNER);
+        return !capable_wrt_inode_uidgid(inode, CAP_FOWNER);
 }
 
 /*
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 0b18776b075e..6152cbe353e8 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1215,7 +1215,7 @@ xfs_ioctl_setattr(
                  * cleared upon successful return from chown()
                  */
                 if ((ip->i_d.di_mode & (S_ISUID|S_ISGID)) &&
-                    !inode_capable(VFS_I(ip), CAP_FSETID))
+                    !capable_wrt_inode_uidgid(VFS_I(ip), CAP_FSETID))
                         ip->i_d.di_mode &= ~(S_ISUID|S_ISGID);
 
                 /*
diff --git a/include/linux/capability.h b/include/linux/capability.h
index a6ee1f9a5018..84b13ad67c1c 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -210,7 +210,7 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
                                       struct user_namespace *ns, int cap);
 extern bool capable(int cap);
 extern bool ns_capable(struct user_namespace *ns, int cap);
-extern bool inode_capable(const struct inode *inode, int cap);
+extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
 extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
 
 /* audit system wants to get cap info from files as well */
diff --git a/kernel/capability.c b/kernel/capability.c
index 84b2bbf443e7..a5cf13c018ce 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -424,23 +424,19 @@ bool capable(int cap)
 EXPORT_SYMBOL(capable);
 
 /**
- * inode_capable - Check superior capability over inode
+ * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
  * @inode: The inode in question
  * @cap: The capability in question
  *
- * Return true if the current task has the given superior capability
- * targeted at it's own user namespace and that the given inode is owned
- * by the current user namespace or a child namespace.
- *
- * Currently we check to see if an inode is owned by the current
- * user namespace by seeing if the inode's owner maps into the
- * current user namespace.
- *
+ * Return true if the current task has the given capability targeted at
+ * its own user namespace and that the given inode's uid and gid are
+ * mapped into the current user namespace.
  */
-bool inode_capable(const struct inode *inode, int cap)
+bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 {
         struct user_namespace *ns = current_user_ns();
 
-        return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid);
+        return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
+                kgid_has_mapping(ns, inode->i_gid);
 }
-EXPORT_SYMBOL(inode_capable);
+EXPORT_SYMBOL(capable_wrt_inode_uidgid);