From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Ralph Boehme <slow@samba.org>,
	Steve French <stfrench@microsoft.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 1243/1250] smb/client: fix security flag calculation when setting security descriptors
Date: Thu, 17 Sep 2026 16:17:18 +0100
Message-ID: <20260917151625.986467835@linuxfoundation.org>
In-Reply-To: <20260917151551.901433442@linuxfoundation.org>
References: <20260917151551.901433442@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/smb/client/cifsacl.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

--- a/fs/smb/client/cifsacl.c
+++ b/fs/smb/client/cifsacl.c
@@ -1130,7 +1130,8 @@ set_size:
 
 static __u16 replace_sids_and_copy_aces(struct smb_acl *pdacl, struct smb_acl *pndacl,
 		struct smb_sid *pownersid, struct smb_sid *pgrpsid,
-		struct smb_sid *pnownersid, struct smb_sid *pngrpsid)
+		struct smb_sid *pnownersid, struct smb_sid *pngrpsid,
+		int *aclflag)
 {
 	int i;
 	u16 size = 0;
@@ -1154,12 +1155,15 @@ static __u16 replace_sids_and_copy_aces(
 		pntace = (struct smb_ace *) (acl_base + size);
 		pnntace = (struct smb_ace *) (nacl_base + nsize);
 
-		if (pnownersid && compare_sids(&pntace->sid, pownersid) == 0)
+		if (pnownersid && compare_sids(&pntace->sid, pownersid) == 0) {
 			ace_size = cifs_copy_ace(pnntace, pntace, pnownersid);
-		else if (pngrpsid && compare_sids(&pntace->sid, pgrpsid) == 0)
+			*aclflag |= CIFS_ACL_DACL;
+		} else if (pngrpsid && compare_sids(&pntace->sid, pgrpsid) == 0) {
 			ace_size = cifs_copy_ace(pnntace, pntace, pngrpsid);
-		else
+			*aclflag |= CIFS_ACL_DACL;
+		} else {
 			ace_size = cifs_copy_ace(pnntace, pntace, NULL);
+		}
 
 		size += le16_to_cpu(pntace->size);
 		nsize += ace_size;
@@ -1481,7 +1485,8 @@ static int build_sec_desc(struct smb_nts
 			/* Replace ACEs for old owner with new one */
 			size = replace_sids_and_copy_aces(dacl_ptr, ndacl_ptr,
 					owner_sid_ptr, group_sid_ptr,
-					nowner_sid_ptr, ngroup_sid_ptr);
+					nowner_sid_ptr, ngroup_sid_ptr,
+					aclflag);
 			ndacl_ptr->size = cpu_to_le16(size);
 		}
 
@@ -1696,7 +1701,7 @@ id_mode_to_cifs_acl(struct inode *inode,
 			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;
@@ -1802,6 +1807,11 @@ id_mode_to_cifs_acl(struct inode *inode,
 	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;