These patches are a work in progress. They add the option to store GSS
credentials in user keyrings as an alternative to the credential cache
hashtables that are currently used. The goal is to give users the
ability to destroy their credentials on-demand.
There have been other attempts to give users the ability to destroy
their GSS credentials in the past, for example:
https://lore.kernel.org/all/[email protected]/T/
and
https://lore.kernel.org/linux-nfs/[email protected]/
But those attempts were not accepted, so I wanted to get some feedback
on what I currently have before trying to tackle some of the more thorny
issues, such as what to do when a user has files open for write,
potentially with dirty data to be written out.
These patches are also available at:
https://github.com/scottmayhew/linux/tree/gss-cred-keyring
Here's a quick demo:
[smayhew@centos9 ~]$ sudo mount nfs:/export /mnt/t
[smayhew@centos9 ~]$ ls -l /mnt/t/test[12]
-rw-r--r--. 1 testuser1 testuser1 32 Apr 20 15:34 /mnt/t/test1
-rw-r--r--. 1 testuser2 testuser2 32 Apr 20 15:33 /mnt/t/test2
[smayhew@centos9 ~]$ kinit testuser1
Password for [email protected]:
[smayhew@centos9 ~]$ date >/mnt/t/test1
[smayhew@centos9 ~]$ keyctl show
Session Keyring
400651412 --alswrv 1000 1000 keyring: _ses
376802674 --alswrv 1000 65534 \_ keyring: _uid.1000
297894262 --als--v 1000 1000 \_ gss_cred: clid:1 id:1000 princ:(none)
[smayhew@centos9 ~]$ date >/mnt/t/test2
-bash: /mnt/t/test2: Permission denied
[smayhew@centos9 ~]$ kinit testuser2
Password for [email protected]:
[smayhew@centos9 ~]$ keyctl unlink 297894262
1 links removed
Note: At this point the old gss_cred hasn't actually been destroyed,
because the key that is referencing it is also linked to a special
keyring hanging off the gss_auth structure. When the user creates a new
gss_cred and the key referencing the new gss_cred is linked to the
gss_auth keyring, that causes the old gss_cred to be destroyed and a
RPCSEC_GSS_DESTROY is sent to the server. If the user were to unlink
their gss_cred key and do nothing else, then the cred would be destroyed
when the gss_auth is destroyed (i.e. on umount).
[smayhew@centos9 ~]$ keyctl show
Session Keyring
400651412 --alswrv 1000 1000 keyring: _ses
376802674 --alswrv 1000 65534 \_ keyring: _uid.1000
[smayhew@centos9 ~]$ date >/mnt/t/test2
[smayhew@centos9 ~]$ keyctl show
Session Keyring
400651412 --alswrv 1000 1000 keyring: _ses
376802674 --alswrv 1000 65534 \_ keyring: _uid.1000
83204766 --als--v 1000 1000 \_ gss_cred: clid:1 id:1000 princ:(none)
[smayhew@centos9 ~]$ date >/mnt/t/test1
-bash: /mnt/t/test1: Permission denied
-Scott
Scott Mayhew (5):
keys: export keyring_ptr_to_key()
keys: add keyring_gc_custom()
keys: add dest_keyring parameter to request_key_with_auxdata()
keys: add the ability to search user keyrings in
search_cred_keyrings_rcu()
SUNRPC: store GSS creds in keyrings
fs/nfs/nfs4idmap.c | 2 +-
include/linux/key.h | 9 +-
include/linux/sunrpc/auth.h | 4 +-
include/trace/events/rpcgss.h | 46 ++++-
net/sunrpc/auth.c | 9 +-
net/sunrpc/auth_gss/auth_gss.c | 338 +++++++++++++++++++++++++++++++--
security/keys/internal.h | 1 +
security/keys/keyring.c | 16 +-
security/keys/process_keys.c | 78 ++++++--
security/keys/request_key.c | 5 +-
10 files changed, 470 insertions(+), 38 deletions(-)
--
2.39.2
We want to be able to garbage collect keyrings using a custom select
iterator, which will need to use keyring_ptr_to_key().
Signed-off-by: Scott Mayhew <[email protected]>
---
include/linux/key.h | 2 ++
security/keys/keyring.c | 5 ++++-
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/linux/key.h b/include/linux/key.h
index 8dc7f7c3088b..3f4c6d6df921 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -417,6 +417,8 @@ extern int key_move(struct key *key,
extern int key_unlink(struct key *keyring,
struct key *key);
+extern inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x);
+
extern struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
const struct cred *cred,
key_perm_t perm,
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 4448758f643a..c57f3cef32fa 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -37,11 +37,14 @@ static inline bool keyring_ptr_is_keyring(const struct assoc_array_ptr *x)
{
return (unsigned long)x & KEYRING_PTR_SUBTYPE;
}
-static inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x)
+
+inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x)
{
void *object = assoc_array_ptr_to_leaf(x);
return (struct key *)((unsigned long)object & ~KEYRING_PTR_SUBTYPE);
}
+EXPORT_SYMBOL_GPL(keyring_ptr_to_key);
+
static inline void *keyring_key_to_ptr(struct key *key)
{
if (key->type == &key_type_keyring)
--
2.39.2
We want to store GSS creds in user keyrings. Add a dest_keyring
parameter to request_key_with_auxdata() so we can do that.
Signed-off-by: Scott Mayhew <[email protected]>
---
fs/nfs/nfs4idmap.c | 2 +-
include/linux/key.h | 3 ++-
security/keys/request_key.c | 5 +++--
3 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/nfs/nfs4idmap.c b/fs/nfs/nfs4idmap.c
index 25a7c771cfd8..15d4fc30bf50 100644
--- a/fs/nfs/nfs4idmap.c
+++ b/fs/nfs/nfs4idmap.c
@@ -292,7 +292,7 @@ static struct key *nfs_idmap_request_key(const char *name, size_t namelen,
if (IS_ERR(rkey)) {
mutex_lock(&idmap->idmap_mutex);
rkey = request_key_with_auxdata(&key_type_id_resolver_legacy,
- desc, NULL, "", 0, idmap);
+ desc, NULL, "", 0, idmap, NULL);
mutex_unlock(&idmap->idmap_mutex);
}
if (!IS_ERR(rkey))
diff --git a/include/linux/key.h b/include/linux/key.h
index 6cfc60aca505..009dfd3d27b0 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -333,7 +333,8 @@ extern struct key *request_key_with_auxdata(struct key_type *type,
struct key_tag *domain_tag,
const void *callout_info,
size_t callout_len,
- void *aux);
+ void *aux,
+ struct key *dest_keyring);
/**
* request_key - Request a key and wait for construction
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 07a0ef2baacd..1424a6fa4c9d 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -735,14 +735,15 @@ struct key *request_key_with_auxdata(struct key_type *type,
struct key_tag *domain_tag,
const void *callout_info,
size_t callout_len,
- void *aux)
+ void *aux,
+ struct key *dest_keyring)
{
struct key *key;
int ret;
key = request_key_and_link(type, description, domain_tag,
callout_info, callout_len,
- aux, NULL, KEY_ALLOC_IN_QUOTA);
+ aux, dest_keyring, KEY_ALLOC_IN_QUOTA);
if (!IS_ERR(key)) {
ret = wait_for_key_construction(key, false);
if (ret < 0) {
--
2.39.2
This patch adds the option to store GSS credentials in keyrings as an
alternative to the RPC credential cache, to give users the ability to
destroy their GSS credentials on demand via 'keyctl unlink'.
Summary of the changes:
- Added key_type key_type_gss_cred and associated functions. The
request_key function makes use of the existing upcall mechanism to
gssd.
- Added a keyring to the gss_auth struct to allow all of the assocated
GSS credentials to be destroyed on RPC client shutdown (when the
filesystem is unmounted).
- The key description contains the RPC client id, the user id, and the
principal (for machine creds).
- The key payload contains the address of the gss_cred.
- The key is linked to the user's user keyring (KEY_SPEC_USER_KEYRING)
as well as to the keyring on the gss_auth struct.
- gss_cred_init() now takes an optional pointer to an authkey, which is
passed down to gss_create_upcall() and gss_setup_upcall(), where it is
added to the gss_msg. This is used for complete_request_key() after
the upcall is done.
- put_rpccred() now returns a bool to indicate whether it called
crdestroy(), and is used by gss_key_revoke() and gss_key_destroy() to
determine whether to clear the key payload.
- gss_fill_context() now returns the GSS context's timeout via the tout
parameter, which is used to set the timeout of the key.
- Added the module parameter 'use_keyring'. When set to true, the GSS
credentials are stored in the keyrings. When false, the GSS
credentials are stored in the RPC credential caches.
- Added a tracepoint to log the result of the key request, which prints
either the key serial or an error return value.
Signed-off-by: Scott Mayhew <[email protected]>
---
include/linux/sunrpc/auth.h | 4 +-
include/trace/events/rpcgss.h | 46 ++++-
net/sunrpc/auth.c | 9 +-
net/sunrpc/auth_gss/auth_gss.c | 338 +++++++++++++++++++++++++++++++--
4 files changed, 376 insertions(+), 21 deletions(-)
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 3e6ce288a7fc..2a1fd8409396 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -124,7 +124,7 @@ struct rpc_authops {
struct rpc_credops {
const char * cr_name; /* Name of the auth flavour */
- int (*cr_init)(struct rpc_auth *, struct rpc_cred *);
+ int (*cr_init)(struct rpc_auth *, struct rpc_cred *, struct key *);
void (*crdestroy)(struct rpc_cred *);
int (*crmatch)(struct auth_cred *, struct rpc_cred *, int);
@@ -162,7 +162,7 @@ int rpcauth_get_gssinfo(rpc_authflavor_t,
struct rpc_cred * rpcauth_lookup_credcache(struct rpc_auth *, struct auth_cred *, int, gfp_t);
void rpcauth_init_cred(struct rpc_cred *, const struct auth_cred *, struct rpc_auth *, const struct rpc_credops *);
struct rpc_cred * rpcauth_lookupcred(struct rpc_auth *, int);
-void put_rpccred(struct rpc_cred *);
+bool put_rpccred(struct rpc_cred *);
int rpcauth_marshcred(struct rpc_task *task,
struct xdr_stream *xdr);
int rpcauth_checkverf(struct rpc_task *task,
diff --git a/include/trace/events/rpcgss.h b/include/trace/events/rpcgss.h
index ba2d96a1bc2f..3a9a0b343c4a 100644
--- a/include/trace/events/rpcgss.h
+++ b/include/trace/events/rpcgss.h
@@ -626,6 +626,40 @@ TRACE_EVENT(rpcgss_context,
__entry->timeout, __entry->len, __get_str(acceptor))
);
+TRACE_EVENT(rpcgss_request_key_result,
+ TP_PROTO(
+ const struct auth_cred *acred,
+ const struct key *key
+ ),
+
+ TP_ARGS(acred, key),
+
+ TP_STRUCT__entry(
+ __field(u32, uid)
+ __string(principal, acred->principal)
+ __field(const void *, credkey)
+ __field(int, serial)
+ __field(int, error)
+ ),
+
+ TP_fast_assign(
+ __entry->uid = from_kuid(&init_user_ns, acred->cred->fsuid);
+ __assign_str(principal, acred->principal);
+ if (IS_ERR(key)) {
+ __entry->credkey = 0;
+ __entry->serial = 0;
+ __entry->error = PTR_ERR(key);
+ } else {
+ __entry->credkey = key;
+ __entry->serial = key->serial;
+ __entry->error = 0;
+ }
+ ),
+
+ TP_printk(" for acred { uid %u princ %s }, key=%px serial=%d error=%d",
+ __entry->uid, __get_str(principal), __entry->credkey,
+ __entry->serial, __entry->error)
+);
/**
** Miscellaneous events
@@ -645,24 +679,28 @@ TRACE_DEFINE_ENUM(RPC_AUTH_GSS_KRB5P);
TRACE_EVENT(rpcgss_createauth,
TP_PROTO(
unsigned int flavor,
- int error
+ int error,
+ const struct key *key
),
- TP_ARGS(flavor, error),
+ TP_ARGS(flavor, error, key),
TP_STRUCT__entry(
__field(unsigned int, flavor)
__field(int, error)
+ __field(const void *, keyring)
),
TP_fast_assign(
__entry->flavor = flavor;
__entry->error = error;
+ __entry->keyring = key;
),
- TP_printk("flavor=%s error=%d",
- show_pseudoflavor(__entry->flavor), __entry->error)
+ TP_printk("flavor=%s error=%d keyring=%px",
+ show_pseudoflavor(__entry->flavor), __entry->error,
+ __entry->keyring)
);
TRACE_EVENT(rpcgss_oid_to_mech,
diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index fb75a883503f..972ca3c7385d 100644
--- a/net/sunrpc/auth.c
+++ b/net/sunrpc/auth.c
@@ -565,7 +565,7 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
if (test_bit(RPCAUTH_CRED_NEW, &cred->cr_flags) &&
cred->cr_ops->cr_init != NULL &&
!(flags & RPCAUTH_LOOKUP_NEW)) {
- int res = cred->cr_ops->cr_init(auth, cred);
+ int res = cred->cr_ops->cr_init(auth, cred, NULL);
if (res < 0) {
put_rpccred(cred);
cred = ERR_PTR(res);
@@ -683,11 +683,11 @@ rpcauth_bindcred(struct rpc_task *task, const struct cred *cred, int flags)
return 0;
}
-void
+bool
put_rpccred(struct rpc_cred *cred)
{
if (cred == NULL)
- return;
+ return false;
rcu_read_lock();
if (refcount_dec_and_test(&cred->cr_count))
goto destroy;
@@ -707,10 +707,11 @@ put_rpccred(struct rpc_cred *cred)
}
out:
rcu_read_unlock();
- return;
+ return false;
destroy:
rcu_read_unlock();
cred->cr_ops->crdestroy(cred);
+ return true;
}
EXPORT_SYMBOL_GPL(put_rpccred);
diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 1af71fbb0d80..f97cbf9655ca 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -28,12 +28,26 @@
#include <linux/sunrpc/gss_api.h>
#include <linux/uaccess.h>
#include <linux/hashtable.h>
+#include <linux/key.h>
+#include <linux/keyctl.h>
+#include <linux/key-type.h>
+#include <keys/user-type.h>
+#include <keys/request_key_auth-type.h>
#include "auth_gss_internal.h"
#include "../netns.h"
#include <trace/events/rpcgss.h>
+#define UINT_MAX_LEN 11
+static const char CLID_PREFIX[] = "clid:";
+static const char ID_PREFIX[] = "id:";
+static const char PRINC_PREFIX[] = "princ:";
+static const char PRINC_NONE[] = "princ:(none)";
+static struct key_type key_type_gss_cred;
+
+void gss_key_destroy(struct key *key);
+
static const struct rpc_authops authgss_ops;
static const struct rpc_credops gss_credops;
@@ -45,6 +59,8 @@ static unsigned int gss_expired_cred_retry_delay = GSS_RETRY_EXPIRED;
#define GSS_KEY_EXPIRE_TIMEO 240
static unsigned int gss_key_expire_timeo = GSS_KEY_EXPIRE_TIMEO;
+static bool use_keyring;
+
#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY RPCDBG_AUTH
#endif
@@ -98,6 +114,14 @@ struct gss_auth {
*/
struct gss_pipe *gss_pipe[2];
const char *target_name;
+ struct cred *keyring_cred;
+};
+
+struct gss_auxdata {
+ struct rpc_auth *auth;
+ struct auth_cred *acred;
+ int flags;
+ gfp_t gfp;
};
/* pipe_version >= 0 if and only if someone has a pipe open. */
@@ -174,7 +198,8 @@ gss_alloc_context(void)
#define GSSD_MIN_TIMEOUT (60 * 60)
static const void *
-gss_fill_context(const void *p, const void *end, struct gss_cl_ctx *ctx, struct gss_api_mech *gm)
+gss_fill_context(const void *p, const void *end, struct gss_cl_ctx *ctx,
+ struct gss_api_mech *gm, unsigned int *tout)
{
const void *q;
unsigned int seclen;
@@ -192,6 +217,7 @@ gss_fill_context(const void *p, const void *end, struct gss_cl_ctx *ctx, struct
goto err;
if (timeout == 0)
timeout = GSSD_MIN_TIMEOUT;
+ *tout = timeout;
ctx->gc_expiry = now + ((unsigned long)timeout * HZ);
/* Sequence number window. Determines the maximum number of
* simultaneous requests
@@ -267,6 +293,8 @@ struct gss_upcall_msg {
struct rpc_wait_queue rpc_waitqueue;
wait_queue_head_t waitqueue;
struct gss_cl_ctx *ctx;
+ struct key *authkey;
+ unsigned int timeout;
char databuf[UPCALL_BUF_LEN];
};
@@ -559,7 +587,8 @@ gss_alloc_msg(struct gss_auth *gss_auth,
}
static struct gss_upcall_msg *
-gss_setup_upcall(struct gss_auth *gss_auth, struct rpc_cred *cred)
+gss_setup_upcall(struct gss_auth *gss_auth, struct rpc_cred *cred,
+ struct key *authkey)
{
struct gss_cred *gss_cred = container_of(cred,
struct gss_cred, gc_base);
@@ -572,6 +601,7 @@ gss_setup_upcall(struct gss_auth *gss_auth, struct rpc_cred *cred)
gss_msg = gss_add_msg(gss_new);
if (gss_msg == gss_new) {
int res;
+ gss_msg->authkey = authkey;
refcount_inc(&gss_msg->count);
res = rpc_queue_upcall(gss_new->pipe, &gss_new->msg);
if (res) {
@@ -602,7 +632,7 @@ gss_refresh_upcall(struct rpc_task *task)
struct rpc_pipe *pipe;
int err = 0;
- gss_msg = gss_setup_upcall(gss_auth, cred);
+ gss_msg = gss_setup_upcall(gss_auth, cred, NULL);
if (PTR_ERR(gss_msg) == -EAGAIN) {
/* XXX: warning on the first, under the assumption we
* shouldn't normally hit this case on a refresh. */
@@ -638,16 +668,23 @@ gss_refresh_upcall(struct rpc_task *task)
}
static inline int
-gss_create_upcall(struct gss_auth *gss_auth, struct gss_cred *gss_cred)
+gss_create_upcall(struct gss_auth *gss_auth, struct gss_cred *gss_cred,
+ struct key *authkey)
{
struct net *net = gss_auth->net;
struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
struct rpc_pipe *pipe;
struct rpc_cred *cred = &gss_cred->gc_base;
struct gss_upcall_msg *gss_msg;
+ struct request_key_auth *rka;
+ struct key *key;
DEFINE_WAIT(wait);
int err;
+ if (use_keyring) {
+ rka = get_request_key_auth(authkey);
+ key = rka->target_key;
+ }
retry:
err = 0;
/* if gssd is down, just skip upcalling altogether */
@@ -656,7 +693,7 @@ gss_create_upcall(struct gss_auth *gss_auth, struct gss_cred *gss_cred)
err = -EACCES;
goto out;
}
- gss_msg = gss_setup_upcall(gss_auth, cred);
+ gss_msg = gss_setup_upcall(gss_auth, cred, authkey);
if (PTR_ERR(gss_msg) == -EAGAIN) {
err = wait_event_interruptible_timeout(pipe_version_waitqueue,
sn->pipe_version >= 0, 15 * HZ);
@@ -689,6 +726,17 @@ gss_create_upcall(struct gss_auth *gss_auth, struct gss_cred *gss_cred)
if (gss_msg->ctx) {
trace_rpcgss_ctx_init(gss_cred);
gss_cred_set_ctx(cred, gss_msg->ctx);
+ if (use_keyring) {
+ err = key_instantiate_and_link(key, gss_cred,
+ sizeof(gss_cred),
+ NULL, authkey);
+ if (!err) {
+ key_set_timeout(key, gss_msg->timeout);
+ err = key_link(gss_auth->keyring_cred->thread_keyring,
+ key);
+ }
+ complete_request_key(authkey, err);
+ }
} else {
err = gss_msg->msg.errno;
}
@@ -771,7 +819,8 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
list_del_init(&gss_msg->list);
spin_unlock(&pipe->lock);
- p = gss_fill_context(p, end, ctx, gss_msg->auth->mech);
+ p = gss_fill_context(p, end, ctx, gss_msg->auth->mech,
+ &gss_msg->timeout);
if (IS_ERR(p)) {
err = PTR_ERR(p);
switch (err) {
@@ -1032,6 +1081,8 @@ gss_create_new(const struct rpc_auth_create_args *args, struct rpc_clnt *clnt)
struct gss_pipe *gss_pipe;
struct rpc_auth * auth;
int err = -ENOMEM; /* XXX? */
+ struct cred *cred;
+ struct key *keyring;
if (!try_module_get(THIS_MODULE))
return ERR_PTR(err);
@@ -1094,7 +1145,34 @@ gss_create_new(const struct rpc_auth_create_args *args, struct rpc_clnt *clnt)
}
gss_auth->gss_pipe[0] = gss_pipe;
+ if (use_keyring) {
+ cred = prepare_kernel_cred(&init_task);
+ if (!cred) {
+ err = -ENOMEM;
+ goto err_destroy_pipe_0;
+ }
+ keyring = keyring_alloc("gss_keyring",
+ GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
+ (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+ KEY_USR_VIEW | KEY_USR_READ,
+ KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
+ if (IS_ERR(keyring)) {
+ err = PTR_ERR(keyring);
+ goto err_destroy_cred;
+ }
+ set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
+ cred->thread_keyring = keyring;
+ cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
+ gss_auth->keyring_cred = cred;
+ }
+
+ trace_rpcgss_createauth(flavor, err, gss_auth->keyring_cred ?
+ gss_auth->keyring_cred->thread_keyring : NULL);
return gss_auth;
+err_destroy_cred:
+ put_cred(cred);
+err_destroy_pipe_0:
+ gss_pipe_free(gss_auth->gss_pipe[0]);
err_destroy_pipe_1:
gss_pipe_free(gss_auth->gss_pipe[1]);
err_destroy_credcache:
@@ -1108,7 +1186,8 @@ gss_create_new(const struct rpc_auth_create_args *args, struct rpc_clnt *clnt)
kfree(gss_auth);
out_dec:
module_put(THIS_MODULE);
- trace_rpcgss_createauth(flavor, err);
+ trace_rpcgss_createauth(flavor, err, gss_auth->keyring_cred ?
+ gss_auth->keyring_cred->thread_keyring : NULL);
return ERR_PTR(err);
}
@@ -1139,6 +1218,19 @@ gss_put_auth(struct gss_auth *gss_auth)
kref_put(&gss_auth->kref, gss_free_callback);
}
+static bool gss_key_gc_iterator(void *object, void *__unused)
+{
+ struct key *key = keyring_ptr_to_key(object);
+ struct gss_cred *cred = key->payload.data[0];
+
+ if (cred && put_rpccred(&cred->gc_base)) {
+ key->payload.data[0] = NULL;
+ return false;
+ }
+ key_get(key);
+ return true;
+}
+
static void
gss_destroy(struct rpc_auth *auth)
{
@@ -1157,6 +1249,13 @@ gss_destroy(struct rpc_auth *auth)
gss_auth->gss_pipe[1] = NULL;
rpcauth_destroy_credcache(auth);
+ if (use_keyring) {
+ keyring_gc_custom(gss_auth->keyring_cred->thread_keyring,
+ &gss_key_gc_iterator, NULL);
+ key_revoke(gss_auth->keyring_cred->thread_keyring);
+ put_cred(gss_auth->keyring_cred);
+ }
+
gss_put_auth(gss_auth);
}
@@ -1369,14 +1468,109 @@ gss_hash_cred(struct auth_cred *acred, unsigned int hashbits)
return hash_64(from_kuid(&init_user_ns, acred->cred->fsuid), hashbits);
}
+static struct key *gss_request_key(struct rpc_auth *auth,
+ struct auth_cred *acred,
+ int flags, gfp_t gfp)
+{
+ struct gss_auth *gss_auth = container_of(auth, struct gss_auth, rpc_auth);
+ struct key *key;
+ struct gss_auxdata *aux;
+ char clid_str[UINT_MAX_LEN];
+ char id_str[UINT_MAX_LEN];
+ char *desc;
+ int clid_len, id_len, desclen;
+ struct key *dest_keyring;
+ key_ref_t keyref;
+
+ keyref = lookup_user_key(KEY_SPEC_USER_KEYRING,
+ KEY_LOOKUP_CREATE, KEY_NEED_SEARCH);
+ if (IS_ERR(keyref))
+ return ERR_CAST(keyref);
+ dest_keyring = key_ref_to_ptr(keyref);
+
+ clid_len = snprintf(clid_str, sizeof(clid_str), "%u",
+ gss_auth->client->cl_clid);
+ id_len = snprintf(id_str, sizeof(id_str), "%u",
+ from_kuid(&init_user_ns, acred->cred->fsuid));
+
+ desclen = sizeof(CLID_PREFIX) + clid_len + 1 +
+ sizeof(ID_PREFIX) + id_len;
+
+ if (acred->principal)
+ desclen += (1 + sizeof(PRINC_PREFIX) + strlen(acred->principal));
+ else
+ desclen += (1 + sizeof(PRINC_NONE));
+
+ desc = kmalloc(desclen, GFP_KERNEL);
+ if (!desc)
+ return ERR_PTR(-ENOMEM);
+
+ if (acred->principal)
+ sprintf(desc, "%s%s %s%s %s%s", CLID_PREFIX, clid_str,
+ ID_PREFIX, id_str, PRINC_PREFIX, acred->principal);
+ else
+ sprintf(desc, "%s%s %s%s %s", CLID_PREFIX, clid_str,
+ ID_PREFIX, id_str, PRINC_NONE);
+
+ aux = kzalloc(sizeof(*aux), gfp);
+ if (!aux)
+ return ERR_PTR(-ENOMEM);
+
+ aux->auth = auth;
+ aux->acred = acred;
+ aux->flags = flags;
+ aux->gfp = gfp;
+
+ key = request_key_with_auxdata(&key_type_gss_cred, desc,
+ NULL, "", 0, aux, dest_keyring);
+ kfree(aux);
+ kfree(desc);
+ return key;
+}
+
+static struct rpc_cred *
+gss_lookup_keyring(struct rpc_auth *auth, struct auth_cred *acred,
+ int flags, gfp_t gfp)
+{
+ struct key *key;
+ struct gss_cred *gss_cred;
+ struct rpc_cred *cred = NULL;
+ const struct cred *saved_cred;
+
+ saved_cred = override_creds(acred->cred);
+ key = gss_request_key(auth, acred, flags, rpc_task_gfp_mask());
+ trace_rpcgss_request_key_result(acred, key);
+ if (IS_ERR(key)) {
+ cred = ERR_CAST(key);
+ goto out;
+ }
+ down_read(&key->sem);
+ gss_cred = key->payload.data[0];
+ if (!gss_cred) {
+ cred = ERR_PTR(-ENOKEY);
+ goto out_up;
+ }
+ cred = get_rpccred(&gss_cred->gc_base);
+out_up:
+ up_read(&key->sem);
+ key_put(key);
+out:
+ revert_creds(saved_cred);
+ return cred;
+}
+
/*
* Lookup RPCSEC_GSS cred for the current process
*/
static struct rpc_cred *gss_lookup_cred(struct rpc_auth *auth,
struct auth_cred *acred, int flags)
{
- return rpcauth_lookup_credcache(auth, acred, flags,
- rpc_task_gfp_mask());
+ if (use_keyring)
+ return gss_lookup_keyring(auth, acred, flags,
+ rpc_task_gfp_mask());
+ else
+ return rpcauth_lookup_credcache(auth, acred, flags,
+ rpc_task_gfp_mask());
}
static struct rpc_cred *
@@ -1405,18 +1599,128 @@ gss_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags, gfp_t
}
static int
-gss_cred_init(struct rpc_auth *auth, struct rpc_cred *cred)
+gss_cred_init(struct rpc_auth *auth, struct rpc_cred *cred, struct key *authkey)
{
struct gss_auth *gss_auth = container_of(auth, struct gss_auth, rpc_auth);
struct gss_cred *gss_cred = container_of(cred,struct gss_cred, gc_base);
int err;
do {
- err = gss_create_upcall(gss_auth, gss_cred);
+ err = gss_create_upcall(gss_auth, gss_cred, authkey);
} while (err == -EAGAIN);
return err;
}
+static bool gss_cmp(const struct key *key,
+ const struct key_match_data *match_data)
+{
+ struct gss_cred *gss_cred = rcu_dereference(key->payload.rcu_data0);
+ struct rpc_cred *rc;
+ struct gss_cl_ctx *ctx;
+ bool ret;
+
+ if (!gss_cred)
+ return false;
+
+ rc = &gss_cred->gc_base;
+
+ if (test_bit(RPCAUTH_CRED_NEW, &rc->cr_flags))
+ goto out;
+ /* Don't match with creds that have expired. */
+ ctx = rcu_dereference(gss_cred->gc_ctx);
+ if (!ctx || time_after(jiffies, ctx->gc_expiry)) {
+ rcu_read_unlock();
+ return false;
+ }
+ if (!test_bit(RPCAUTH_CRED_UPTODATE, &rc->cr_flags)) {
+ return false;
+ }
+out:
+ ret = strcmp(key->description, match_data->raw_data) == 0;
+ return ret;
+}
+
+static int gss_match_preparse(struct key_match_data *match_data)
+{
+ match_data->cmp = gss_cmp;
+ match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
+ return 0;
+}
+
+static int gss_request_key_upcall(struct key *authkey, void *aux)
+{
+ struct gss_auxdata *data = aux;
+ struct rpc_auth *auth = data->auth;
+ struct auth_cred *acred = data->acred;
+ int flags = data->flags;
+ gfp_t gfp = data->gfp;
+ struct rpc_cred *cred;
+ int ret;
+
+ cred = gss_create_cred(auth, acred, flags, gfp);
+ if (IS_ERR(cred)) {
+ ret = PTR_ERR(cred);
+ complete_request_key(authkey, ret);
+ return ret;
+ }
+
+ ret = gss_cred_init(auth, cred, authkey);
+ if (ret < 0) {
+ complete_request_key(authkey, ret);
+ }
+
+ return ret;
+}
+
+void gss_key_revoke(struct key *key)
+{
+ struct gss_cred *cred = key->payload.data[0];
+
+ if (cred && put_rpccred(&cred->gc_base))
+ key->payload.data[0] = NULL;
+}
+
+void gss_key_destroy(struct key *key)
+{
+ struct gss_cred *cred = key->payload.data[0];
+
+ if (cred && put_rpccred(&cred->gc_base))
+ key->payload.data[0] = NULL;
+}
+
+void gss_describe(const struct key *key, struct seq_file *m)
+{
+ struct gss_cred *gss_cred = key->payload.data[0];
+
+ if (!gss_cred)
+ return;
+
+ seq_puts(m, key->description);
+ if (key_is_positive(key)) {
+ seq_printf(m, " gc: %px", gss_cred);
+ }
+}
+
+int gss_key_instantiate(struct key *key, struct key_preparsed_payload *prep)
+{
+ if (prep->datalen != key->type->def_datalen)
+ return -EINVAL;
+
+ rcu_assign_keypointer(key, (struct gss_cred *)prep->data);
+ return 0;
+}
+
+static struct key_type key_type_gss_cred = {
+ .name = "gss_cred",
+ .def_datalen = sizeof(struct gss_cred *),
+ .instantiate = gss_key_instantiate,
+ .match_preparse = gss_match_preparse,
+ .revoke = gss_key_revoke,
+ .destroy = gss_key_destroy,
+ .describe = gss_describe,
+ .request_key = gss_request_key_upcall,
+};
+
static char *
gss_stringify_acceptor(struct rpc_cred *cred)
{
@@ -2261,6 +2565,11 @@ static int __init init_rpcsec_gss(void)
err = register_pernet_subsys(&rpcsec_gss_net_ops);
if (err)
goto out_svc_exit;
+ if (use_keyring) {
+ err = register_key_type(&key_type_gss_cred);
+ if (err)
+ goto out_svc_exit;
+ }
rpc_init_wait_queue(&pipe_version_rpc_waitqueue, "gss pipe version");
return 0;
out_svc_exit:
@@ -2273,6 +2582,8 @@ static int __init init_rpcsec_gss(void)
static void __exit exit_rpcsec_gss(void)
{
+ if (use_keyring)
+ unregister_key_type(&key_type_gss_cred);
unregister_pernet_subsys(&rpcsec_gss_net_ops);
gss_svc_shutdown();
rpcauth_unregister(&authgss_ops);
@@ -2294,5 +2605,10 @@ MODULE_PARM_DESC(key_expire_timeo, "Time (in seconds) at the end of a "
"credential keys lifetime where the NFS layer cleans up "
"prior to key expiration");
+module_param(use_keyring, bool, 0444);
+MODULE_PARM_DESC(use_keyring,
+ "Store credentials in keyrings instead of credential cache. "
+ "Default: false");
+
module_init(init_rpcsec_gss)
module_exit(exit_rpcsec_gss)
--
2.39.2
We want to store GSS creds in user keyrings. Make
search_cred_keyrings_rcu() search the user keyring if it exists so that
keys containing GSS creds will be found.
Signed-off-by: Scott Mayhew <[email protected]>
---
security/keys/internal.h | 1 +
security/keys/process_keys.c | 78 ++++++++++++++++++++++++++++++------
2 files changed, 67 insertions(+), 12 deletions(-)
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 3c1e7122076b..524178802406 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -149,6 +149,7 @@ extern key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx)
extern struct key *find_keyring_by_name(const char *name, bool uid_keyring);
extern int look_up_user_keyrings(struct key **, struct key **);
+extern struct key *get_user_keyring_rcu(const struct cred *);
extern struct key *get_user_session_keyring_rcu(const struct cred *);
extern int install_thread_keyring_to_cred(struct cred *);
extern int install_process_keyring_to_cred(struct cred *);
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index b5d5333ab330..c78b13a0c5a2 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -179,13 +179,12 @@ int look_up_user_keyrings(struct key **_user_keyring,
}
/*
- * Get the user session keyring if it exists, but don't create it if it
- * doesn't.
+ * Get a keyring if it exists, but don't create it if it doesn't.
*/
-struct key *get_user_session_keyring_rcu(const struct cred *cred)
+static struct key *get_keyring_rcu(const struct cred *cred, key_serial_t id)
{
struct key *reg_keyring = READ_ONCE(cred->user_ns->user_keyring_register);
- key_ref_t session_keyring_r;
+ key_ref_t keyring_r;
char buf[20];
struct keyring_search_context ctx = {
@@ -201,15 +200,47 @@ struct key *get_user_session_keyring_rcu(const struct cred *cred)
if (!reg_keyring)
return NULL;
- ctx.index_key.desc_len = snprintf(buf, sizeof(buf), "_uid_ses.%u",
- from_kuid(cred->user_ns,
- cred->user->uid));
+ switch (id) {
+ case KEY_SPEC_USER_KEYRING:
+ ctx.index_key.desc_len = snprintf(buf, sizeof(buf),
+ "_uid.%u",
+ from_kuid(cred->user_ns,
+ cred->user->uid));
+ break;
+ case KEY_SPEC_USER_SESSION_KEYRING:
+ ctx.index_key.desc_len = snprintf(buf, sizeof(buf),
+ "_uid_ses.%u",
+ from_kuid(cred->user_ns,
+ cred->user->uid));
+ break;
+ default:
+ return NULL;
+ break;
+ }
- session_keyring_r = keyring_search_rcu(make_key_ref(reg_keyring, true),
- &ctx);
- if (IS_ERR(session_keyring_r))
+ keyring_r = keyring_search_rcu(make_key_ref(reg_keyring, true), &ctx);
+
+ if (IS_ERR(keyring_r))
return NULL;
- return key_ref_to_ptr(session_keyring_r);
+ return key_ref_to_ptr(keyring_r);
+}
+
+/*
+ * Get the user keyring if it exists, but don't create it if it
+ * doesn't.
+ */
+struct key *get_user_keyring_rcu(const struct cred *cred)
+{
+ return get_keyring_rcu(cred, KEY_SPEC_USER_KEYRING);
+}
+
+/*
+ * Get the user session keyring if it exists, but don't create it if it
+ * doesn't.
+ */
+struct key *get_user_session_keyring_rcu(const struct cred *cred)
+{
+ return get_keyring_rcu(cred, KEY_SPEC_USER_SESSION_KEYRING);
}
/*
@@ -421,7 +452,7 @@ void key_fsgid_changed(struct cred *new_cred)
*/
key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
{
- struct key *user_session;
+ struct key *user_session, *user;
key_ref_t key_ref, ret, err;
const struct cred *cred = ctx->cred;
@@ -519,6 +550,29 @@ key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
}
}
+ /* search the user keyring */
+ if ((user = get_user_keyring_rcu(cred))) {
+ key_ref = keyring_search_rcu(make_key_ref(user, 1),
+ ctx);
+ key_put(user);
+
+ if (!IS_ERR(key_ref))
+ goto found;
+
+ switch (PTR_ERR(key_ref)) {
+ case -EAGAIN: /* no key */
+ if (ret)
+ break;
+ fallthrough;
+ case -ENOKEY: /* negative key */
+ ret = key_ref;
+ break;
+ default:
+ err = key_ref;
+ break;
+ }
+ }
+
/* no key - decide on the error we're going to go for */
key_ref = ret ? ret : err;
--
2.39.2
On Thu, Apr 20, 2023 at 16:20:04 -0400, Scott Mayhew wrote:
> This patch adds the option to store GSS credentials in keyrings as an
> alternative to the RPC credential cache, to give users the ability to
> destroy their GSS credentials on demand via 'keyctl unlink'.
Can documentation please be added to `Documentation/security/keys` about
this key type?
> Summary of the changes:
>
> - Added key_type key_type_gss_cred and associated functions. The
> request_key function makes use of the existing upcall mechanism to
> gssd.
>
> - Added a keyring to the gss_auth struct to allow all of the assocated
> GSS credentials to be destroyed on RPC client shutdown (when the
> filesystem is unmounted).
>
> - The key description contains the RPC client id, the user id, and the
> principal (for machine creds).
What is the format of this within the bytes?
> - The key payload contains the address of the gss_cred.
What is the format of this within the bytes?
> - The key is linked to the user's user keyring (KEY_SPEC_USER_KEYRING)
> as well as to the keyring on the gss_auth struct.
Where is this documented? Can the key be moved later?
> - gss_cred_init() now takes an optional pointer to an authkey, which is
> passed down to gss_create_upcall() and gss_setup_upcall(), where it is
> added to the gss_msg. This is used for complete_request_key() after
> the upcall is done.
>
> - put_rpccred() now returns a bool to indicate whether it called
> crdestroy(), and is used by gss_key_revoke() and gss_key_destroy() to
> determine whether to clear the key payload.
>
> - gss_fill_context() now returns the GSS context's timeout via the tout
> parameter, which is used to set the timeout of the key.
>
> - Added the module parameter 'use_keyring'. When set to true, the GSS
> credentials are stored in the keyrings. When false, the GSS
> credentials are stored in the RPC credential caches.
>
> - Added a tracepoint to log the result of the key request, which prints
> either the key serial or an error return value.
>
> Signed-off-by: Scott Mayhew <[email protected]>
> ---
> include/linux/sunrpc/auth.h | 4 +-
> include/trace/events/rpcgss.h | 46 ++++-
> net/sunrpc/auth.c | 9 +-
> net/sunrpc/auth_gss/auth_gss.c | 338 +++++++++++++++++++++++++++++++--
> 4 files changed, 376 insertions(+), 21 deletions(-)
Thanks,
--Ben
On Sat, 22 Apr 2023, Ben Boeckel wrote:
> On Thu, Apr 20, 2023 at 16:20:04 -0400, Scott Mayhew wrote:
> > This patch adds the option to store GSS credentials in keyrings as an
> > alternative to the RPC credential cache, to give users the ability to
> > destroy their GSS credentials on demand via 'keyctl unlink'.
>
> Can documentation please be added to `Documentation/security/keys` about
> this key type?
I'll work on that.
>
> > Summary of the changes:
> >
> > - Added key_type key_type_gss_cred and associated functions. The
> > request_key function makes use of the existing upcall mechanism to
> > gssd.
> >
> > - Added a keyring to the gss_auth struct to allow all of the assocated
> > GSS credentials to be destroyed on RPC client shutdown (when the
> > filesystem is unmounted).
> >
> > - The key description contains the RPC client id, the user id, and the
> > principal (for machine creds).
>
> What is the format of this within the bytes?
The format is "clid: <client-id> id: <fsuid> princ:<princ>", where
client-id and fsuid are unsigned ints and princ is either "(none)" or
"*" if it's a machine cred:
crash> p ((struct key *) 0xffff8b4410197900)->description
$1 = 0xffff8b4446cbd740 "clid:1 id:1000 princ:(none)"
>
> > - The key payload contains the address of the gss_cred.
>
> What is the format of this within the bytes?
The payload is just a pointer:
crash> p ((struct key *) 0xffff8b4410197900)->payload.data[0]
$2 = (void *) 0xffff8b44381cd480
>
> > - The key is linked to the user's user keyring (KEY_SPEC_USER_KEYRING)
> > as well as to the keyring on the gss_auth struct.
>
> Where is this documented? Can the key be moved later?
It's not - I can add that to the documentation for the new key type.
The key should not be moved. I haven't tested if it's possible to move
it, but it's something that we'd want to disallow.
-Scott
>
> > - gss_cred_init() now takes an optional pointer to an authkey, which is
> > passed down to gss_create_upcall() and gss_setup_upcall(), where it is
> > added to the gss_msg. This is used for complete_request_key() after
> > the upcall is done.
> >
> > - put_rpccred() now returns a bool to indicate whether it called
> > crdestroy(), and is used by gss_key_revoke() and gss_key_destroy() to
> > determine whether to clear the key payload.
> >
> > - gss_fill_context() now returns the GSS context's timeout via the tout
> > parameter, which is used to set the timeout of the key.
> >
> > - Added the module parameter 'use_keyring'. When set to true, the GSS
> > credentials are stored in the keyrings. When false, the GSS
> > credentials are stored in the RPC credential caches.
> >
> > - Added a tracepoint to log the result of the key request, which prints
> > either the key serial or an error return value.
> >
> > Signed-off-by: Scott Mayhew <[email protected]>
> > ---
> > include/linux/sunrpc/auth.h | 4 +-
> > include/trace/events/rpcgss.h | 46 ++++-
> > net/sunrpc/auth.c | 9 +-
> > net/sunrpc/auth_gss/auth_gss.c | 338 +++++++++++++++++++++++++++++++--
> > 4 files changed, 376 insertions(+), 21 deletions(-)
>
> Thanks,
>
> --Ben
>
On Mon, Apr 24, 2023 at 10:02:25 -0400, Scott Mayhew wrote:
> On Sat, 22 Apr 2023, Ben Boeckel wrote:
> > What is the format of this within the bytes?
>
> The format is "clid: <client-id> id: <fsuid> princ:<princ>", where
> client-id and fsuid are unsigned ints and princ is either "(none)" or
> "*" if it's a machine cred:
>
> crash> p ((struct key *) 0xffff8b4410197900)->description
> $1 = 0xffff8b4446cbd740 "clid:1 id:1000 princ:(none)"
Thanks. A bit annoying to parse, but doable.
> > > - The key payload contains the address of the gss_cred.
> >
> > What is the format of this within the bytes?
>
> The payload is just a pointer:
>
> crash> p ((struct key *) 0xffff8b4410197900)->payload.data[0]
> $2 = (void *) 0xffff8b44381cd480
This looks less useful to userspace (beyond some kind of unique
ID…though can it be used to extract information about ASLR or any other
security mechanism?). Can userspace somehow write to this payload to
confuse things at all?
I'm no security expert so this is just a "random idea" to at least
hopefully trigger Cunningham's Law, but storing it `xor`'d with some
per-boot secret could help muddle any information
leak/extraction/targeting usefulness.
> > > - The key is linked to the user's user keyring (KEY_SPEC_USER_KEYRING)
> > > as well as to the keyring on the gss_auth struct.
> >
> > Where is this documented? Can the key be moved later?
>
> It's not - I can add that to the documentation for the new key type.
> The key should not be moved. I haven't tested if it's possible to move
> it, but it's something that we'd want to disallow.
If it shouldn't be unlinked that's one thing, there's still the
possibility of also linking it from another keyring (I don't see why
that should be a problem at least).
Also, to be clear I was talking about the `KEY_SPEC_USER_KEYRING`
keyring. Keeping it in the `gss_auth`'s keyring makes 100% sense (though
if there's no way to keep it there, that seems like a corner case that
would need considered).
Thanks,
--Ben
On Mon, 24 Apr 2023, Ben Boeckel wrote:
> On Mon, Apr 24, 2023 at 10:02:25 -0400, Scott Mayhew wrote:
> > On Sat, 22 Apr 2023, Ben Boeckel wrote:
> > > What is the format of this within the bytes?
> >
> > The format is "clid: <client-id> id: <fsuid> princ:<princ>", where
> > client-id and fsuid are unsigned ints and princ is either "(none)" or
> > "*" if it's a machine cred:
> >
> > crash> p ((struct key *) 0xffff8b4410197900)->description
> > $1 = 0xffff8b4446cbd740 "clid:1 id:1000 princ:(none)"
>
> Thanks. A bit annoying to parse, but doable.
>
> > > > - The key payload contains the address of the gss_cred.
> > >
> > > What is the format of this within the bytes?
> >
> > The payload is just a pointer:
> >
> > crash> p ((struct key *) 0xffff8b4410197900)->payload.data[0]
> > $2 = (void *) 0xffff8b44381cd480
>
> This looks less useful to userspace (beyond some kind of unique
> ID…though can it be used to extract information about ASLR or any other
> security mechanism?). Can userspace somehow write to this payload to
> confuse things at all?
>
> I'm no security expert so this is just a "random idea" to at least
> hopefully trigger Cunningham's Law, but storing it `xor`'d with some
> per-boot secret could help muddle any information
> leak/extraction/targeting usefulness.
Just to be clear, this isn't meant to be written or read by userspace.
The user isn't explicitly requesting the creation of a key with the
gss_cred key type. It happens automatically when they access an NFS
filesystem mounted with "sec=krb5{,i,p}", using the existing upcall
mechanism to rpc.gssd. The only difference is that instead of sticking
the resulting gss_cred in the rpc_auth.au_credcache hash table, we're
now creating a key with the address of the gss_cred and storing it in
keyrings.
Note that I didn't even provide a 'read' method for this key type
because the payload isn't intended to be read by users. However, in the
past some users have requested a 'whoami' type function so they could see
what kerberos principal was used to establish the GSS context. I was
thinking that would be useful information to output in a 'read' method,
however that information is not currently in the kernel - rpc.gssd would
need to add the initiator principal to the information it writes in the
downcall to the kernel, and I haven't really looked yet to see if it's
feasible to do that without breaking the existing upcall mechanism.
Also, while I'm currently printing some raw addresses in the tracepoints
as well is in the /proc/keys output for this new key type, that is
strictly for my own debugging purposes and that stuff will ultimately be
removed in the final patches.
>
> > > > - The key is linked to the user's user keyring (KEY_SPEC_USER_KEYRING)
> > > > as well as to the keyring on the gss_auth struct.
> > >
> > > Where is this documented? Can the key be moved later?
> >
> > It's not - I can add that to the documentation for the new key type.
> > The key should not be moved. I haven't tested if it's possible to move
> > it, but it's something that we'd want to disallow.
>
> If it shouldn't be unlinked that's one thing, there's still the
> possibility of also linking it from another keyring (I don't see why
> that should be a problem at least).
>
> Also, to be clear I was talking about the `KEY_SPEC_USER_KEYRING`
> keyring. Keeping it in the `gss_auth`'s keyring makes 100% sense (though
> if there's no way to keep it there, that seems like a corner case that
> would need considered).
We definitely allow unlinking - that's sort of the whole point because
it allows users to establish a new GSS credential (most likely with a
different initiator principal that the old one).
It doesn't really make sense for the key to be on any other keyring besides
the user keyring. If it were on the session keyring, and if you were
logged into multiple sessions, then those sessions would be constantly
whacking each others GSS creds and they be constantly
creating/destroying new GSS creds with the NFS server.
Having them on the session keyring also presents another problem because
the NFS client caches NFSv4 open owners, which take a reference on a
struct cred. When you log out, pam_keyinit revokes the session keying.
If you log back in and try to resume NFS access (generating a new key),
the current request key code will find the cred with the revoked session
keyring, and it will try to link the new key to that revoked session
keyring, which will then fail with -EKEYREVOKED. That's the reason
for patches 3/5 and 4/5, to allow request_key_with_auxdata() to link the
key directly to the user keyring.
-Scott
>
> Thanks,
>
> --Ben
>
On Mon, Apr 24, 2023 at 11:01:58 -0400, Scott Mayhew wrote:
> Just to be clear, this isn't meant to be written or read by userspace.
> The user isn't explicitly requesting the creation of a key with the
> gss_cred key type. It happens automatically when they access an NFS
> filesystem mounted with "sec=krb5{,i,p}", using the existing upcall
> mechanism to rpc.gssd. The only difference is that instead of sticking
> the resulting gss_cred in the rpc_auth.au_credcache hash table, we're
> now creating a key with the address of the gss_cred and storing it in
> keyrings.
Ah, ok. I'm mostly interested in the userspace side as the author of
https://github.com/mathstuf/rust-keyutils which I try to keep some safe
wrappers around various keytypes.
> We definitely allow unlinking - that's sort of the whole point because
> it allows users to establish a new GSS credential (most likely with a
> different initiator principal that the old one).
>
> It doesn't really make sense for the key to be on any other keyring besides
> the user keyring. If it were on the session keyring, and if you were
> logged into multiple sessions, then those sessions would be constantly
> whacking each others GSS creds and they be constantly
> creating/destroying new GSS creds with the NFS server.
>
> Having them on the session keyring also presents another problem because
> the NFS client caches NFSv4 open owners, which take a reference on a
> struct cred. When you log out, pam_keyinit revokes the session keying.
> If you log back in and try to resume NFS access (generating a new key),
> the current request key code will find the cred with the revoked session
> keyring, and it will try to link the new key to that revoked session
> keyring, which will then fail with -EKEYREVOKED. That's the reason
> for patches 3/5 and 4/5, to allow request_key_with_auxdata() to link the
> key directly to the user keyring.
Ok. These lifetime things definitely deserve docs.
Thanks,
--Ben