[PATCH] add a vfs_permission helper

Most permission() calls have a struct nameidata * available.  This helper
takes that as an argument and thus makes sure we pass it down for lookup
intents and prepares for per-mount read-only support where we need a struct
vfsmount for checking whether a file is writeable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

7 files changed, 31 insertions, 15 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 5a4e3acc2e9f..7bbb781b9ac6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -135,7 +135,7 @@ asmlinkage long sys_uselib(const char __user * library)
         if (!S_ISREG(nd.dentry->d_inode->i_mode))
                 goto exit;
 
-        error = permission(nd.dentry->d_inode, MAY_READ | MAY_EXEC, &nd);
+        error = vfs_permission(&nd, MAY_READ | MAY_EXEC);
         if (error)
                 goto exit;
 
@@ -495,7 +495,7 @@ struct file *open_exec(const char *name)
                 file = ERR_PTR(-EACCES);
                 if (!(nd.mnt->mnt_flags & MNT_NOEXEC) &&
                     S_ISREG(inode->i_mode)) {
-                        int err = permission(inode, MAY_EXEC, &nd);
+                        int err = vfs_permission(&nd, MAY_EXEC);
                         if (!err && !(inode->i_mode & 0111))
                                 err = -EACCES;
                         file = ERR_PTR(err);
diff --git a/fs/inotify.c b/fs/inotify.c
index 9fbaebfdf40b..bf7ce1d2412b 100644
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -372,7 +372,7 @@ static int find_inode(const char __user *dirname, struct nameidata *nd)
         if (error)
                 return error;
         /* you can only watch an inode if you have read permissions on it */
-        error = permission(nd->dentry->d_inode, MAY_READ, NULL);
+        error = vfs_permission(nd, MAY_READ);
         if (error) 
                 path_release(nd);
         return error;
diff --git a/fs/namei.c b/fs/namei.c
index b3f8a1966c9c..25e4ab4ce8b7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -256,6 +256,21 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
         return security_inode_permission(inode, mask, nd);
 }
 
+/**
+ * vfs_permission  -  check for access rights to a given path
+ * @nd:         lookup result that describes the path
+ * @mask:       right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
+ *
+ * Used to check for read/write/execute permissions on a path.
+ * We use "fsuid" for this, letting us set arbitrary permissions
+ * for filesystem access without changing the "normal" uids which
+ * are used for other things.
+ */
+int vfs_permission(struct nameidata *nd, int mask)
+{
+        return permission(nd->dentry->d_inode, mask, nd);
+}
+
 /*
  * get_write_access() gets write permission for a file.
  * put_write_access() releases this write permission.
@@ -765,9 +780,8 @@ static fastcall int __link_path_walk(const char * name, struct nameidata *nd)
 
                 nd->flags |= LOOKUP_CONTINUE;
                 err = exec_permission_lite(inode, nd);
-                if (err == -EAGAIN) { 
-                        err = permission(inode, MAY_EXEC, nd);
-                }
+                if (err == -EAGAIN)
+                        err = vfs_permission(nd, MAY_EXEC);
                 if (err)
                         break;
 
@@ -1407,7 +1421,7 @@ int may_open(struct nameidata *nd, int acc_mode, int flag)
         if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE))
                 return -EISDIR;
 
-        error = permission(inode, acc_mode, nd);
+        error = vfs_permission(nd, acc_mode);
         if (error)
                 return error;
 
@@ -2536,6 +2550,7 @@ EXPORT_SYMBOL(path_lookup);
 EXPORT_SYMBOL(path_release);
 EXPORT_SYMBOL(path_walk);
 EXPORT_SYMBOL(permission);
+EXPORT_SYMBOL(vfs_permission);
 EXPORT_SYMBOL(unlock_rename);
 EXPORT_SYMBOL(vfs_create);
 EXPORT_SYMBOL(vfs_follow_link);
diff --git a/fs/namespace.c b/fs/namespace.c
index caa9187f67e5..2019899f2ab8 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -637,7 +637,7 @@ static int mount_is_safe(struct nameidata *nd)
                 if (current->uid != nd->dentry->d_inode->i_uid)
                         return -EPERM;
         }
-        if (permission(nd->dentry->d_inode, MAY_WRITE, nd))
+        if (vfs_permission(nd, MAY_WRITE))
                 return -EPERM;
         return 0;
 #endif
diff --git a/fs/open.c b/fs/open.c
index 6e8136751e9a..baffc084580d 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -240,7 +240,7 @@ static inline long do_sys_truncate(const char __user * path, loff_t length)
         if (!S_ISREG(inode->i_mode))
                 goto dput_and_out;
 
-        error = permission(inode,MAY_WRITE,&nd);
+        error = vfs_permission(&nd, MAY_WRITE);
         if (error)
                 goto dput_and_out;
 
@@ -394,7 +394,7 @@ asmlinkage long sys_utime(char __user * filename, struct utimbuf __user * times)
                         goto dput_and_out;
 
                 if (current->fsuid != inode->i_uid &&
-                    (error = permission(inode,MAY_WRITE,&nd)) != 0)
+                    (error = vfs_permission(&nd, MAY_WRITE)) != 0)
                         goto dput_and_out;
         }
         down(&inode->i_sem);
@@ -447,7 +447,7 @@ long do_utimes(char __user * filename, struct timeval * times)
                         goto dput_and_out;
 
                 if (current->fsuid != inode->i_uid &&
-                    (error = permission(inode,MAY_WRITE,&nd)) != 0)
+                    (error = vfs_permission(&nd, MAY_WRITE)) != 0)
                         goto dput_and_out;
         }
         down(&inode->i_sem);
@@ -506,7 +506,7 @@ asmlinkage long sys_access(const char __user * filename, int mode)
 
         res = __user_walk(filename, LOOKUP_FOLLOW|LOOKUP_ACCESS, &nd);
         if (!res) {
-                res = permission(nd.dentry->d_inode, mode, &nd);
+                res = vfs_permission(&nd, mode);
                 /* SuS v2 requires we report a read only fs too */
                 if(!res && (mode & S_IWOTH) && IS_RDONLY(nd.dentry->d_inode)
                    && !special_file(nd.dentry->d_inode->i_mode))
@@ -530,7 +530,7 @@ asmlinkage long sys_chdir(const char __user * filename)
         if (error)
                 goto out;
 
-        error = permission(nd.dentry->d_inode,MAY_EXEC,&nd);
+        error = vfs_permission(&nd, MAY_EXEC);
         if (error)
                 goto dput_and_out;
 
@@ -581,7 +581,7 @@ asmlinkage long sys_chroot(const char __user * filename)
         if (error)
                 goto out;
 
-        error = permission(nd.dentry->d_inode,MAY_EXEC,&nd);
+        error = vfs_permission(&nd, MAY_EXEC);
         if (error)
                 goto dput_and_out;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1b5f502a4b8f..c3b8c1dc7cdf 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -874,6 +874,7 @@ static inline void unlock_super(struct super_block * sb)
 /*
  * VFS helper functions..
  */
+extern int vfs_permission(struct nameidata *, int);
 extern int vfs_create(struct inode *, struct dentry *, int, struct nameidata *);
 extern int vfs_mkdir(struct inode *, struct dentry *, int);
 extern int vfs_mknod(struct inode *, struct dentry *, int, dev_t);
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 41feca3bef86..acc73ba8bade 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -676,7 +676,7 @@ static struct sock *unix_find_other(struct sockaddr_un *sunname, int len,
                 err = path_lookup(sunname->sun_path, LOOKUP_FOLLOW, &nd);
                 if (err)
                         goto fail;
-                err = permission(nd.dentry->d_inode,MAY_WRITE, &nd);
+                err = vfs_permission(&nd, MAY_WRITE);
                 if (err)
                         goto put_fail;