Fwd: [SMB3][PATCH] add mount option to allow retrieving POSIX mode from special ACE

Fwd: [SMB3][PATCH] add mount option to allow retrieving POSIX mode from special ACE

[L A Walsh]

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I was wondering if this would be something cygwin could use for storing
the mode bits.  If I understand the usage, it would have the advantage
of being
compatible with with samba storage of mode bits and storage of
POSIX-mode bits
in a Windows ACL.



-------- Original Message --------
Subject: 	[SMB3][PATCH] add mount option to allow retrieving POSIX mode
from special ACE
Date: 	Mon, 24 Jun 2019 02:11:57 -0500
From: 	Steve French <smfrench@gmail.com>
To: 	CIFS <linux-cifs@vger.kernel.org>



See e.g. https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/hh509017(v=ws.10)

where it describes use of an ACE with special SID S-1-5-88-3 to store the mode.

Followon patches will add the support for chmod and query_info (stat)



-- 
Thanks,

Steve



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From 952f30b31c903f8f6f4ca023061c108d16cc6df6 Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Mon, 24 Jun 2019 02:01:42 -0500
Subject: [PATCH] smb3: add new mount option to retrieve mode from special ACE

There is a special ACE used by some servers to allow the mode
bits to be stored.  This can be especially helpful in scenarios
in which the client is trusted, and access checking on the
client vs the POSIX mode bits is sufficient.

Add mount option to allow enabling this behavior.
Follow on patch will add the support to add chmod and queryinfo
(stat) support for retrieving the POSIX mode bits from the
special ACE, SID: S-1-5-88-3

See e.g.
https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/hh509017(v=ws.10)

Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/cifs_fs_sb.h | 1 +
 fs/cifs/cifsfs.c     | 2 ++
 fs/cifs/cifsglob.h   | 2 +-
 fs/cifs/connect.c    | 6 ++++++
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
index afa56237a0c3..744e48bdcb6c 100644
--- a/fs/cifs/cifs_fs_sb.h
+++ b/fs/cifs/cifs_fs_sb.h
@@ -52,6 +52,7 @@
 #define CIFS_MOUNT_UID_FROM_ACL 0x2000000 /* try to get UID via special SID */
 #define CIFS_MOUNT_NO_HANDLE_CACHE 0x4000000 /* disable caching dir handles */
 #define CIFS_MOUNT_NO_DFS 0x8000000 /* disable DFS resolving */
+#define CIFS_MOUNT_MODE_FROM_ACE 0x10000000 /* retrieve mode from special ACE */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index dc5fd7a648f0..e33da73bd300 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -526,6 +526,8 @@ cifs_show_options(struct seq_file *s, struct dentry *root)
 		seq_puts(s, ",nobrl");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_HANDLE_CACHE)
 		seq_puts(s, ",nohandlecache");
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MODE_FROM_ACE)
+		seq_puts(s, ",modefromace");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL)
 		seq_puts(s, ",cifsacl");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_DYNPERM)
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 16f240911192..2c87547e42ab 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -618,7 +618,7 @@ struct smb_vol {
 			 CIFS_MOUNT_MULTIUSER | CIFS_MOUNT_STRICT_IO | \
 			 CIFS_MOUNT_CIFS_BACKUPUID | CIFS_MOUNT_CIFS_BACKUPGID | \
 			 CIFS_MOUNT_UID_FROM_ACL | CIFS_MOUNT_NO_HANDLE_CACHE | \
-			 CIFS_MOUNT_NO_DFS)
+			 CIFS_MOUNT_NO_DFS | CIFS_MOUNT_MODE_FROM_ACE)
 
 /**
  * Generic VFS superblock mount flags (s_flags) to consider when
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index b8a60060d329..f7bc85775f96 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -175,6 +175,7 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_serverino, "serverino" },
 	{ Opt_noserverino, "noserverino" },
 	{ Opt_rwpidforward, "rwpidforward" },
+	{ Opt_modeace, "modefromace" },
 	{ Opt_cifsacl, "cifsacl" },
 	{ Opt_nocifsacl, "nocifsacl" },
 	{ Opt_acl, "acl" },
@@ -1830,6 +1831,9 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 		case Opt_rwpidforward:
 			vol->rwpidforward = 1;
 			break;
+		case Opt_modeace:
+			vol->mode_ace = 1;
+			break;
 		case Opt_cifsacl:
 			vol->cifs_acl = 1;
 			break;
@@ -3976,6 +3980,8 @@ int cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NOPOSIXBRL;
 	if (pvolume_info->rwpidforward)
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_RWPIDFORWARD;
+	if (pvolume_info->mode_ace)
+		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_MODE_FROM_ACE;
 	if (pvolume_info->cifs_acl)
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_CIFS_ACL;
 	if (pvolume_info->backupuid_specified) {
-- 
2.20.1


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