ksmbd: enforce the read-only share flag when creating a stream

When a share is read-only, smb2_open() rejects opens that would create
or truncate a file. Creating a named stream on an existing file with
streams_xattr sets neither O_CREAT nor O_TRUNC, so it passes this check,
and smb2_set_stream_name_xattr() then creates the stream. On a Time
Machine share, opening a missing AFP_AfpInfo stream also writes one. A
user who can write a file at the filesystem level can therefore add
streams to it through a read-only share.

Do not create a stream or synthesize AFP_AfpInfo when the share is not
writable. Existing streams still open normally, and a missing stream
opened with FILE_OPEN still returns STATUS_OBJECT_NAME_NOT_FOUND.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Fixes: eaff8e924f60 ("ksmbd: synthesize empty AFP_AfpInfo xattr on first probe")
Cc: stable@vger.kernel.org
Signed-off-by: Ian Bridges <icb@fastmail.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions