Hosts hold on to handles provided by guest-file-open for periods that can
span beyond the life of the qemu-ga process that issued them. Since these
are issued starting from 0 on every restart, we run the risk of issuing
duplicate handles after restarts/reboots.
As a result, users with a stale copy of these handles may end up
reading/writing corrupted data due to their existing handles effectively
being re-assigned to an unexpected file or offset.
We unfortunately do not issue handles as strings, but as integers, so a
solution such as using UUIDs can't be implemented without introducing a
new interface.
As a workaround, we fix this by implementing a persistent key-value store
that will be used to track the value of the last handle that was issued
across restarts/reboots to avoid issuing duplicates.
The store is automatically written to the same directory we currently
set via --statedir to track fsfreeze state, and so should be applicable
for stable releases where this flag is supported.
A follow-up can use this same store for handling fsfreeze state, but
that change is cosmetic and left out for now.
Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com>
Cc: qemu-sta...@nongnu.org
---
qga/commands-posix.c | 25 +++++--
qga/guest-agent-core.h | 1 +
qga/main.c | 184 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 204 insertions(+), 6 deletions(-)
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 7a0202e..5d12716 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -129,14 +129,22 @@ static struct {
QTAILQ_HEAD(, GuestFileHandle) filehandles;
} guest_file_state;
-static void guest_file_handle_add(FILE *fh)
+static uint64_t guest_file_handle_add(FILE *fh, Error **errp)
{
GuestFileHandle *gfh;
+ uint64_t handle;
+
+ handle = ga_get_fd_handle(ga_state, errp);
+ if (error_is_set(errp)) {
+ return 0;
+ }
gfh = g_malloc0(sizeof(GuestFileHandle));
- gfh->id = fileno(fh);
+ gfh->id = handle;
gfh->fh = fh;
QTAILQ_INSERT_TAIL(&guest_file_state.filehandles, gfh, next);
+
+ return handle;
}
static GuestFileHandle *guest_file_handle_find(int64_t id, Error **err)
@@ -158,7 +166,7 @@ int64_t qmp_guest_file_open(const char *path, bool
has_mode, const char *mode, E
{
FILE *fh;
int fd;
- int64_t ret = -1;
+ int64_t ret = -1, handle;
if (!has_mode) {
mode = "r";
@@ -184,9 +192,14 @@ int64_t qmp_guest_file_open(const char *path, bool
has_mode, const char *mode, E
return -1;
}
- guest_file_handle_add(fh);
- slog("guest-file-open, handle: %d", fd);
- return fd;
+ handle = guest_file_handle_add(fh, err);
+ if (error_is_set(err)) {
+ fclose(fh);
+ return -1;
+ }
+
+ slog("guest-file-open, handle: %d", handle);
+ return handle;
}
void qmp_guest_file_close(int64_t handle, Error **err)
diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h
index 3354598..624a559 100644
--- a/qga/guest-agent-core.h
+++ b/qga/guest-agent-core.h
@@ -35,6 +35,7 @@ bool ga_is_frozen(GAState *s);
void ga_set_frozen(GAState *s);
void ga_unset_frozen(GAState *s);
const char *ga_fsfreeze_hook(GAState *s);
+int64_t ga_get_fd_handle(GAState *s, Error **errp);
#ifndef _WIN32
void reopen_fd_to_null(int fd);
diff --git a/qga/main.c b/qga/main.c
index db281a5..3635430 100644
--- a/qga/main.c
+++ b/qga/main.c
@@ -15,6 +15,7 @@
#include <stdbool.h>
#include <glib.h>
#include <getopt.h>
+#include <glib/gstdio.h>
#ifndef _WIN32
#include <syslog.h>
#include <sys/wait.h>
@@ -30,6 +31,7 @@
#include "qapi/qmp/qerror.h"
#include "qapi/qmp/dispatch.h"
#include "qga/channel.h"
+#include "qemu/bswap.h"
#ifdef _WIN32
#include "qga/service-win32.h"
#include <windows.h>
@@ -53,6 +55,11 @@
#endif
#define QGA_SENTINEL_BYTE 0xFF
+typedef struct GAPersistentState {
+#define QGA_PSTATE_DEFAULT_FD_COUNTER 1000
+ int64_t fd_counter;
+} GAPersistentState;
+
struct GAState {
JSONMessageParser parser;
GMainLoop *main_loop;
@@ -76,6 +83,8 @@ struct GAState {
#ifdef CONFIG_FSFREEZE
const char *fsfreeze_hook;
#endif
+ const gchar *pstate_filepath;
+ GAPersistentState pstate;
};
struct GAState *ga_state;
@@ -724,6 +733,171 @@ VOID WINAPI service_main(DWORD argc, TCHAR *argv[])
}
#endif
+static void set_persistent_state_defaults(GAPersistentState *pstate)
+{
+ g_assert(pstate);
+ pstate->fd_counter = QGA_PSTATE_DEFAULT_FD_COUNTER;
+}
+
+static void persistent_state_from_keyfile(GAPersistentState *pstate,
+ GKeyFile *keyfile)
+{
+ g_assert(pstate);
+ g_assert(keyfile);
+ /* if any fields are missing, either because the file was tampered with
+ * by agents of chaos, or because the field wasn't present at the time the
+ * file was created, the best we can ever do is start over with the default
+ * values. so load them now, and ignore any errors in accessing key-value
+ * pairs
+ */
+ set_persistent_state_defaults(pstate);
+
+ if (g_key_file_has_key(keyfile, "global", "fd_counter", NULL)) {
+ pstate->fd_counter =
+ g_key_file_get_int64(keyfile, "global", "fd_counter", NULL);
+ }
+}
+
+static void persistent_state_to_keyfile(const GAPersistentState *pstate,
+ GKeyFile *keyfile)
+{
+ g_assert(pstate);
+ g_assert(keyfile);
+
+ g_key_file_set_int64(keyfile, "global", "fd_counter", pstate->fd_counter);
+}
+
+static gboolean write_persistent_state(const GAPersistentState *pstate,
+ const gchar *path)
+{
+ GKeyFile *keyfile = g_key_file_new();
+ GError *gerr = NULL;
+ gboolean ret = true;
+ gchar *data = NULL;
+ gsize data_len;
+
+ g_assert(pstate);
+
+ persistent_state_to_keyfile(pstate, keyfile);
+ data = g_key_file_to_data(keyfile, &data_len, &gerr);
+ if (gerr) {
+ g_critical("failed to convert persistent state to string: %s",
+ gerr->message);
+ ret = false;
+ goto out;
+ }
+
+ g_file_set_contents(path, data, data_len, &gerr);
+ if (gerr) {
+ g_critical("failed to write persistent state to %s: %s",
+ path, gerr->message);
+ ret = false;
+ goto out;
+ }
+
+out:
+ if (gerr) {
+ g_error_free(gerr);
+ }
+ if (keyfile) {
+ g_key_file_free(keyfile);
+ }
+ g_free(data);
+ return ret;
+}
+
+static gboolean read_persistent_state(GAPersistentState *pstate,
+ const gchar *path, gboolean frozen)
+{
+ GKeyFile *keyfile = NULL;
+ GError *gerr = NULL;
+ struct stat st;
+ gboolean ret = true;
+
+ g_assert(pstate);
+
+ if (stat(path, &st) == -1) {
+ /* it's okay if state file doesn't exist, but any other error
+ * indicates a permissions issue or some other misconfiguration
+ * that we likely won't be able to recover from.
+ */
+ if (errno != ENOENT) {
+ g_critical("unable to access state file at path %s: %s",
+ path, strerror(errno));
+ ret = false;
+ goto out;
+ }
+
+ /* file doesn't exist. initialize state to default values and
+ * attempt to save now. (we could wait till later when we have
+ * modified state we need to commit, but if there's a problem,
+ * such as a missing parent directory, we want to catch it now)
+ *
+ * there is a potential scenario where someone either managed to
+ * update the agent from a version that didn't use a key store
+ * while qemu-ga thought the filesystem was frozen, or
+ * deleted the key store prior to issuing a fsfreeze, prior
+ * to restarting the agent. in this case we go ahead and defer
+ * initial creation till we actually have modified state to
+ * write, otherwise fail to recover from freeze.
+ */
+ set_persistent_state_defaults(pstate);
+ if (!frozen) {
+ ret = write_persistent_state(pstate, path);
+ if (!ret) {
+ g_critical("unable to create state file at path %s", path);
+ ret = false;
+ goto out;
+ }
+ }
+ ret = true;
+ goto out;
+ }
+
+ keyfile = g_key_file_new();
+ g_key_file_load_from_file(keyfile, path, 0, &gerr);
+ if (gerr) {
+ g_critical("error loading persistent state from path: %s, %s",
+ path, gerr->message);
+ ret = false;
+ goto out;
+ }
+
+ persistent_state_from_keyfile(pstate, keyfile);
+
+out:
+ if (keyfile) {
+ g_key_file_free(keyfile);
+ }
+ if (gerr) {
+ g_error_free(gerr);
+ }
+
+ return ret;
+}
+
+int64_t ga_get_fd_handle(GAState *s, Error **errp)
+{
+ int64_t handle;
+
+ g_assert(s->pstate_filepath);
+ /* we blacklist commands and avoid operations that potentially require
+ * writing to disk when we're in a frozen state. this includes opening
+ * new files, so we should never get here in that situation
+ */
+ g_assert(!ga_is_frozen(s));
+
+ handle = s->pstate.fd_counter++;
+ if (s->pstate.fd_counter < 0) {
+ s->pstate.fd_counter = 0;
+ }
+ if (!write_persistent_state(&s->pstate, s->pstate_filepath)) {
+ error_setg(errp, "failed to commit persistent state to disk");
+ }
+
+ return handle;
+}
+
int main(int argc, char **argv)
{
const char *sopt = "hVvdm:p:l:f:F::b:s:t:";
@@ -853,7 +1027,9 @@ int main(int argc, char **argv)
ga_enable_logging(s);
s->state_filepath_isfrozen = g_strdup_printf("%s/qga.state.isfrozen",
state_dir);
+ s->pstate_filepath = g_strdup_printf("%s/qga.state", state_dir);
s->frozen = false;
+
#ifndef _WIN32
/* check if a previous instance of qemu-ga exited with filesystems' state
* marked as frozen. this could be a stale value (a non-qemu-ga process
@@ -910,6 +1086,14 @@ int main(int argc, char **argv)
}
}
+ /* load persistent state from disk */
+ if (!read_persistent_state(&s->pstate,
+ s->pstate_filepath,
+ ga_is_frozen(s))) {
+ g_critical("failed to load persistent state");
+ goto out_bad;
+ }
+
if (blacklist) {
s->blacklist = blacklist;
do {
--
1.7.9.5
