ext4: Don't clear SGID when inheriting ACLs

BugLink: http://bugs.launchpad.net/bugs/1724783

commit a3bb2d55 upstream.

When new directory 'DIR1' is created in a directory 'DIR0' with SGID bit
set, DIR1 is expected to have SGID bit set (and owning group equal to
the owning group of 'DIR0'). However when 'DIR0' also has some default
ACLs that 'DIR1' inherits, setting these ACLs will result in SGID bit on
'DIR1' to get cleared if user is not member of the owning group.

Fix the problem by moving posix_acl_update_mode() out of
__ext4_set_acl() into ext4_set_acl(). That way the function will not be
called when inheriting ACLs which is what we want as it prevents SGID
bit clearing and the mode has been properly set by posix_acl_create()
anyway.

Fixes: 07393101Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

fs/ext4/acl.c

@@ -206,13 +206,6 @@ __ext4_set_acl(handle_t *handle, struct inode *inode, int type,
 	switch (type) {
 	case ACL_TYPE_ACCESS:
 		name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS;
-		if (acl) {
-			error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
-			if (error)
-				return error;
-			inode->i_ctime = ext4_current_time(inode);
-			ext4_mark_inode_dirty(handle, inode);
-		}
 		break;
 
 	case ACL_TYPE_DEFAULT:
@@ -245,6 +238,8 @@ ext4_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 {
 	handle_t *handle;
 	int error, retries = 0;
+	umode_t mode = inode->i_mode;
+	int update_mode = 0;
 
 retry:
 	handle = ext4_journal_start(inode, EXT4_HT_XATTR,
@@ -252,7 +247,20 @@ ext4_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);
 
+	if ((type == ACL_TYPE_ACCESS) && acl) {
+		error = posix_acl_update_mode(inode, &mode, &acl);
+		if (error)
+			goto out_stop;
+		update_mode = 1;
+	}
+
 	error = __ext4_set_acl(handle, inode, type, acl);
+	if (!error && update_mode) {
+		inode->i_mode = mode;
+		inode->i_ctime = ext4_current_time(inode);
+		ext4_mark_inode_dirty(handle, inode);
+	}
+out_stop:
 	ext4_journal_stop(handle);
 	if (error == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
 		goto retry;