[PATCH 6/7] ksmbd: fix stale sparse-file attribute after share reconfiguration

From: Gael Blivet <[email protected]>

smb2_update_xattrs() copies the DOS SPARSE attribute bit verbatim from
the stored xattr into the in-memory file attributes, without checking
whether the share is currently advertising FILE_SUPPORTS_SPARSE_FILES.
A file whose xattr has a stale SPARSE bit (set by a previous client,
or from before the share was reconfigured) would keep reporting as
sparse even after sparse-file support is turned off for the share.
This matters for Time Machine: sparsebundle band files rely on
accurate sparse-file status being reported, since macOS decides
whether to issue FSCTL_SET_SPARSE based on it. Mask the bit out when
the share doesn't currently advertise sparse-file support.

Signed-off-by: Gael Blivet <[email protected]>
---
 fs/smb/server/smb2pdu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index af957d013..d5d88d023 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -2940,6 +2940,16 @@ static void smb2_update_xattrs(struct ksmbd_tree_connect *tcon,
 	rc = ksmbd_vfs_get_dos_attrib_xattr(mnt_idmap(path->mnt),
 					    path->dentry, &da);
 	if (rc > 0) {
+		/*
+		 * Don't report a stale SPARSE bit (e.g. left over from a
+		 * previous client, or from before the share was reconfigured)
+		 * when the share isn't currently advertising sparse-file
+		 * support. Time Machine sparsebundle band files rely on
+		 * sparse status being accurate, since macOS decides whether
+		 * to use FSCTL_SET_SPARSE based on it.
+		 */
+		if (!(server_conf.share_fake_fscaps & FILE_SUPPORTS_SPARSE_FILES))
+			da.attr &= ~FILE_ATTRIBUTE_SPARSE_FILE;
 		fp->f_ci->m_fattr = cpu_to_le32(da.attr);
 		fp->create_time = da.create_time;
 		fp->itime = da.itime;
-- 
2.43.0