cifs: Add data structures and functions for uid/gid to SID mapping (try #4)

Add data structures and functions necessary to map a uid and gid to SID.
These functions are very similar to the ones used to map a SID to uid and gid.
This time, instead of storing sid to id mapping sorted on a sid value,
id to sid is stored, sorted on an id.
A cifs upcall sends an id (uid or gid) and expects a SID structure
in return, if mapping was done successfully.

A failed id to sid mapping to EINVAL.

This patchset aims to enable chown and chgrp commands when
cifsacl mount option is specified, especially to Windows SMB servers.
Currently we can't do that.  So now along with chmod command,
chown and chgrp work.

Winbind is used to map id to a SID.  chown and chgrp use an upcall
to provide an id to winbind and upcall returns with corrosponding
SID if any exists. That SID is used to build security descriptor.
The DACL part of a security descriptor is not changed by either
chown or chgrp functionality.

cifs client maintains a separate caches for uid to SID and
gid to SID mapping. This is similar to the one used earlier
to map SID to id (as part of ID mapping code).

I tested it by mounting shares from a Windows (2003) server by
authenticating as two users, one at a time, as Administrator and
as a ordinary user.
And then attempting to change owner of a file on the share.

Depending on the permissions/privileges at the server for that file,
chown request fails to either open a file (to change the ownership)
or to set security descriptor.
So it all depends on privileges on the file at the server and what
user you are authenticated as at the server, cifs client is just a
conduit.

I compared the security descriptor during chown command to that
what smbcacls sends when it is used with -M OWNNER: option
and they are similar.

This patchset aim to enable chown and chgrp commands when
cifsacl mount option is specified, especially to Windows SMB servers.
Currently we can't do that.  So now along with chmod command,
chown and chgrp work.

I tested it by mounting shares from a Windows (2003) server by
authenticating as two users, one at a time, as Administrator and
as a ordinary user.
And then attempting to change owner of a file on the share.

Depending on the permissions/privileges at the server for that file,
chown request fails to either open a file (to change the ownership)
or to set security descriptor.
So it all depends on privileges on the file at the server and what
user you are authenticated as at the server, cifs client is just a
conduit.

Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 198 insertions, 0 deletions

diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
index b244e07c304..992f1fb299d 100644
--- a/fs/cifs/cifsacl.c
+++ b/fs/cifs/cifsacl.c
@@ -91,9 +91,76 @@ cifs_idmap_shrinker(struct shrinker *shrink, struct shrink_control *sc)
 	shrink_idmap_tree(root, nr_to_scan, &nr_rem, &nr_del);
 	spin_unlock(&sidgidlock);
 
+	root = &siduidtree;
+	spin_lock(&uidsidlock);
+	shrink_idmap_tree(root, nr_to_scan, &nr_rem, &nr_del);
+	spin_unlock(&uidsidlock);
+
+	root = &sidgidtree;
+	spin_lock(&gidsidlock);
+	shrink_idmap_tree(root, nr_to_scan, &nr_rem, &nr_del);
+	spin_unlock(&gidsidlock);
+
 	return nr_rem;
 }
 
+static void
+sid_rb_insert(struct rb_root *root, unsigned long cid,
+		struct cifs_sid_id **psidid, char *typestr)
+{
+	char *strptr;
+	struct rb_node *node = root->rb_node;
+	struct rb_node *parent = NULL;
+	struct rb_node **linkto = &(root->rb_node);
+	struct cifs_sid_id *lsidid;
+
+	while (node) {
+		lsidid = rb_entry(node, struct cifs_sid_id, rbnode);
+		parent = node;
+		if (cid > lsidid->id) {
+			linkto = &(node->rb_left);
+			node = node->rb_left;
+		}
+		if (cid < lsidid->id) {
+			linkto = &(node->rb_right);
+			node = node->rb_right;
+		}
+	}
+
+	(*psidid)->id = cid;
+	(*psidid)->time = jiffies - (SID_MAP_RETRY + 1);
+	(*psidid)->refcount = 0;
+
+	sprintf((*psidid)->sidstr, "%s", typestr);
+	strptr = (*psidid)->sidstr + strlen((*psidid)->sidstr);
+	sprintf(strptr, "%ld", cid);
+
+	clear_bit(SID_ID_PENDING, &(*psidid)->state);
+	clear_bit(SID_ID_MAPPED, &(*psidid)->state);
+
+	rb_link_node(&(*psidid)->rbnode, parent, linkto);
+	rb_insert_color(&(*psidid)->rbnode, root);
+}
+
+static struct cifs_sid_id *
+sid_rb_search(struct rb_root *root, unsigned long cid)
+{
+	struct rb_node *node = root->rb_node;
+	struct cifs_sid_id *lsidid;
+
+	while (node) {
+		lsidid = rb_entry(node, struct cifs_sid_id, rbnode);
+		if (cid > lsidid->id)
+			node = node->rb_left;
+		else if (cid < lsidid->id)
+			node = node->rb_right;
+		else /* node found */
+			return lsidid;
+	}
+
+	return NULL;
+}
+
 static struct shrinker cifs_shrinker = {
 	.shrink = cifs_idmap_shrinker,
 	.seeks = DEFAULT_SEEKS,
@@ -110,6 +177,7 @@ cifs_idmap_key_instantiate(struct key *key, const void *data, size_t datalen)
 
 	memcpy(payload, data, datalen);
 	key->payload.data = payload;
+	key->datalen = datalen;
 	return 0;
 }
 
@@ -224,6 +292,120 @@ sidid_pending_wait(void *unused)
 }
 
 static int
+id_to_sid(unsigned long cid, uint sidtype, struct cifs_sid *ssid)
+{
+	int rc = 0;
+	struct key *sidkey;
+	const struct cred *saved_cred;
+	struct cifs_sid *lsid;
+	struct cifs_sid_id *psidid, *npsidid;
+	struct rb_root *cidtree;
+	spinlock_t *cidlock;
+
+	if (sidtype == SIDOWNER) {
+		cidlock = &siduidlock;
+		cidtree = &uidtree;
+	} else if (sidtype == SIDGROUP) {
+		cidlock = &sidgidlock;
+		cidtree = &gidtree;
+	} else
+		return -EINVAL;
+
+	spin_lock(cidlock);
+	psidid = sid_rb_search(cidtree, cid);
+
+	if (!psidid) { /* node does not exist, allocate one & attempt adding */
+		spin_unlock(cidlock);
+		npsidid = kzalloc(sizeof(struct cifs_sid_id), GFP_KERNEL);
+		if (!npsidid)
+			return -ENOMEM;
+
+		npsidid->sidstr = kmalloc(SIDLEN, GFP_KERNEL);
+		if (!npsidid->sidstr) {
+			kfree(npsidid);
+			return -ENOMEM;
+		}
+
+		spin_lock(cidlock);
+		psidid = sid_rb_search(cidtree, cid);
+		if (psidid) { /* node happened to get inserted meanwhile */
+			++psidid->refcount;
+			spin_unlock(cidlock);
+			kfree(npsidid->sidstr);
+			kfree(npsidid);
+		} else {
+			psidid = npsidid;
+			sid_rb_insert(cidtree, cid, &psidid,
+					sidtype == SIDOWNER ? "oi:" : "gi:");
+			++psidid->refcount;
+			spin_unlock(cidlock);
+		}
+	} else {
+		++psidid->refcount;
+		spin_unlock(cidlock);
+	}
+
+	/*
+	 * If we are here, it is safe to access psidid and its fields
+	 * since a reference was taken earlier while holding the spinlock.
+	 * A reference on the node is put without holding the spinlock
+	 * and it is OK to do so in this case, shrinker will not erase
+	 * this node until all references are put and we do not access
+	 * any fields of the node after a reference is put .
+	 */
+	if (test_bit(SID_ID_MAPPED, &psidid->state)) {
+		memcpy(ssid, &psidid->sid, sizeof(struct cifs_sid));
+		psidid->time = jiffies; /* update ts for accessing */
+		goto id_sid_out;
+	}
+
+	if (time_after(psidid->time + SID_MAP_RETRY, jiffies)) {
+		rc = -EINVAL;
+		goto id_sid_out;
+	}
+
+	if (!test_and_set_bit(SID_ID_PENDING, &psidid->state)) {
+		saved_cred = override_creds(root_cred);
+		sidkey = request_key(&cifs_idmap_key_type, psidid->sidstr, "");
+		if (IS_ERR(sidkey)) {
+			rc = -EINVAL;
+			cFYI(1, "%s: Can't map and id to a SID", __func__);
+		} else {
+			lsid = (struct cifs_sid *)sidkey->payload.data;
+			memcpy(&psidid->sid, lsid,
+				sidkey->datalen < sizeof(struct cifs_sid) ?
+				sidkey->datalen : sizeof(struct cifs_sid));
+			memcpy(ssid, &psidid->sid,
+				sidkey->datalen < sizeof(struct cifs_sid) ?
+				sidkey->datalen : sizeof(struct cifs_sid));
+			set_bit(SID_ID_MAPPED, &psidid->state);
+			key_put(sidkey);
+			kfree(psidid->sidstr);
+		}
+		psidid->time = jiffies; /* update ts for accessing */
+		revert_creds(saved_cred);
+		clear_bit(SID_ID_PENDING, &psidid->state);
+		wake_up_bit(&psidid->state, SID_ID_PENDING);
+	} else {
+		rc = wait_on_bit(&psidid->state, SID_ID_PENDING,
+				sidid_pending_wait, TASK_INTERRUPTIBLE);
+		if (rc) {
+			cFYI(1, "%s: sidid_pending_wait interrupted %d",
+					__func__, rc);
+			--psidid->refcount;
+			return rc;
+		}
+		if (test_bit(SID_ID_MAPPED, &psidid->state))
+			memcpy(ssid, &psidid->sid, sizeof(struct cifs_sid));
+		else
+			rc = -EINVAL;
+	}
+id_sid_out:
+	--psidid->refcount;
+	return rc;
+}
+
+static int
 sid_to_id(struct cifs_sb_info *cifs_sb, struct cifs_sid *psid,
 		struct cifs_fattr *fattr, uint sidtype)
 {
@@ -383,6 +565,10 @@ init_cifs_idmap(void)
 	spin_lock_init(&sidgidlock);
 	gidtree = RB_ROOT;
 
+	spin_lock_init(&uidsidlock);
+	siduidtree = RB_ROOT;
+	spin_lock_init(&gidsidlock);
+	sidgidtree = RB_ROOT;
 	register_shrinker(&cifs_shrinker);
 
 	cFYI(1, "cifs idmap keyring: %d\n", key_serial(keyring));
@@ -422,6 +608,18 @@ cifs_destroy_idmaptrees(void)
 	while ((node = rb_first(root)))
 		rb_erase(node, root);
 	spin_unlock(&sidgidlock);
+
+	root = &siduidtree;
+	spin_lock(&uidsidlock);
+	while ((node = rb_first(root)))
+		rb_erase(node, root);
+	spin_unlock(&uidsidlock);
+
+	root = &sidgidtree;
+	spin_lock(&gidsidlock);
+	while ((node = rb_first(root)))
+		rb_erase(node, root);
+	spin_unlock(&gidsidlock);
 }
 
 /* if the two SIDs (roughly equivalent to a UUID for a user or group) are