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Switch to recallocarray() for a few operations.  Both growth and shrinkage
are handled safely, and there also is no need for preallocation dances.
Future changes in this area will be less error prone.
Review and one bug found by markus

/* $OpenBSD: ssh-pkcs11.c,v 1.25 2017/05/31 09:15:42 deraadt Exp $ */
/*
 * Copyright (c) 2010 Markus Friedl.  All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/queue.h>
#include <stdarg.h>
#include <stdio.h>

#include <string.h>
#include <dlfcn.h>

#include <openssl/x509.h>

#define CRYPTOKI_COMPAT
#include "pkcs11.h"

#include "log.h"
#include "misc.h"
#include "sshkey.h"
#include "ssh-pkcs11.h"
#include "xmalloc.h"

struct pkcs11_slotinfo {
	CK_TOKEN_INFO		token;
	CK_SESSION_HANDLE	session;
	int			logged_in;
};

struct pkcs11_provider {
	char			*name;
	void			*handle;
	CK_FUNCTION_LIST	*function_list;
	CK_INFO			info;
	CK_ULONG		nslots;
	CK_SLOT_ID		*slotlist;
	struct pkcs11_slotinfo	*slotinfo;
	int			valid;
	int			refcount;
	TAILQ_ENTRY(pkcs11_provider) next;
};

TAILQ_HEAD(, pkcs11_provider) pkcs11_providers;

struct pkcs11_key {
	struct pkcs11_provider	*provider;
	CK_ULONG		slotidx;
	int			(*orig_finish)(RSA *rsa);
	RSA_METHOD		rsa_method;
	char			*keyid;
	int			keyid_len;
};

int pkcs11_interactive = 0;

int
pkcs11_init(int interactive)
{
	pkcs11_interactive = interactive;
	TAILQ_INIT(&pkcs11_providers);
	return (0);
}

/*
 * finalize a provider shared libarary, it's no longer usable.
 * however, there might still be keys referencing this provider,
 * so the actuall freeing of memory is handled by pkcs11_provider_unref().
 * this is called when a provider gets unregistered.
 */
static void
pkcs11_provider_finalize(struct pkcs11_provider *p)
{
	CK_RV rv;
	CK_ULONG i;

	debug("pkcs11_provider_finalize: %p refcount %d valid %d",
	    p, p->refcount, p->valid);
	if (!p->valid)
		return;
	for (i = 0; i < p->nslots; i++) {
		if (p->slotinfo[i].session &&
		    (rv = p->function_list->C_CloseSession(
		    p->slotinfo[i].session)) != CKR_OK)
			error("C_CloseSession failed: %lu", rv);
	}
	if ((rv = p->function_list->C_Finalize(NULL)) != CKR_OK)
		error("C_Finalize failed: %lu", rv);
	p->valid = 0;
	p->function_list = NULL;
#ifdef HAVE_DLOPEN
	dlclose(p->handle);
#endif
}

/*
 * remove a reference to the provider.
 * called when a key gets destroyed or when the provider is unregistered.
 */
static void
pkcs11_provider_unref(struct pkcs11_provider *p)
{
	debug("pkcs11_provider_unref: %p refcount %d", p, p->refcount);
	if (--p->refcount <= 0) {
		if (p->valid)
			error("pkcs11_provider_unref: %p still valid", p);
		free(p->slotlist);
		free(p->slotinfo);
		free(p);
	}
}

/* unregister all providers, keys might still point to the providers */
void
pkcs11_terminate(void)
{
	struct pkcs11_provider *p;

	while ((p = TAILQ_FIRST(&pkcs11_providers)) != NULL) {
		TAILQ_REMOVE(&pkcs11_providers, p, next);
		pkcs11_provider_finalize(p);
		pkcs11_provider_unref(p);
	}
}

/* lookup provider by name */
static struct pkcs11_provider *
pkcs11_provider_lookup(char *provider_id)
{
	struct pkcs11_provider *p;

	TAILQ_FOREACH(p, &pkcs11_providers, next) {
		debug("check %p %s", p, p->name);
		if (!strcmp(provider_id, p->name))
			return (p);
	}
	return (NULL);
}

/* unregister provider by name */
int
pkcs11_del_provider(char *provider_id)
{
	struct pkcs11_provider *p;

	if ((p = pkcs11_provider_lookup(provider_id)) != NULL) {
		TAILQ_REMOVE(&pkcs11_providers, p, next);
		pkcs11_provider_finalize(p);
		pkcs11_provider_unref(p);
		return (0);
	}
	return (-1);
}

/* openssl callback for freeing an RSA key */
static int
pkcs11_rsa_finish(RSA *rsa)
{
	struct pkcs11_key	*k11;
	int rv = -1;

	if ((k11 = RSA_get_app_data(rsa)) != NULL) {
		if (k11->orig_finish)
			rv = k11->orig_finish(rsa);
		if (k11->provider)
			pkcs11_provider_unref(k11->provider);
		free(k11->keyid);
		free(k11);
	}
	return (rv);
}

/* find a single 'obj' for given attributes */
static int
pkcs11_find(struct pkcs11_provider *p, CK_ULONG slotidx, CK_ATTRIBUTE *attr,
    CK_ULONG nattr, CK_OBJECT_HANDLE *obj)
{
	CK_FUNCTION_LIST	*f;
	CK_SESSION_HANDLE	session;
	CK_ULONG		nfound = 0;
	CK_RV			rv;
	int			ret = -1;

	f = p->function_list;
	session = p->slotinfo[slotidx].session;
	if ((rv = f->C_FindObjectsInit(session, attr, nattr)) != CKR_OK) {
		error("C_FindObjectsInit failed (nattr %lu): %lu", nattr, rv);
		return (-1);
	}
	if ((rv = f->C_FindObjects(session, obj, 1, &nfound)) != CKR_OK ||
	    nfound != 1) {
		debug("C_FindObjects failed (nfound %lu nattr %lu): %lu",
		    nfound, nattr, rv);
	} else
		ret = 0;
	if ((rv = f->C_FindObjectsFinal(session)) != CKR_OK)
		error("C_FindObjectsFinal failed: %lu", rv);
	return (ret);
}

/* openssl callback doing the actual signing operation */
static int
pkcs11_rsa_private_encrypt(int flen, const u_char *from, u_char *to, RSA *rsa,
    int padding)
{
	struct pkcs11_key	*k11;
	struct pkcs11_slotinfo	*si;
	CK_FUNCTION_LIST	*f;
	CK_OBJECT_HANDLE	obj;
	CK_ULONG		tlen = 0;
	CK_RV			rv;
	CK_OBJECT_CLASS		private_key_class = CKO_PRIVATE_KEY;
	CK_BBOOL		true_val = CK_TRUE;
	CK_MECHANISM		mech = {
		CKM_RSA_PKCS, NULL_PTR, 0
	};
	CK_ATTRIBUTE		key_filter[] = {
		{CKA_CLASS, &private_key_class, sizeof(private_key_class) },
		{CKA_ID, NULL, 0},
		{CKA_SIGN, &true_val, sizeof(true_val) }
	};
	char			*pin = NULL, prompt[1024];
	int			rval = -1;

	if ((k11 = RSA_get_app_data(rsa)) == NULL) {
		error("RSA_get_app_data failed for rsa %p", rsa);
		return (-1);
	}
	if (!k11->provider || !k11->provider->valid) {
		error("no pkcs11 (valid) provider for rsa %p", rsa);
		return (-1);
	}
	f = k11->provider->function_list;
	si = &k11->provider->slotinfo[k11->slotidx];
	if ((si->token.flags & CKF_LOGIN_REQUIRED) && !si->logged_in) {
		if (!pkcs11_interactive) {
			error("need pin entry%s", (si->token.flags &
			    CKF_PROTECTED_AUTHENTICATION_PATH) ?
			    " on reader keypad" : "");
			return (-1);
		}
		if (si->token.flags & CKF_PROTECTED_AUTHENTICATION_PATH)
			verbose("Deferring PIN entry to reader keypad.");
		else {
			snprintf(prompt, sizeof(prompt),
			    "Enter PIN for '%s': ", si->token.label);
			pin = read_passphrase(prompt, RP_ALLOW_EOF);
			if (pin == NULL)
				return (-1);	/* bail out */
		}
		rv = f->C_Login(si->session, CKU_USER, (u_char *)pin,
		    (pin != NULL) ? strlen(pin) : 0);
		if (pin != NULL) {
			explicit_bzero(pin, strlen(pin));
			free(pin);
		}
		if (rv != CKR_OK && rv != CKR_USER_ALREADY_LOGGED_IN) {
			error("C_Login failed: %lu", rv);
			return (-1);
		}
		si->logged_in = 1;
	}
	key_filter[1].pValue = k11->keyid;
	key_filter[1].ulValueLen = k11->keyid_len;
	/* try to find object w/CKA_SIGN first, retry w/o */
	if (pkcs11_find(k11->provider, k11->slotidx, key_filter, 3, &obj) < 0 &&
	    pkcs11_find(k11->provider, k11->slotidx, key_filter, 2, &obj) < 0) {
		error("cannot find private key");
	} else if ((rv = f->C_SignInit(si->session, &mech, obj)) != CKR_OK) {
		error("C_SignInit failed: %lu", rv);
	} else {
		/* XXX handle CKR_BUFFER_TOO_SMALL */
		tlen = RSA_size(rsa);
		rv = f->C_Sign(si->session, (CK_BYTE *)from, flen, to, &tlen);
		if (rv == CKR_OK) 
			rval = tlen;
		else 
			error("C_Sign failed: %lu", rv);
	}
	return (rval);
}

static int
pkcs11_rsa_private_decrypt(int flen, const u_char *from, u_char *to, RSA *rsa,
    int padding)
{
	return (-1);
}

/* redirect private key operations for rsa key to pkcs11 token */
static int
pkcs11_rsa_wrap(struct pkcs11_provider *provider, CK_ULONG slotidx,
    CK_ATTRIBUTE *keyid_attrib, RSA *rsa)
{
	struct pkcs11_key	*k11;
	const RSA_METHOD	*def = RSA_get_default_method();

	k11 = xcalloc(1, sizeof(*k11));
	k11->provider = provider;
	provider->refcount++;	/* provider referenced by RSA key */
	k11->slotidx = slotidx;
	/* identify key object on smartcard */
	k11->keyid_len = keyid_attrib->ulValueLen;
	if (k11->keyid_len > 0) {
		k11->keyid = xmalloc(k11->keyid_len);
		memcpy(k11->keyid, keyid_attrib->pValue, k11->keyid_len);
	}
	k11->orig_finish = def->finish;
	memcpy(&k11->rsa_method, def, sizeof(k11->rsa_method));
	k11->rsa_method.name = "pkcs11";
	k11->rsa_method.rsa_priv_enc = pkcs11_rsa_private_encrypt;
	k11->rsa_method.rsa_priv_dec = pkcs11_rsa_private_decrypt;
	k11->rsa_method.finish = pkcs11_rsa_finish;
	RSA_set_method(rsa, &k11->rsa_method);
	RSA_set_app_data(rsa, k11);
	return (0);
}

/* remove trailing spaces */
static void
rmspace(u_char *buf, size_t len)
{
	size_t i;

	if (!len)
		return;
	for (i = len - 1;  i > 0; i--)
		if (i == len - 1 || buf[i] == ' ')
			buf[i] = '\0';
		else
			break;
}

/*
 * open a pkcs11 session and login if required.
 * if pin == NULL we delay login until key use
 */
static int
pkcs11_open_session(struct pkcs11_provider *p, CK_ULONG slotidx, char *pin)
{
	CK_RV			rv;
	CK_FUNCTION_LIST	*f;
	CK_SESSION_HANDLE	session;
	int			login_required;

	f = p->function_list;
	login_required = p->slotinfo[slotidx].token.flags & CKF_LOGIN_REQUIRED;
	if (pin && login_required && !strlen(pin)) {
		error("pin required");
		return (-1);
	}
	if ((rv = f->C_OpenSession(p->slotlist[slotidx], CKF_RW_SESSION|
	    CKF_SERIAL_SESSION, NULL, NULL, &session))
	    != CKR_OK) {
		error("C_OpenSession failed: %lu", rv);
		return (-1);
	}
	if (login_required && pin) {
		rv = f->C_Login(session, CKU_USER,
		    (u_char *)pin, strlen(pin));
		if (rv != CKR_OK && rv != CKR_USER_ALREADY_LOGGED_IN) {
			error("C_Login failed: %lu", rv);
			if ((rv = f->C_CloseSession(session)) != CKR_OK)
				error("C_CloseSession failed: %lu", rv);
			return (-1);
		}
		p->slotinfo[slotidx].logged_in = 1;
	}
	p->slotinfo[slotidx].session = session;
	return (0);
}

/*
 * lookup public keys for token in slot identified by slotidx,
 * add 'wrapped' public keys to the 'keysp' array and increment nkeys.
 * keysp points to an (possibly empty) array with *nkeys keys.
 */
static int pkcs11_fetch_keys_filter(struct pkcs11_provider *, CK_ULONG,
    CK_ATTRIBUTE [], CK_ATTRIBUTE [3], struct sshkey ***, int *)
	__attribute__((__bounded__(__minbytes__,4, 3 * sizeof(CK_ATTRIBUTE))));

static int
pkcs11_fetch_keys(struct pkcs11_provider *p, CK_ULONG slotidx,
    struct sshkey ***keysp, int *nkeys)
{
	CK_OBJECT_CLASS		pubkey_class = CKO_PUBLIC_KEY;
	CK_OBJECT_CLASS		cert_class = CKO_CERTIFICATE;
	CK_ATTRIBUTE		pubkey_filter[] = {
		{ CKA_CLASS, &pubkey_class, sizeof(pubkey_class) }
	};
	CK_ATTRIBUTE		cert_filter[] = {
		{ CKA_CLASS, &cert_class, sizeof(cert_class) }
	};
	CK_ATTRIBUTE		pubkey_attribs[] = {
		{ CKA_ID, NULL, 0 },
		{ CKA_MODULUS, NULL, 0 },
		{ CKA_PUBLIC_EXPONENT, NULL, 0 }
	};
	CK_ATTRIBUTE		cert_attribs[] = {
		{ CKA_ID, NULL, 0 },
		{ CKA_SUBJECT, NULL, 0 },
		{ CKA_VALUE, NULL, 0 }
	};

	if (pkcs11_fetch_keys_filter(p, slotidx, pubkey_filter, pubkey_attribs,
	    keysp, nkeys) < 0 ||
	    pkcs11_fetch_keys_filter(p, slotidx, cert_filter, cert_attribs,
	    keysp, nkeys) < 0)
		return (-1);
	return (0);
}

static int
pkcs11_key_included(struct sshkey ***keysp, int *nkeys, struct sshkey *key)
{
	int i;

	for (i = 0; i < *nkeys; i++)
		if (sshkey_equal(key, (*keysp)[i]))
			return (1);
	return (0);
}

static int
pkcs11_fetch_keys_filter(struct pkcs11_provider *p, CK_ULONG slotidx,
    CK_ATTRIBUTE filter[], CK_ATTRIBUTE attribs[3],
    struct sshkey ***keysp, int *nkeys)
{
	struct sshkey		*key;
	RSA			*rsa;
	X509 			*x509;
	EVP_PKEY		*evp;
	int			i;
	const u_char		*cp;
	CK_RV			rv;
	CK_OBJECT_HANDLE	obj;
	CK_ULONG		nfound;
	CK_SESSION_HANDLE	session;
	CK_FUNCTION_LIST	*f;

	f = p->function_list;
	session = p->slotinfo[slotidx].session;
	/* setup a filter the looks for public keys */
	if ((rv = f->C_FindObjectsInit(session, filter, 1)) != CKR_OK) {
		error("C_FindObjectsInit failed: %lu", rv);
		return (-1);
	}
	while (1) {
		/* XXX 3 attributes in attribs[] */
		for (i = 0; i < 3; i++) {
			attribs[i].pValue = NULL;
			attribs[i].ulValueLen = 0;
		}
		if ((rv = f->C_FindObjects(session, &obj, 1, &nfound)) != CKR_OK
		    || nfound == 0)
			break;
		/* found a key, so figure out size of the attributes */
		if ((rv = f->C_GetAttributeValue(session, obj, attribs, 3))
		    != CKR_OK) {
			error("C_GetAttributeValue failed: %lu", rv);
			continue;
		}
		/*
		 * Allow CKA_ID (always first attribute) to be empty, but
		 * ensure that none of the others are zero length.
		 * XXX assumes CKA_ID is always first.
		 */
		if (attribs[1].ulValueLen == 0 ||
		    attribs[2].ulValueLen == 0) {
			continue;
		}
		/* allocate buffers for attributes */
		for (i = 0; i < 3; i++) {
			if (attribs[i].ulValueLen > 0) {
				attribs[i].pValue = xmalloc(
				    attribs[i].ulValueLen);
			}
		}

		/*
		 * retrieve ID, modulus and public exponent of RSA key,
		 * or ID, subject and value for certificates.
		 */
		rsa = NULL;
		if ((rv = f->C_GetAttributeValue(session, obj, attribs, 3))
		    != CKR_OK) {
			error("C_GetAttributeValue failed: %lu", rv);
		} else if (attribs[1].type == CKA_MODULUS ) {
			if ((rsa = RSA_new()) == NULL) {
				error("RSA_new failed");
			} else {
				rsa->n = BN_bin2bn(attribs[1].pValue,
				    attribs[1].ulValueLen, NULL);
				rsa->e = BN_bin2bn(attribs[2].pValue,
				    attribs[2].ulValueLen, NULL);
			}
		} else {
			cp = attribs[2].pValue;
			if ((x509 = X509_new()) == NULL) {
				error("X509_new failed");
			} else if (d2i_X509(&x509, &cp, attribs[2].ulValueLen)
			    == NULL) {
				error("d2i_X509 failed");
			} else if ((evp = X509_get_pubkey(x509)) == NULL ||
			    evp->type != EVP_PKEY_RSA ||
			    evp->pkey.rsa == NULL) {
				debug("X509_get_pubkey failed or no rsa");
			} else if ((rsa = RSAPublicKey_dup(evp->pkey.rsa))
			    == NULL) {
				error("RSAPublicKey_dup");
			}
			if (x509)
				X509_free(x509);
		}
		if (rsa && rsa->n && rsa->e &&
		    pkcs11_rsa_wrap(p, slotidx, &attribs[0], rsa) == 0) {
			if ((key = sshkey_new(KEY_UNSPEC)) == NULL)
				fatal("sshkey_new failed");
			key->rsa = rsa;
			key->type = KEY_RSA;
			key->flags |= SSHKEY_FLAG_EXT;
			if (pkcs11_key_included(keysp, nkeys, key)) {
				sshkey_free(key);
			} else {
				/* expand key array and add key */
				*keysp = xrecallocarray(*keysp, *nkeys,
				    *nkeys + 1, sizeof(struct sshkey *));
				(*keysp)[*nkeys] = key;
				*nkeys = *nkeys + 1;
				debug("have %d keys", *nkeys);
			}
		} else if (rsa) {
			RSA_free(rsa);
		}
		for (i = 0; i < 3; i++)
			free(attribs[i].pValue);
	}
	if ((rv = f->C_FindObjectsFinal(session)) != CKR_OK)
		error("C_FindObjectsFinal failed: %lu", rv);
	return (0);
}

#ifdef HAVE_DLOPEN
/* register a new provider, fails if provider already exists */
int
pkcs11_add_provider(char *provider_id, char *pin, struct sshkey ***keyp)
{
	int nkeys, need_finalize = 0;
	struct pkcs11_provider *p = NULL;
	void *handle = NULL;
	CK_RV (*getfunctionlist)(CK_FUNCTION_LIST **);
	CK_RV rv;
	CK_FUNCTION_LIST *f = NULL;
	CK_TOKEN_INFO *token;
	CK_ULONG i;

	*keyp = NULL;
	if (pkcs11_provider_lookup(provider_id) != NULL) {
		debug("%s: provider already registered: %s",
		    __func__, provider_id);
		goto fail;
	}
	/* open shared pkcs11-libarary */
	if ((handle = dlopen(provider_id, RTLD_NOW)) == NULL) {
		error("dlopen %s failed: %s", provider_id, dlerror());
		goto fail;
	}
	if ((getfunctionlist = dlsym(handle, "C_GetFunctionList")) == NULL) {
		error("dlsym(C_GetFunctionList) failed: %s", dlerror());
		goto fail;
	}
	p = xcalloc(1, sizeof(*p));
	p->name = xstrdup(provider_id);
	p->handle = handle;
	/* setup the pkcs11 callbacks */
	if ((rv = (*getfunctionlist)(&f)) != CKR_OK) {
		error("C_GetFunctionList for provider %s failed: %lu",
		    provider_id, rv);
		goto fail;
	}
	p->function_list = f;
	if ((rv = f->C_Initialize(NULL)) != CKR_OK) {
		error("C_Initialize for provider %s failed: %lu",
		    provider_id, rv);
		goto fail;
	}
	need_finalize = 1;
	if ((rv = f->C_GetInfo(&p->info)) != CKR_OK) {
		error("C_GetInfo for provider %s failed: %lu",
		    provider_id, rv);
		goto fail;
	}
	rmspace(p->info.manufacturerID, sizeof(p->info.manufacturerID));
	rmspace(p->info.libraryDescription, sizeof(p->info.libraryDescription));
	debug("provider %s: manufacturerID <%s> cryptokiVersion %d.%d"
	    " libraryDescription <%s> libraryVersion %d.%d",
	    provider_id,
	    p->info.manufacturerID,
	    p->info.cryptokiVersion.major,
	    p->info.cryptokiVersion.minor,
	    p->info.libraryDescription,
	    p->info.libraryVersion.major,
	    p->info.libraryVersion.minor);
	if ((rv = f->C_GetSlotList(CK_TRUE, NULL, &p->nslots)) != CKR_OK) {
		error("C_GetSlotList failed: %lu", rv);
		goto fail;
	}
	if (p->nslots == 0) {
		debug("%s: provider %s returned no slots", __func__,
		    provider_id);
		goto fail;
	}
	p->slotlist = xcalloc(p->nslots, sizeof(CK_SLOT_ID));
	if ((rv = f->C_GetSlotList(CK_TRUE, p->slotlist, &p->nslots))
	    != CKR_OK) {
		error("C_GetSlotList for provider %s failed: %lu",
		    provider_id, rv);
		goto fail;
	}
	p->slotinfo = xcalloc(p->nslots, sizeof(struct pkcs11_slotinfo));
	p->valid = 1;
	nkeys = 0;
	for (i = 0; i < p->nslots; i++) {
		token = &p->slotinfo[i].token;
		if ((rv = f->C_GetTokenInfo(p->slotlist[i], token))
		    != CKR_OK) {
			error("C_GetTokenInfo for provider %s slot %lu "
			    "failed: %lu", provider_id, (unsigned long)i, rv);
			continue;
		}
		if ((token->flags & CKF_TOKEN_INITIALIZED) == 0) {
			debug2("%s: ignoring uninitialised token in "
			    "provider %s slot %lu", __func__,
			    provider_id, (unsigned long)i);
			continue;
		}
		rmspace(token->label, sizeof(token->label));
		rmspace(token->manufacturerID, sizeof(token->manufacturerID));
		rmspace(token->model, sizeof(token->model));
		rmspace(token->serialNumber, sizeof(token->serialNumber));
		debug("provider %s slot %lu: label <%s> manufacturerID <%s> "
		    "model <%s> serial <%s> flags 0x%lx",
		    provider_id, (unsigned long)i,
		    token->label, token->manufacturerID, token->model,
		    token->serialNumber, token->flags);
		/* open session, login with pin and retrieve public keys */
		if (pkcs11_open_session(p, i, pin) == 0)
			pkcs11_fetch_keys(p, i, keyp, &nkeys);
	}
	if (nkeys > 0) {
		TAILQ_INSERT_TAIL(&pkcs11_providers, p, next);
		p->refcount++;	/* add to provider list */
		return (nkeys);
	}
	debug("%s: provider %s returned no keys", __func__, provider_id);
	/* don't add the provider, since it does not have any keys */
fail:
	if (need_finalize && (rv = f->C_Finalize(NULL)) != CKR_OK)
		error("C_Finalize for provider %s failed: %lu",
		    provider_id, rv);
	if (p) {
		free(p->slotlist);
		free(p->slotinfo);
		free(p);
	}
	if (handle)
		dlclose(handle);
	return (-1);
}
#else
int
pkcs11_add_provider(char *provider_id, char *pin, struct sshkey ***keyp)
{
	error("dlopen() not supported");
	return (-1);
}
#endif