fs: Provide function telling whether file_remove_privs() will do anything

Provide function telling whether file_remove_privs() will do anything.
Currently we only have should_remove_suid() and that does something
slightly different.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 33 insertions, 12 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 849210c155dc..8c2dd74455c9 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1673,7 +1673,32 @@ int should_remove_suid(struct dentry *dentry)
 }
 EXPORT_SYMBOL(should_remove_suid);
 
-static int __remove_suid(struct dentry *dentry, int kill)
+/*
+ * Return mask of changes for notify_change() that need to be done as a
+ * response to write or truncate. Return 0 if nothing has to be changed.
+ * Negative value on error (change should be denied).
+ */
+int file_needs_remove_privs(struct file *file)
+{
+        struct dentry *dentry = file->f_path.dentry;
+        struct inode *inode = d_inode(dentry);
+        int mask = 0;
+        int ret;
+
+        if (IS_NOSEC(inode))
+                return 0;
+
+        mask = should_remove_suid(dentry);
+        ret = security_inode_need_killpriv(dentry);
+        if (ret < 0)
+                return ret;
+        if (ret)
+                mask |= ATTR_KILL_PRIV;
+        return mask;
+}
+EXPORT_SYMBOL(file_needs_remove_privs);
+
+static int __remove_privs(struct dentry *dentry, int kill)
 {
         struct iattr newattrs;
 
@@ -1693,23 +1718,18 @@ int file_remove_privs(struct file *file)
 {
         struct dentry *dentry = file->f_path.dentry;
         struct inode *inode = d_inode(dentry);
-        int killsuid;
-        int killpriv;
+        int kill;
         int error = 0;
 
         /* Fast path for nothing security related */
         if (IS_NOSEC(inode))
                 return 0;
 
-        killsuid = should_remove_suid(dentry);
-        killpriv = security_inode_need_killpriv(dentry);
-
-        if (killpriv < 0)
-                return killpriv;
-        if (killpriv)
-                error = security_inode_killpriv(dentry);
-        if (!error && killsuid)
-                error = __remove_suid(dentry, killsuid);
+        kill = file_needs_remove_privs(file);
+        if (kill < 0)
+                return kill;
+        if (kill)
+                error = __remove_privs(dentry, kill);
         if (!error)
                 inode_has_no_xattr(inode);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 641e68d850cf..ee60e8ab210f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2554,6 +2554,7 @@ extern struct inode *new_inode(struct super_block *sb);
 extern void free_inode_nonrcu(struct inode *inode);
 extern int should_remove_suid(struct dentry *);
 extern int file_remove_privs(struct file *);
+extern int file_needs_remove_privs(struct file *file);
 
 extern void __insert_inode_hash(struct inode *, unsigned long hashval);
 static inline void insert_inode_hash(struct inode *inode)