SUNRPC: Fix a lock recursion in the auth_gss downcall

 When we look up a new cred in the auth_gss downcall so that we can stuff
 the credcache, we do not want that lookup to queue up an upcall in order
 to initialise it. To do an upcall here not only redundant, but since we
 are already holding the inode->i_mutex, it will trigger a lock recursion.

 This patch allows rpcauth cache searches to indicate that they can cope
 with uninitialised credentials.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/auth.h

@@ -50,6 +50,7 @@ struct rpc_cred {
 };
 #define RPCAUTH_CRED_LOCKED	0x0001
 #define RPCAUTH_CRED_UPTODATE	0x0002
+#define RPCAUTH_CRED_NEW	0x0004
 
 #define RPCAUTH_CRED_MAGIC	0x0f4aa4f0
 
@@ -87,6 +88,10 @@ struct rpc_auth {
 						 * uid/gid, fs[ug]id, gids)
 						 */
 
+/* Flags for rpcauth_lookupcred() */
+#define RPCAUTH_LOOKUP_NEW		0x01	/* Accept an uninitialised cred */
+#define RPCAUTH_LOOKUP_ROOTCREDS	0x02	/* This really ought to go! */
+
 /*
  * Client authentication ops
  */

net/sunrpc/auth.c

@@ -184,7 +184,7 @@ rpcauth_gc_credcache(struct rpc_auth *auth, struct hlist_head *free)
  */
 struct rpc_cred *
 rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
-		int taskflags)
+		int flags)
 {
 	struct rpc_cred_cache *cache = auth->au_credcache;
 	HLIST_HEAD(free);
@@ -193,7 +193,7 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
 			*cred = NULL;
 	int		nr = 0;
 
-	if (!(taskflags & RPC_TASK_ROOTCREDS))
+	if (!(flags & RPCAUTH_LOOKUP_ROOTCREDS))
 		nr = acred->uid & RPC_CREDCACHE_MASK;
 retry:
 	spin_lock(&rpc_credcache_lock);
@@ -202,7 +202,7 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
 	hlist_for_each_safe(pos, next, &cache->hashtable[nr]) {
 		struct rpc_cred *entry;
 	       	entry = hlist_entry(pos, struct rpc_cred, cr_hash);
-		if (entry->cr_ops->crmatch(acred, entry, taskflags)) {
+		if (entry->cr_ops->crmatch(acred, entry, flags)) {
 			hlist_del(&entry->cr_hash);
 			cred = entry;
 			break;
@@ -224,7 +224,7 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
 	rpcauth_destroy_credlist(&free);
 
 	if (!cred) {
-		new = auth->au_ops->crcreate(auth, acred, taskflags);
+		new = auth->au_ops->crcreate(auth, acred, flags);
 		if (!IS_ERR(new)) {
 #ifdef RPC_DEBUG
 			new->cr_magic = RPCAUTH_CRED_MAGIC;
@@ -238,7 +238,7 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
 }
 
 struct rpc_cred *
-rpcauth_lookupcred(struct rpc_auth *auth, int taskflags)
+rpcauth_lookupcred(struct rpc_auth *auth, int flags)
 {
 	struct auth_cred acred = {
 		.uid = current->fsuid,
@@ -250,7 +250,7 @@ rpcauth_lookupcred(struct rpc_auth *auth, int taskflags)
 	dprintk("RPC:     looking up %s cred\n",
 		auth->au_ops->au_name);
 	get_group_info(acred.group_info);
-	ret = auth->au_ops->lookup_cred(auth, &acred, taskflags);
+	ret = auth->au_ops->lookup_cred(auth, &acred, flags);
 	put_group_info(acred.group_info);
 	return ret;
 }
@@ -265,11 +265,14 @@ rpcauth_bindcred(struct rpc_task *task)
 		.group_info = current->group_info,
 	};
 	struct rpc_cred *ret;
+	int flags = 0;
 
 	dprintk("RPC: %4d looking up %s cred\n",
 		task->tk_pid, task->tk_auth->au_ops->au_name);
 	get_group_info(acred.group_info);
-	ret = auth->au_ops->lookup_cred(auth, &acred, task->tk_flags);
+	if (task->tk_flags & RPC_TASK_ROOTCREDS)
+		flags |= RPCAUTH_LOOKUP_ROOTCREDS;
+	ret = auth->au_ops->lookup_cred(auth, &acred, flags);
 	if (!IS_ERR(ret))
 		task->tk_msg.rpc_cred = ret;
 	else

net/sunrpc/auth_gss/auth_gss.c

@@ -158,6 +158,7 @@ gss_cred_set_ctx(struct rpc_cred *cred, struct gss_cl_ctx *ctx)
 	old = gss_cred->gc_ctx;
 	gss_cred->gc_ctx = ctx;
 	cred->cr_flags |= RPCAUTH_CRED_UPTODATE;
+	cred->cr_flags &= ~RPCAUTH_CRED_NEW;
 	write_unlock(&gss_ctx_lock);
 	if (old)
 		gss_put_ctx(old);
@@ -580,7 +581,7 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	} else {
 		struct auth_cred acred = { .uid = uid };
 		spin_unlock(&gss_auth->lock);
-		cred = rpcauth_lookup_credcache(clnt->cl_auth, &acred, 0);
+		cred = rpcauth_lookup_credcache(clnt->cl_auth, &acred, RPCAUTH_LOOKUP_NEW);
 		if (IS_ERR(cred)) {
 			err = PTR_ERR(cred);
 			goto err_put_ctx;
@@ -758,13 +759,13 @@ gss_destroy_cred(struct rpc_cred *rc)
  * Lookup RPCSEC_GSS cred for the current process
  */
 static struct rpc_cred *
-gss_lookup_cred(struct rpc_auth *auth, struct auth_cred *acred, int taskflags)
+gss_lookup_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags)
 {
-	return rpcauth_lookup_credcache(auth, acred, taskflags);
+	return rpcauth_lookup_credcache(auth, acred, flags);
 }
 
 static struct rpc_cred *
-gss_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int taskflags)
+gss_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags)
 {
 	struct gss_auth *gss_auth = container_of(auth, struct gss_auth, rpc_auth);
 	struct gss_cred	*cred = NULL;
@@ -785,13 +786,17 @@ gss_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int taskflags)
 	 */
 	cred->gc_flags = 0;
 	cred->gc_base.cr_ops = &gss_credops;
+	cred->gc_base.cr_flags = RPCAUTH_CRED_NEW;
 	cred->gc_service = gss_auth->service;
+	/* Is the caller prepared to initialise the credential? */
+	if (flags & RPCAUTH_LOOKUP_NEW)
+		goto out;
 	do {
 		err = gss_create_upcall(gss_auth, cred);
 	} while (err == -EAGAIN);
 	if (err < 0)
 		goto out_err;
-
+out:
 	return &cred->gc_base;
 
 out_err:
@@ -801,13 +806,21 @@ gss_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int taskflags)
 }
 
 static int
-gss_match(struct auth_cred *acred, struct rpc_cred *rc, int taskflags)
+gss_match(struct auth_cred *acred, struct rpc_cred *rc, int flags)
 {
 	struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base);
 
+	/*
+	 * If the searchflags have set RPCAUTH_LOOKUP_NEW, then
+	 * we don't really care if the credential has expired or not,
+	 * since the caller should be prepared to reinitialise it.
+	 */
+	if ((flags & RPCAUTH_LOOKUP_NEW) && (rc->cr_flags & RPCAUTH_CRED_NEW))
+		goto out;
 	/* Don't match with creds that have expired. */
 	if (gss_cred->gc_ctx && time_after(jiffies, gss_cred->gc_ctx->gc_expiry))
 		return 0;
+out:
 	return (rc->cr_uid == acred->uid);
 }
 

net/sunrpc/auth_unix.c

@@ -75,7 +75,7 @@ unx_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags)
 
 	atomic_set(&cred->uc_count, 1);
 	cred->uc_flags = RPCAUTH_CRED_UPTODATE;
-	if (flags & RPC_TASK_ROOTCREDS) {
+	if (flags & RPCAUTH_LOOKUP_ROOTCREDS) {
 		cred->uc_uid = 0;
 		cred->uc_gid = 0;
 		cred->uc_gids[0] = NOGROUP;
@@ -108,12 +108,12 @@ unx_destroy_cred(struct rpc_cred *cred)
  * request root creds (e.g. for NFS swapping).
  */
 static int
-unx_match(struct auth_cred *acred, struct rpc_cred *rcred, int taskflags)
+unx_match(struct auth_cred *acred, struct rpc_cred *rcred, int flags)
 {
 	struct unx_cred	*cred = (struct unx_cred *) rcred;
 	int		i;
 
-	if (!(taskflags & RPC_TASK_ROOTCREDS)) {
+	if (!(flags & RPCAUTH_LOOKUP_ROOTCREDS)) {
 		int groups;
 
 		if (cred->uc_uid != acred->uid