[PATCH 5.15.y 3/4] smb/client: fix security flag calculation when setting security descriptors

[Sasha Levin <sashal@kernel.org>]

From: Ralph Boehme <slow@samba.org>

[ Upstream commit 4939889c985da68936090cc013e58c28b7bff34f ]

In id_mode_to_cifs_acl(), aclflag was initialized to CIFS_ACL_DACL by default.
This forced the client to request setting the DACL even when only an ownership
(chown) or group (chgrp) change was being performed.

Let build_sec_desc() do the proper flag calculation by initializing aclflag
to 0. build_sec_desc() sets the appropriate bits (CIFS_ACL_OWNER, CIFS_ACL_GROUP,
or CIFS_ACL_DACL) depending on what actually changed. During ownership transfer,
CIFS_ACL_DACL is only set if replace_sids_and_copy_aces() actually replaces the
SIDs inside any of the DACL's ACEs.

If build_sec_desc() results in aclflag being 0 (meaning no changes were mapped),
exit early to avoid sending an empty security descriptor update to the server.

Signed-off-by: Ralph Boehme <slow@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Stable-dep-of: d05045177a85 ("smb: client: fail DACL rewrite when the new DACL exceeds 64K")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/cifs/cifsacl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
index 4e7ac1c4e5af0..03be080dfd480 100644
--- a/fs/cifs/cifsacl.c
+++ b/fs/cifs/cifsacl.c
@@ -1674,7 +1674,7 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 			kuid_t uid, kgid_t gid)
 {
 	int rc = 0;
-	int aclflag = CIFS_ACL_DACL; /* default flag to set */
+	int aclflag = 0;
 	__u32 secdesclen = 0;
 	__u32 nsecdesclen = 0;
 	__u32 dacloffset = 0;
@@ -1773,6 +1773,11 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode,
 	if (rc != 0)
 		goto id_mode_to_cifs_acl_exit;
 
+	if (aclflag == 0) {
+		cifs_dbg(FYI, "set_cifs_acl aclflag=0, no change mapped\n");
+		goto id_mode_to_cifs_acl_exit;
+	}
+
 	if (ops->set_acl == NULL) {
 		rc = -EOPNOTSUPP;
 		goto id_mode_to_cifs_acl_exit;
-- 
2.53.0