[CIFS] CIFS currently allows for permissions to be changed on files, even

when unix extensions and cifsacl support are disabled. These
permissions changes are "ephemeral" however. They are lost whenever
a share is mounted and unmounted, or when memory pressure forces
the inode out of the cache.

Because of this, we'd like to introduce a behavior change to make
CIFS behave more like local DOS/Windows filesystems. When unix
extensions and cifsacl support aren't enabled, then don't silently
ignore changes to permission bits that can't be reflected on the
server.

Still, there may be people relying on the current behavior for
certain applications. This patch adds a new "dynperm" (and a
corresponding "nodynperm") mount option that will be intended
to make the client fall back to legacy behavior when setting
these modes.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifs_fs_sb.h

@@ -30,6 +30,7 @@
 #define CIFS_MOUNT_CIFS_ACL     0x200 /* send ACL requests to non-POSIX srv   */
 #define CIFS_MOUNT_OVERR_UID    0x400 /* override uid returned from server    */
 #define CIFS_MOUNT_OVERR_GID    0x800 /* override gid returned from server    */
+#define CIFS_MOUNT_DYNPERM	0x1000 /* allow in-memory only mode setting */
 
 struct cifs_sb_info {
 	struct cifsTconInfo *tcon;	/* primary mount */

fs/cifs/connect.c

@@ -75,6 +75,7 @@ struct smb_vol {
 	bool setuids:1;
 	bool override_uid:1;
 	bool override_gid:1;
+	bool dynperm:1;
 	bool noperm:1;
 	bool no_psx_acl:1; /* set if posix acl support should be disabled */
 	bool cifs_acl:1;
@@ -1246,6 +1247,10 @@ cifs_parse_mount_options(char *options, const char *devname,
 			vol->setuids = 1;
 		} else if (strnicmp(data, "nosetuids", 9) == 0) {
 			vol->setuids = 0;
+		} else if (strnicmp(data, "dynperm", 7) == 0) {
+			vol->dynperm = true;
+		} else if (strnicmp(data, "nodynperm", 9) == 0) {
+			vol->dynperm = false;
 		} else if (strnicmp(data, "nohard", 6) == 0) {
 			vol->retry = 0;
 		} else if (strnicmp(data, "nosoft", 6) == 0) {
@@ -2125,6 +2130,8 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
 			cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_OVERR_UID;
 		if (volume_info.override_gid)
 			cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_OVERR_GID;
+		if (volume_info.dynperm)
+			cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_DYNPERM;
 		if (volume_info.direct_io) {
 			cFYI(1, ("mounting share using direct i/o"));
 			cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_DIRECT_IO;