[PATCH v2 2/3] smb/server: deny overwriting targets with non-POSIX opens

[ChenXiaoSong <chenxiaosong@chenxiaosong.com>]

From: ChenXiaoSong <chenxiaosong@kylinos.cn>

Reproducer:

  1. server: systemctl start ksmbd
  2. client: mount without `posix` option
     mount -t cifs //${server_ip}/export /mnt
  3. client: touch /mnt/file1 /mnt/file2
  4. client: C program: int fd = open("/mnt/file2", O_RDONLY);
  5. client: C program: rename("/mnt/file1", "/mnt/file2");
  6. client: C program: struct stat stbuf; fstat(fd, &stbuf);
                        stbuf.st_nlink is 1, should be 0

This patch fixes xfstests generic/035 when mounted without `posix` option.

Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
---
 fs/smb/server/vfs.c       | 13 +++++++++++++
 fs/smb/server/vfs_cache.c | 32 ++++++++++++++++++++++++++++++++
 fs/smb/server/vfs_cache.h |  1 +
 3 files changed, 46 insertions(+)

diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 16ef8d051b18..9102ab47a3aa 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -726,6 +726,19 @@ int ksmbd_vfs_rename(struct ksmbd_work *work, struct ksmbd_file *old_fp,
 		goto out3;
 	}
 
+	/*
+	 * See MS-FSA 2.1.5.15.12.
+	 * An overwrite rename must fail with STATUS_ACCESS_DENIED if the
+	 * existing target still has a non-POSIX open.
+	 */
+	if (!(flags & (RENAME_NOREPLACE | RENAME_EXCHANGE)) &&
+	    d_inode(rd.new_dentry) &&
+	    d_inode(rd.new_dentry) != d_inode(old_child) &&
+	    ksmbd_has_other_nonposix_open(rd.new_dentry)) {
+		err = -EACCES;
+		goto out3;
+	}
+
 	err = ksmbd_vfs_check_rename_share(work, old_path);
 	if (err)
 		goto out3;
diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c
index 028bc1b0f652..94b2b5e48d3d 100644
--- a/fs/smb/server/vfs_cache.c
+++ b/fs/smb/server/vfs_cache.c
@@ -1137,6 +1137,38 @@ struct ksmbd_file *ksmbd_lookup_fd_inode(struct dentry *dentry)
 	return NULL;
 }
 
+bool ksmbd_has_other_nonposix_open(struct dentry *dentry)
+{
+	struct ksmbd_file *fp;
+	struct ksmbd_inode *ci;
+	struct inode *inode = d_inode(dentry);
+	bool ret = false;
+
+	if (!inode)
+		return false;
+
+	ci = ksmbd_inode_lookup_lock(dentry);
+	if (!ci)
+		return false;
+
+	down_read(&ci->m_lock);
+	list_for_each_entry(fp, &ci->m_fp_list, node) {
+		if (READ_ONCE(fp->f_state) != FP_INITED)
+			continue;
+		if (inode != file_inode(fp->filp))
+			continue;
+		if (fp->is_posix_ctxt)
+			continue;
+
+		ret = true;
+		break;
+	}
+	up_read(&ci->m_lock);
+	ksmbd_inode_put(ci);
+
+	return ret;
+}
+
 bool ksmbd_has_nonposix_open_child(struct ksmbd_file *old_fp)
 {
 	struct dentry *dentry = old_fp->filp->f_path.dentry;
diff --git a/fs/smb/server/vfs_cache.h b/fs/smb/server/vfs_cache.h
index 9dca617bc429..5cac022b540b 100644
--- a/fs/smb/server/vfs_cache.h
+++ b/fs/smb/server/vfs_cache.h
@@ -212,6 +212,7 @@ bool ksmbd_has_stream_without_delete_share(struct ksmbd_file *fp);
 int ksmbd_close_fd_app_instance_id(char *app_instance_id);
 struct ksmbd_file *ksmbd_lookup_fd_cguid(char *cguid);
 struct ksmbd_file *ksmbd_lookup_fd_inode(struct dentry *dentry);
+bool ksmbd_has_other_nonposix_open(struct dentry *dentry);
 bool ksmbd_has_nonposix_open_child(struct ksmbd_file *old_fp);
 unsigned int ksmbd_open_durable_fd(struct ksmbd_file *fp);
 struct ksmbd_file *ksmbd_open_fd(struct ksmbd_work *work, struct file *filp);
-- 
2.54.0