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23bc760ec5
When using vfs_streams_xattr, for a pathref handle of a stream the system fd
will be a fake fd created by pipe() in vfs_fake_fd().
For the following callchain we wrongly pass a stream fsp to
SMB_VFS_FGET_NT_ACL():
SMB_VFS_CREATE_FILE(..., "file:stream", ...)
=> open_file():
if (open_fd):
-> taking the else branch:
-> smbd_check_access_rights_fsp(stream_fsp)
-> SMB_VFS_FGET_NT_ACL(stream_fsp)
This is obviously wrong and can lead to strange permission errors when using
vfs_acl_xattr:
in vfs_acl_xattr we will try to read the stored ACL by calling
fgetxattr(fake-fd) which of course faild with EBADF. Now unfortunately the
vfs_acl_xattr code ignores the specific error and handles this as if there was
no ACL stored and subsequently runs the code to synthesize a default ACL
according to the setting of "acl:default acl style".
As the correct access check for streams has already been carried out by calling
check_base_file_access() from create_file_unixpath(), the above problem is not
a security issue: it can only lead to "decreased" permissions resulting in
unexpected ACCESS_DENIED errors.
The fix is obviously going to be calling
smbd_check_access_rights_fsp(stream_fsp->base_fsp).
This test verifies that deleting a file works when the stored NT ACL grants
DELETE_FILE while the basic POSIX permissions (used in the acl_xattr fallback
code) do not.
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15126
MR: https://gitlab.com/samba-team/samba/-/merge_requests/2643
Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>