fs: namespace: suppress 'may be used uninitialized' warnings

The gcc version 4.9.1 compiler complains Even though it isn't possible for
these variables to not get initialized before they are used.

fs/namespace.c: In function ‘SyS_mount’:
fs/namespace.c:2720:8: warning: ‘kernel_dev’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags,
        ^
fs/namespace.c:2699:8: note: ‘kernel_dev’ was declared here
  char *kernel_dev;
        ^
fs/namespace.c:2720:8: warning: ‘kernel_type’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags,
        ^
fs/namespace.c:2697:8: note: ‘kernel_type’ was declared here
  char *kernel_type;
        ^

Fix the warnings by simplifying copy_mount_string() as suggested by Al Viro.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 15 insertions, 23 deletions

diff --git a/fs/compat.c b/fs/compat.c
index 66d3d3c6b4b2..6205c247a6e3 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -797,8 +797,9 @@ COMPAT_SYSCALL_DEFINE5(mount, const char __user *, dev_name,
         struct filename *dir;
         int retval;
 
-        retval = copy_mount_string(type, &kernel_type);
-        if (retval < 0)
+        kernel_type = copy_mount_string(type);
+        retval = PTR_ERR(kernel_type);
+        if (IS_ERR(kernel_type))
                 goto out;
 
         dir = getname(dir_name);
@@ -806,8 +807,9 @@ COMPAT_SYSCALL_DEFINE5(mount, const char __user *, dev_name,
         if (IS_ERR(dir))
                 goto out1;
 
-        retval = copy_mount_string(dev_name, &kernel_dev);
-        if (retval < 0)
+        kernel_dev = copy_mount_string(dev_name);
+        retval = PTR_ERR(kernel_dev);
+        if (IS_ERR(kernel_dev))
                 goto out2;
 
         retval = copy_mount_options(data, &data_page);
diff --git a/fs/internal.h b/fs/internal.h
index e325b4f9c799..bd4ac19f4d8f 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -51,7 +51,7 @@ extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
  * namespace.c
  */
 extern int copy_mount_options(const void __user *, unsigned long *);
-extern int copy_mount_string(const void __user *, char **);
+extern char *copy_mount_string(const void __user *);
 
 extern struct vfsmount *lookup_mnt(struct path *);
 extern int finish_automount(struct vfsmount *, struct path *);
diff --git a/fs/namespace.c b/fs/namespace.c
index 00e5b1efa591..abd3abb52616 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2514,21 +2514,9 @@ int copy_mount_options(const void __user * data, unsigned long *where)
         return 0;
 }
 
-int copy_mount_string(const void __user *data, char **where)
+char *copy_mount_string(const void __user *data)
 {
-        char *tmp;
-
-        if (!data) {
-                *where = NULL;
-                return 0;
-        }
-
-        tmp = strndup_user(data, PAGE_SIZE);
-        if (IS_ERR(tmp))
-                return PTR_ERR(tmp);
-
-        *where = tmp;
-        return 0;
+        return data ? strndup_user(data, PAGE_SIZE) : NULL;
 }
 
 /*
@@ -2794,8 +2782,9 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
         char *kernel_dev;
         unsigned long data_page;
 
-        ret = copy_mount_string(type, &kernel_type);
-        if (ret < 0)
+        kernel_type = copy_mount_string(type);
+        ret = PTR_ERR(kernel_type);
+        if (IS_ERR(kernel_type))
                 goto out_type;
 
         kernel_dir = getname(dir_name);
@@ -2804,8 +2793,9 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
                 goto out_dir;
         }
 
-        ret = copy_mount_string(dev_name, &kernel_dev);
-        if (ret < 0)
+        kernel_dev = copy_mount_string(dev_name);
+        ret = PTR_ERR(kernel_dev);
+        if (IS_ERR(kernel_dev))
                 goto out_dev;
 
         ret = copy_mount_options(data, &data_page);