[PATCH 11/11] ksmbd: defer notify_change() call

From: Christian Brauner <brauner@kernel.org>
To: Steve French <stfrench@microsoft.com>,
	Christoph Hellwig <hch@infradead.org>,
	Namjae Jeon <namjae.jeon@samsung.com>,
	linux-cifs@vger.kernel.org
Cc: Hyunchul Lee <hyc.lee@gmail.com>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH 11/11] ksmbd: defer notify_change() call
Date: Mon, 23 Aug 2021 17:13:57 +0200	[thread overview]
Message-ID: <20210823151357.471691-12-brauner@kernel.org> (raw)
In-Reply-To: <20210823151357.471691-1-brauner@kernel.org>

From: Christian Brauner <christian.brauner@ubuntu.com>

When ownership is changed we might in certain scenarios loose the
ability to alter the inode after we changed ownership. This can e.g.
happen when we are on an idmapped mount where uid 0 is mapped to uid
1000 and uid 1000 is mapped to uid 0.
A caller with fs*id 1000 will be able to create files as *id 1000 on
disk. They will also be able to change ownership of files owned by *id 0
to *id 1000 but they won't be able to change ownership in the other
direction. This means acl operations following notify_change() would
fail. Move the notify_change() call after the acls have been updated.
This guarantees that we don't end up with spurious "hash value diff"
warnings later on because we managed to change ownership but didn't
manage to alter acls.

Cc: Steve French <stfrench@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/ksmbd/smbacl.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/ksmbd/smbacl.c b/fs/ksmbd/smbacl.c
index ef5896297607..8457a3c27c12 100644
--- a/fs/ksmbd/smbacl.c
+++ b/fs/ksmbd/smbacl.c
@@ -1334,25 +1334,27 @@ int set_info_sec(struct ksmbd_conn *conn, struct ksmbd_tree_connect *tcon,
 	newattrs.ia_valid |= ATTR_MODE;
 	newattrs.ia_mode = (inode->i_mode & ~0777) | (fattr.cf_mode & 0777);
 
-	inode_lock(inode);
-	rc = notify_change(user_ns, path->dentry, &newattrs, NULL);
-	inode_unlock(inode);
-	if (rc)
-		goto out;
-
 	ksmbd_vfs_remove_acl_xattrs(user_ns, path->dentry);
 	/* Update posix acls */
 	if (IS_ENABLED(CONFIG_FS_POSIX_ACL) && fattr.cf_dacls) {
 		rc = set_posix_acl(user_ns, inode,
 				   ACL_TYPE_ACCESS, fattr.cf_acls);
+		if (rc < 0)
+			ksmbd_debug(SMB,
+				    "Set posix acl(ACL_TYPE_ACCESS) failed, rc : %d\n",
+				    rc);
 		if (S_ISDIR(inode->i_mode) && fattr.cf_dacls)
 			rc = set_posix_acl(user_ns, inode,
 					   ACL_TYPE_DEFAULT, fattr.cf_dacls);
+		if (rc)
+			ksmbd_debug(SMB,
+				    "Set posix acl(ACL_TYPE_DEFAULT) failed, rc : %d\n",
+				    rc);
 	}
 
 	/* Check it only calling from SD BUFFER context */
 	if (type_check && !(le16_to_cpu(pntsd->type) & DACL_PRESENT))
-		goto out;
+		goto out_change;
 
 	if (test_share_config_flag(tcon->share_conf, KSMBD_SHARE_FLAG_ACL_XATTR)) {
 		/* Update WinACL in xattr */
@@ -1361,6 +1363,11 @@ int set_info_sec(struct ksmbd_conn *conn, struct ksmbd_tree_connect *tcon,
 				       path->dentry, pntsd, ntsd_len);
 	}
 
+out_change:
+	inode_lock(inode);
+	rc = notify_change(user_ns, path->dentry, &newattrs, NULL);
+	inode_unlock(inode);
+
 out:
 	posix_acl_release(fattr.cf_acls);
 	posix_acl_release(fattr.cf_dacls);
-- 
2.30.2

