qemu-ga: use key-value store to avoid recycling fd handles after restart
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 <mdroth@linux.vnet.ibm.com>
Cc: qemu-stable@nongnu.org
* fixed guest_file_handle_add() return value from uint64_t to int64_t
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 7a0202e..1c2aff3 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -129,14 +129,22 @@
QTAILQ_HEAD(, GuestFileHandle) filehandles;
} guest_file_state;
-static void guest_file_handle_add(FILE *fh)
+static int64_t guest_file_handle_add(FILE *fh, Error **errp)
{
GuestFileHandle *gfh;
+ int64_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 @@
{
FILE *fh;
int fd;
- int64_t ret = -1;
+ int64_t ret = -1, handle;
if (!has_mode) {
mode = "r";
@@ -184,9 +192,14 @@
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)
