1 files changed, 29 insertions, 0 deletions
diff --git a/fs/attr.c b/fs/attr.c
index b1162fca84a2..e508b3caae76 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -20,6 +20,35 @@
 
 #include "internal.h"
 
+/*
+ * The logic we want is
+ *
+ *	if suid or (sgid and xgrp)
+ *		remove privs
+ */
+int should_remove_suid(struct dentry *dentry)
+{
+	umode_t mode = d_inode(dentry)->i_mode;
+	int kill = 0;
+
+	/* suid always must be killed */
+	if (unlikely(mode & S_ISUID))
+		kill = ATTR_KILL_SUID;
+
+	/*
+	 * sgid without any exec bits is just a mandatory locking mark; leave
+	 * it alone.  If some exec bits are set, it's a real sgid; kill it.
+	 */
+	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
+		kill |= ATTR_KILL_SGID;
+
+	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
+		return kill;
+
+	return 0;
+}
+EXPORT_SYMBOL(should_remove_suid);
+
 /**
  * chown_ok - verify permissions to chown inode
  * @mnt_userns:	user namespace of the mount @inode was found from