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Subject[PATCH] nfs/keys/idmap: intermittent erroneous uid/gid bug
Hi,

I am investigating this bug:
https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/1124250
which is also:
https://bugzilla.redhat.com/show_bug.cgi?id=876705
and:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=758870

After the keys which map NFS uid/gid to names expire there is sometimes a
delay in them being recreated. I believe this is because
nfs_idmap_request_key calls request_key_with_auxdata which returns expired
keys if they exist. If this happens there is no-one to re-create the key.

I think, instead, nfs_idmap_request_key should request a new key with a
userspace upcall if its key for a particular name has expired.

I have made the attached patch which fixes the problem in my tests. It
adds request_valid_key_with_auxdata() which does the same as
request_key_with_auxdata() except that it ignores expired, revoked and
invalidated keys. It does this by passing KEYRING_SEARCH_DO_STATE_CHECK
into the context for search_process_keyrings inside request_key_and_link.
If all keys are expired, this function then asks userspace for an updated
key.

I have no previous experience in the kernel, so please be gentle :) I am
happy to change and re-test the patch to anyone's whim.

Thanks & best regards,
Carl

Signed-off-by: Carl Hetherington <cth@carlh.net>
---
diff --git a/fs/nfs/idmap.c b/fs/nfs/idmap.c
index 567983d..744e40f 100644
--- a/fs/nfs/idmap.c
+++ b/fs/nfs/idmap.c
@@ -278,8 +278,8 @@ static struct key *nfs_idmap_request_key(const char
*name, size_t namelen,
rkey = request_key(&key_type_id_resolver, desc, "");
if (IS_ERR(rkey)) {
mutex_lock(&idmap->idmap_mutex);
- rkey = request_key_with_auxdata(&key_type_id_resolver_legacy,
- desc, "", 0, idmap);
+ rkey = request_valid_key_with_auxdata(&key_type_id_resolver_legacy,
+ desc, "", 0, idmap);
mutex_unlock(&idmap->idmap_mutex);
}

diff --git a/include/linux/key.h b/include/linux/key.h
index 80d6774..6a4ef03 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -252,6 +252,12 @@ extern struct key *request_key_with_auxdata(struct
key_type *type,
size_t callout_len,
void *aux);

+extern struct key *request_valid_key_with_auxdata(struct key_type *type,
+ const char *description,
+ const void *callout_info,
+ size_t callout_len,
+ void *aux);
+
extern struct key *request_key_async(struct key_type *type,
const char *description,
const void *callout_info,
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 80b2aac..5c9bc62 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -150,7 +150,8 @@ extern struct key *request_key_and_link(struct
key_type *type,
size_t callout_len,
void *aux,
struct key *dest_keyring,
- unsigned long flags);
+ unsigned long key_alloc_flags,
+ unsigned long
keyring_search_flags);

extern int lookup_user_key_possessed(const struct key *key, const void *target);
extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index cee72ce..25a12bc 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -212,7 +212,7 @@ SYSCALL_DEFINE4(request_key, const char __user *, _type,
/* do the search */
key = request_key_and_link(ktype, description, callout_info,
callout_len, NULL, key_ref_to_ptr(dest_ref),
- KEY_ALLOC_IN_QUOTA);
+ KEY_ALLOC_IN_QUOTA, 0);
if (IS_ERR(key)) {
ret = PTR_ERR(key);
goto error5;
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 3814119..af8345c 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -500,7 +500,11 @@ couldnt_alloc_key:
* @callout_len: The length of callout_info.
* @aux: Auxiliary data for the upcall.
* @dest_keyring: Where to cache the key.
- * @flags: Flags to key_alloc().
+ * @key_alloc_flags: Flags to key_alloc().
+ * @keyring_search_flags: Flags to pass in the keyring search context
+ * (in addition to KEYRING_SEARCH_LOOKUP_DIRECT). For example, passing
+ * KEYRING_SEARCH_DO_STATE_CHECK here will stop the function returning
+ * invalidated, revoked or expired keys.
*
* A key matching the specified criteria is searched for in the process's
* keyrings and returned with its usage count incremented if found.
Otherwise,
@@ -525,7 +529,8 @@ struct key *request_key_and_link(struct key_type *type,
size_t callout_len,
void *aux,
struct key *dest_keyring,
- unsigned long flags)
+ unsigned long key_alloc_flags,
+ unsigned long keyring_search_flags)
{
struct keyring_search_context ctx = {
.index_key.type = type,
@@ -533,7 +538,7 @@ struct key *request_key_and_link(struct key_type *type,
.cred = current_cred(),
.match = type->match,
.match_data = description,
- .flags = KEYRING_SEARCH_LOOKUP_DIRECT,
+ .flags = KEYRING_SEARCH_LOOKUP_DIRECT | keyring_search_flags
};
struct key *key;
key_ref_t key_ref;
@@ -541,7 +546,7 @@ struct key *request_key_and_link(struct key_type *type,

kenter("%s,%s,%p,%zu,%p,%p,%lx",
ctx.index_key.type->name, ctx.index_key.description,
- callout_info, callout_len, aux, dest_keyring, flags);
+ callout_info, callout_len, aux, dest_keyring, key_alloc_flags);

/* search all the process keyrings for a key */
key_ref = search_process_keyrings(&ctx);
@@ -568,7 +573,7 @@ struct key *request_key_and_link(struct key_type *type,
goto error;

key = construct_key_and_link(&ctx, callout_info, callout_len,
- aux, dest_keyring, flags);
+ aux, dest_keyring,
key_alloc_flags);
}

error:
@@ -629,7 +634,7 @@ struct key *request_key(struct key_type *type,
if (callout_info)
callout_len = strlen(callout_info);
key = request_key_and_link(type, description, callout_info,
callout_len,
- NULL, NULL, KEY_ALLOC_IN_QUOTA);
+ NULL, NULL, KEY_ALLOC_IN_QUOTA, 0);
if (!IS_ERR(key)) {
ret = wait_for_key_construction(key, false);
if (ret < 0) {
@@ -665,7 +670,7 @@ struct key *request_key_with_auxdata(struct key_type
*type,
int ret;

key = request_key_and_link(type, description, callout_info,
callout_len,
- aux, NULL, KEY_ALLOC_IN_QUOTA);
+ aux, NULL, KEY_ALLOC_IN_QUOTA, 0);
if (!IS_ERR(key)) {
ret = wait_for_key_construction(key, false);
if (ret < 0) {
@@ -677,6 +682,42 @@ struct key *request_key_with_auxdata(struct key_type
*type,
}
EXPORT_SYMBOL(request_key_with_auxdata);

+/**
+ * request_valid_key_with_auxdata - Request a key with auxiliary data for the upcaller
+ * @type: The type of key we want.
+ * @description: The searchable description of the key.
+ * @callout_info: The data to pass to the instantiation upcall (or NULL).
+ * @callout_len: The length of callout_info.
+ * @aux: Auxiliary data for the upcall.
+ *
+ * As for request_key_with_auxdata() except that existing invalidated, revoked and expired
+ * keys are ignored during the search for the requested key.
+ *
+ * Furthermore, it then works as wait_for_key_construction() to wait for the
+ * completion of keys undergoing construction with a non-interruptible wait.
+ */
+struct key *request_valid_key_with_auxdata(struct key_type *type,
+ const char *description,
+ const void *callout_info,
+ size_t callout_len,
+ void *aux)
+{
+ struct key *key;
+ int ret;
+
+ key = request_key_and_link(type, description, callout_info, callout_len,
+ aux, NULL, KEY_ALLOC_IN_QUOTA, KEYRING_SEARCH_DO_STATE_CHECK);
+ if (!IS_ERR(key)) {
+ ret = wait_for_key_construction(key, false);
+ if (ret < 0) {
+ key_put(key);
+ return ERR_PTR(ret);
+ }
+ }
+ return key;
+}
+EXPORT_SYMBOL(request_valid_key_with_auxdata);
+
/*
* request_key_async - Request a key (allow async construction)
* @type: Type of key.
@@ -698,7 +739,7 @@ struct key *request_key_async(struct key_type *type,
{
return request_key_and_link(type, description, callout_info,
callout_len, NULL, NULL,
- KEY_ALLOC_IN_QUOTA);
+ KEY_ALLOC_IN_QUOTA, 0);
}
EXPORT_SYMBOL(request_key_async);

@@ -723,6 +764,6 @@ struct key *request_key_async_with_auxdata(struct
key_type *type,
void *aux)
{
return request_key_and_link(type, description, callout_info,
- callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA);
+ callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA, 0);
}
EXPORT_SYMBOL(request_key_async_with_auxdata);


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