New AT_... flag: AT_EMPTY_PATH

For name_to_handle_at(2) we'll want both ...at()-style syscall that
would be usable for non-directory descriptors (with empty relative
pathname).  Introduce new flag (AT_EMPTY_PATH) to deal with that and
corresponding LOOKUP_EMPTY; teach user_path_at() and path_init() to
deal with the latter.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 19 insertions, 10 deletions

diff --git a/fs/namei.c b/fs/namei.c
index abc8d2df121c..83e92bab79a6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -136,7 +136,7 @@ static int do_getname(const char __user *filename, char *page)
         return retval;
 }
 
-char * getname(const char __user * filename)
+static char *getname_flags(const char __user * filename, int flags)
 {
         char *tmp, *result;
 
@@ -147,14 +147,21 @@ char * getname(const char __user * filename)
 
                 result = tmp;
                 if (retval < 0) {
-                        __putname(tmp);
-                        result = ERR_PTR(retval);
+                        if (retval != -ENOENT || !(flags & LOOKUP_EMPTY)) {
+                                __putname(tmp);
+                                result = ERR_PTR(retval);
+                        }
                 }
         }
         audit_getname(result);
         return result;
 }
 
+char *getname(const char __user * filename)
+{
+        return getname_flags(filename, 0);
+}
+
 #ifdef CONFIG_AUDITSYSCALL
 void putname(const char *name)
 {
@@ -1544,13 +1551,15 @@ static int path_init(int dfd, const char *name, unsigned int flags,
 
                 dentry = file->f_path.dentry;
 
-                retval = -ENOTDIR;
-                if (!S_ISDIR(dentry->d_inode->i_mode))
-                        goto fput_fail;
+                if (*name) {
+                        retval = -ENOTDIR;
+                        if (!S_ISDIR(dentry->d_inode->i_mode))
+                                goto fput_fail;
 
-                retval = file_permission(file, MAY_EXEC);
-                if (retval)
-                        goto fput_fail;
+                        retval = file_permission(file, MAY_EXEC);
+                        if (retval)
+                                goto fput_fail;
+                }
 
                 nd->path = file->f_path;
                 if (flags & LOOKUP_RCU) {
@@ -1759,7 +1768,7 @@ int user_path_at(int dfd, const char __user *name, unsigned flags,
                  struct path *path)
 {
         struct nameidata nd;
-        char *tmp = getname(name);
+        char *tmp = getname_flags(name, flags);
         int err = PTR_ERR(tmp);
         if (!IS_ERR(tmp)) {