system/qemu
system/qemu
1
0
Fork 0
mirror of https://gitlab.com/qemu-project/qemu synced 2024-11-05 20:35:44 +00:00
Code Issues Projects Releases Packages Wiki Activity

hw/xen: Implement XenStore permissions

Browse source 
Store perms as a GList of strings, check permissions.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
This commit is contained in:
Paul Durrant 2023-01-23 16:21:16 +00:00 committed by David Woodhouse
parent 7cabbdb70d
commit be1934dfef
4 changed files with 275 additions and 21 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
hw/i386/kvm/xen_xenstore.c
View file

@ -98,7 +98,7 @@ static void xen_xenstore_realize(DeviceState *dev, Error **errp)
aio_set_fd_handler(qemu_get_aio_context(), xen_be_evtchn_fd(s->eh), true,
xen_xenstore_event, NULL, NULL, NULL, s);
s->impl = xs_impl_create();
s->impl = xs_impl_create(xen_domid);
}
static bool xen_xenstore_is_needed(void *opaque)

259
hw/i386/kvm/xenstore_impl.c
View file

@ -12,6 +12,8 @@
#include "qemu/osdep.h"
#include "qom/object.h"
#include "hw/xen/xen.h"
#include "xen_xenstore.h"
#include "xenstore_impl.h"
@ -30,6 +32,7 @@
typedef struct XsNode {
uint32_t ref;
GByteArray *content;
GList *perms;
GHashTable *children;
uint64_t gencnt;
bool deleted_in_tx;
@ -133,6 +136,9 @@ static inline void xs_node_unref(XsNode *n)
if (n->content) {
g_byte_array_unref(n->content);
}
if (n->perms) {
g_list_free_full(n->perms, g_free);
}
if (n->children) {
g_hash_table_unref(n->children);
}
@ -144,8 +150,51 @@ static inline void xs_node_unref(XsNode *n)
g_free(n);
}
char *xs_perm_as_string(unsigned int perm, unsigned int domid)
{
char letter;
switch (perm) {
case XS_PERM_READ | XS_PERM_WRITE:
letter = 'b';
break;
case XS_PERM_READ:
letter = 'r';
break;
case XS_PERM_WRITE:
letter = 'w';
break;
case XS_PERM_NONE:
default:
letter = 'n';
break;
}
return g_strdup_printf("%c%u", letter, domid);
}
static gpointer do_perm_copy(gconstpointer src, gpointer user_data)
{
return g_strdup(src);
}
static XsNode *xs_node_create(const char *name, GList *perms)
{
XsNode *n = xs_node_new();
#ifdef XS_NODE_UNIT_TEST
if (name) {
n->name = g_strdup(name);
}
#endif
n->perms = g_list_copy_deep(perms, do_perm_copy, NULL);
return n;
}
/* For copying from one hash table to another using g_hash_table_foreach() */
static void do_insert(gpointer key, gpointer value, gpointer user_data)
static void do_child_insert(gpointer key, gpointer value, gpointer user_data)
{
g_hash_table_insert(user_data, g_strdup(key), xs_node_ref(value));
}
@ -162,12 +211,16 @@ static XsNode *xs_node_copy(XsNode *old)
}
#endif
assert(old);
if (old->children) {
n->children = g_hash_table_new_full(g_str_hash, g_str_equal, g_free,
(GDestroyNotify)xs_node_unref);
g_hash_table_foreach(old->children, do_insert, n->children);
g_hash_table_foreach(old->children, do_child_insert, n->children);
}
if (old && old->content) {
if (old->perms) {
n->perms = g_list_copy_deep(old->perms, do_perm_copy, NULL);
}
if (old->content) {
n->content = g_byte_array_ref(old->content);
}
return n;
@ -383,6 +436,9 @@ static XsNode *xs_node_copy_deleted(XsNode *old, struct walk_op *op)
op->op_opaque2 = n->children;
g_hash_table_foreach(old->children, copy_deleted_recurse, op);
}
if (old->perms) {
n->perms = g_list_copy_deep(old->perms, do_perm_copy, NULL);
}
n->deleted_in_tx = true;
/* If it gets resurrected we only fire a watch if it lost its content */
if (old->content) {
@ -417,6 +473,104 @@ static int xs_node_rm(XsNode **n, struct walk_op *op)
return 0;
}
static int xs_node_get_perms(XsNode **n, struct walk_op *op)
{
GList **perms = op->op_opaque;
assert(op->inplace);
assert(*n);
*perms = g_list_copy_deep((*n)->perms, do_perm_copy, NULL);
return 0;
}
static void parse_perm(const char *perm, char *letter, unsigned int *dom_id)
{
unsigned int n = sscanf(perm, "%c%u", letter, dom_id);
assert(n == 2);
}
static bool can_access(unsigned int dom_id, GList *perms, const char *letters)
{
unsigned int i, n;
char perm_letter;
unsigned int perm_dom_id;
bool access;
if (dom_id == 0) {
return true;
}
n = g_list_length(perms);
assert(n >= 1);
/*
* The dom_id of the first perm is the owner, and the owner always has
* read-write access.
*/
parse_perm(g_list_nth_data(perms, 0), &perm_letter, &perm_dom_id);
if (dom_id == perm_dom_id) {
return true;
}
/*
* The letter of the first perm specified the default access for all other
* domains.
*/
access = !!strchr(letters, perm_letter);
for (i = 1; i < n; i++) {
parse_perm(g_list_nth_data(perms, i), &perm_letter, &perm_dom_id);
if (dom_id != perm_dom_id) {
continue;
}
access = !!strchr(letters, perm_letter);
}
return access;
}
static int xs_node_set_perms(XsNode **n, struct walk_op *op)
{
GList *perms = op->op_opaque;
if (op->dom_id) {
unsigned int perm_dom_id;
char perm_letter;
/* A guest may not change permissions on nodes it does not own */
if (!can_access(op->dom_id, (*n)->perms, "")) {
return EPERM;
}
/* A guest may not change the owner of a node it owns. */
parse_perm(perms->data, &perm_letter, &perm_dom_id);
if (perm_dom_id != op->dom_id) {
return EPERM;
}
if (g_list_length(perms) > XS_MAX_PERMS_PER_NODE) {
return ENOSPC;
}
}
/* We *are* the node to be written. Either this or a copy. */
if (!op->inplace) {
XsNode *old = *n;
*n = xs_node_copy(old);
xs_node_unref(old);
}
if ((*n)->perms) {
g_list_free_full((*n)->perms, g_free);
}
(*n)->perms = g_list_copy_deep(perms, do_perm_copy, NULL);
if (op->tx_id != XBT_NULL) {
(*n)->modified_in_tx = true;
}
return 0;
}
/*
* Passed a full reference in *n which it may free if it needs to COW.
*
@ -458,6 +612,13 @@ static int xs_node_walk(XsNode **n, struct walk_op *op)
}
if (!child_name) {
const char *letters = op->mutating ? "wb" : "rb";
if (!can_access(op->dom_id, old->perms, letters)) {
err = EACCES;
goto out;
}
/* This is the actual node on which the operation shall be performed */
err = op->op_fn(n, op);
if (!err) {
@ -491,12 +652,20 @@ static int xs_node_walk(XsNode **n, struct walk_op *op)
stole_child = true;
}
} else if (op->create_dirs) {
assert(op->mutating);
if (!can_access(op->dom_id, old->perms, "wb")) {
err = EACCES;
goto out;
}
if (op->dom_id && op->new_nr_nodes >= XS_MAX_DOMAIN_NODES) {
err = ENOSPC;
goto out;
}
child = xs_node_create(child_name, old->perms);
op->new_nr_nodes++;
child = xs_node_new();
/*
* If we're creating a new child, we can clearly modify it (and its
@ -918,20 +1087,73 @@ int xs_impl_rm(XenstoreImplState *s, unsigned int dom_id,
int xs_impl_get_perms(XenstoreImplState *s, unsigned int dom_id,
xs_transaction_t tx_id, const char *path, GList **perms)
{
/*
* The perms are (char *) in the <perm-as-string> wire format to be
* freed by the caller.
*/
return ENOSYS;
struct walk_op op;
XsNode **n;
int ret;
ret = init_walk_op(s, &op, tx_id, dom_id, path, &n);
if (ret) {
return ret;
}
op.op_fn = xs_node_get_perms;
op.op_opaque = perms;
return xs_node_walk(n, &op);
}
static void is_valid_perm(gpointer data, gpointer user_data)
{
char *perm = data;
bool *valid = user_data;
char letter;
unsigned int dom_id;
if (!*valid) {
return;
}
if (sscanf(perm, "%c%u", &letter, &dom_id) != 2) {
*valid = false;
return;
}
switch (letter) {
case 'n':
case 'r':
case 'w':
case 'b':
break;
default:
*valid = false;
break;
}
}
int xs_impl_set_perms(XenstoreImplState *s, unsigned int dom_id,
xs_transaction_t tx_id, const char *path, GList *perms)
{
/*
* The perms are (const char *) in the <perm-as-string> wire format.
*/
return ENOSYS;
struct walk_op op;
XsNode **n;
bool valid = true;
int ret;
if (!g_list_length(perms)) {
return EINVAL;
}
g_list_foreach(perms, is_valid_perm, &valid);
if (!valid) {
return EINVAL;
}
ret = init_walk_op(s, &op, tx_id, dom_id, path, &n);
if (ret) {
return ret;
}
op.op_fn = xs_node_set_perms;
op.op_opaque = perms;
op.mutating = true;
return xs_node_walk(n, &op);
}
int xs_impl_watch(XenstoreImplState *s, unsigned int dom_id, const char *path,
@ -1122,18 +1344,19 @@ static void xs_tx_free(void *_tx)
g_free(tx);
}
XenstoreImplState *xs_impl_create(void)
XenstoreImplState *xs_impl_create(unsigned int dom_id)
{
XenstoreImplState *s = g_new0(XenstoreImplState, 1);
GList *perms;
s->watches = g_hash_table_new_full(g_str_hash, g_str_equal, g_free, NULL);
s->transactions = g_hash_table_new_full(g_direct_hash, g_direct_equal,
NULL, xs_tx_free);
perms = g_list_append(NULL, xs_perm_as_string(XS_PERM_NONE, 0));
s->root = xs_node_create("/", perms);
g_list_free_full(perms, g_free);
s->nr_nodes = 1;
s->root = xs_node_new();
#ifdef XS_NODE_UNIT_TEST
s->root->name = g_strdup("/");
#endif
s->root_tx = s->last_tx = 1;
return s;

8
hw/i386/kvm/xenstore_impl.h
View file

@ -16,9 +16,15 @@ typedef uint32_t xs_transaction_t;
#define XBT_NULL 0
#define XS_PERM_NONE 0x00
#define XS_PERM_READ 0x01
#define XS_PERM_WRITE 0x02
typedef struct XenstoreImplState XenstoreImplState;
XenstoreImplState *xs_impl_create(void);
XenstoreImplState *xs_impl_create(unsigned int dom_id);
char *xs_perm_as_string(unsigned int perm, unsigned int domid);
/*
* These functions return *positive* error numbers. This is a little

27
tests/unit/test-xs-node.c
View file

@ -80,8 +80,9 @@ static void watch_cb(void *_str, const char *path, const char *token)
static XenstoreImplState *setup(void)
{
XenstoreImplState *s = xs_impl_create();
XenstoreImplState *s = xs_impl_create(DOMID_GUEST);
char *abspath;
GList *perms;
int err;
abspath = g_strdup_printf("/local/domain/%u", DOMID_GUEST);
@ -90,6 +91,13 @@ static XenstoreImplState *setup(void)
g_assert(!err);
g_assert(s->nr_nodes == 4);
perms = g_list_append(NULL, g_strdup_printf("n%u", DOMID_QEMU));
perms = g_list_append(perms, g_strdup_printf("r%u", DOMID_GUEST));
err = xs_impl_set_perms(s, DOMID_QEMU, XBT_NULL, abspath, perms);
g_assert(!err);
g_list_free_full(perms, g_free);
g_free(abspath);
abspath = g_strdup_printf("/local/domain/%u/some", DOMID_GUEST);
@ -98,6 +106,12 @@ static XenstoreImplState *setup(void)
g_assert(!err);
g_assert(s->nr_nodes == 5);
perms = g_list_append(NULL, g_strdup_printf("n%u", DOMID_GUEST));
err = xs_impl_set_perms(s, DOMID_QEMU, XBT_NULL, abspath, perms);
g_assert(!err);
g_list_free_full(perms, g_free);
g_free(abspath);
return s;
@ -166,6 +180,12 @@ static void test_xs_node_simple(void)
/* Keep a copy, to force COW mode */
old_root = xs_node_ref(s->root);
/* Write somewhere we aren't allowed, in COW mode */
err = write_str(s, DOMID_GUEST, XBT_NULL, "/local/domain/badplace",
"moredata");
g_assert(err == EACCES);
g_assert(s->nr_nodes == 7);
/* Write works again */
err = write_str(s, DOMID_GUEST, XBT_NULL,
"/local/domain/1/some/relative/path2",
@ -226,6 +246,11 @@ static void test_xs_node_simple(void)
g_assert(!err);
g_assert(s->nr_nodes == 8);
/* Write somewhere we aren't allowed */
err = write_str(s, DOMID_GUEST, XBT_NULL, "/local/domain/badplace",
"moredata");
g_assert(err == EACCES);
g_assert(!strcmp(guest_watches->str,
"/local/domain/1/some/relativewatchrel"));
g_string_truncate(guest_watches, 0);