1 files changed, 68 insertions, 6 deletions

diff --git a/fs/attr.c b/fs/attr.c
index 1552a5f23d6b..b45f30e516fa 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -18,6 +18,70 @@
 #include <linux/evm.h>
 #include <linux/ima.h>
 
+#include "internal.h"
+
+/**
+ * setattr_should_drop_sgid - determine whether the setgid bit needs to be
+ *                            removed
+ * @mnt_userns:	user namespace of the mount @inode was found from
+ * @inode:	inode to check
+ *
+ * This function determines whether the setgid bit needs to be removed.
+ * We retain backwards compatibility and require setgid bit to be removed
+ * unconditionally if S_IXGRP is set. Otherwise we have the exact same
+ * requirements as setattr_prepare() and setattr_copy().
+ *
+ * Return: ATTR_KILL_SGID if setgid bit needs to be removed, 0 otherwise.
+ */
+int setattr_should_drop_sgid(struct user_namespace *mnt_userns,
+			     const struct inode *inode)
+{
+	umode_t mode = inode->i_mode;
+
+	if (!(mode & S_ISGID))
+		return 0;
+	if (mode & S_IXGRP)
+		return ATTR_KILL_SGID;
+	if (!in_group_or_capable(mnt_userns, inode,
+				 i_gid_into_vfsgid(mnt_userns, inode)))
+		return ATTR_KILL_SGID;
+	return 0;
+}
+
+/**
+ * setattr_should_drop_suidgid - determine whether the set{g,u}id bit needs to
+ *                               be dropped
+ * @mnt_userns:	user namespace of the mount @inode was found from
+ * @inode:	inode to check
+ *
+ * This function determines whether the set{g,u}id bits need to be removed.
+ * If the setuid bit needs to be removed ATTR_KILL_SUID is returned. If the
+ * setgid bit needs to be removed ATTR_KILL_SGID is returned. If both
+ * set{g,u}id bits need to be removed the corresponding mask of both flags is
+ * returned.
+ *
+ * Return: A mask of ATTR_KILL_S{G,U}ID indicating which - if any - setid bits
+ * to remove, 0 otherwise.
+ */
+int setattr_should_drop_suidgid(struct user_namespace *mnt_userns,
+				struct inode *inode)
+{
+	umode_t mode = inode->i_mode;
+	int kill = 0;
+
+	/* suid always must be killed */
+	if (unlikely(mode & S_ISUID))
+		kill = ATTR_KILL_SUID;
+
+	kill |= setattr_should_drop_sgid(mnt_userns, inode);
+
+	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
+		return kill;
+
+	return 0;
+}
+EXPORT_SYMBOL(setattr_should_drop_suidgid);
+
 /**
  * chown_ok - verify permissions to chown inode
  * @mnt_userns:	user namespace of the mount @inode was found from
@@ -140,8 +204,7 @@ int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
 			vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
 
 		/* Also check the setgid bit! */
-		if (!vfsgid_in_group_p(vfsgid) &&
-		    !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+		if (!in_group_or_capable(mnt_userns, inode, vfsgid))
 			attr->ia_mode &= ~S_ISGID;
 	}
 
@@ -251,9 +314,8 @@ void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode,
 		inode->i_ctime = attr->ia_ctime;
 	if (ia_valid & ATTR_MODE) {
 		umode_t mode = attr->ia_mode;
-		vfsgid_t vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
-		if (!vfsgid_in_group_p(vfsgid) &&
-		    !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+		if (!in_group_or_capable(mnt_userns, inode,
+					 i_gid_into_vfsgid(mnt_userns, inode)))
 			mode &= ~S_ISGID;
 		inode->i_mode = mode;
 	}
@@ -375,7 +437,7 @@ int notify_change(struct user_namespace *mnt_userns, struct dentry *dentry,
 		}
 	}
 	if (ia_valid & ATTR_KILL_SGID) {
-		if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
+		if (mode & S_ISGID) {
 			if (!(ia_valid & ATTR_MODE)) {
 				ia_valid = attr->ia_valid |= ATTR_MODE;
 				attr->ia_mode = inode->i_mode;