migration/cpr: Fix coverity report in cpr_exec_persist_state()

Per reported and analyzed by Peter:

https://lore.kernel.org/r/CAFEAcA_mUQ2NeoguR5efrhw7XYGofnriWEA=+Dg+Ocvyam1wAw@mail.gmail.com

mfd leak is a false positive, try to use a coverity annotation (which I
didn't find manual myself, but still give it a shot).

Fix the other one by capture error if setenv() failed.  When at it, pass
the error to the top (cpr_state_save()).  Along the way, changing all
retval to bool when errp is around.

Resolves: Coverity CID 1641391
Resolves: Coverity CID 1641392
Fixes: efc6587313 ("migration: cpr-exec save and load")
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20251021220407.2662288-3-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

include/migration/cpr.h

@@ -41,7 +41,7 @@ MigMode cpr_get_incoming_mode(void);
 void cpr_set_incoming_mode(MigMode mode);
 bool cpr_is_incoming(void);
 
-int cpr_state_save(MigrationChannel *channel, Error **errp);
+bool cpr_state_save(MigrationChannel *channel, Error **errp);
 int cpr_state_load(MigrationChannel *channel, Error **errp);
 void cpr_state_close(void);
 struct QIOChannel *cpr_state_ioc(void);
@@ -56,7 +56,7 @@ QEMUFile *cpr_transfer_input(MigrationChannel *channel, Error **errp);
 void cpr_exec_init(void);
 QEMUFile *cpr_exec_output(Error **errp);
 QEMUFile *cpr_exec_input(Error **errp);
-void cpr_exec_persist_state(QEMUFile *f);
+bool cpr_exec_persist_state(QEMUFile *f, Error **errp);
 bool cpr_exec_has_state(void);
 void cpr_exec_unpersist_state(void);
 void cpr_exec_unpreserve_fds(void);

migration/cpr-exec.c

@@ -40,16 +40,22 @@ static QEMUFile *qemu_file_new_fd_output(int fd, const char *name)
     return qemu_file_new_output(ioc);
 }
 
-void cpr_exec_persist_state(QEMUFile *f)
+bool cpr_exec_persist_state(QEMUFile *f, Error **errp)
 {
     QIOChannelFile *fioc = QIO_CHANNEL_FILE(qemu_file_get_ioc(f));
+    /* coverity[leaked_storage] - mfd intentionally kept open across exec() */
     int mfd = dup(fioc->fd);
     char val[16];
 
     /* Remember mfd in environment for post-exec load */
     qemu_clear_cloexec(mfd);
     snprintf(val, sizeof(val), "%d", mfd);
-    g_setenv(CPR_EXEC_STATE_NAME, val, 1);
+    if (!g_setenv(CPR_EXEC_STATE_NAME, val, 1)) {
+        error_setg(errp, "Setting env %s = %s failed", CPR_EXEC_STATE_NAME, val);
+        return false;
+    }
+
+    return true;
 }
 
 static int cpr_exec_find_state(void)

migration/cpr.c

@@ -176,7 +176,7 @@ bool cpr_is_incoming(void)
     return incoming_mode != MIG_MODE_NONE;
 }
 
-int cpr_state_save(MigrationChannel *channel, Error **errp)
+bool cpr_state_save(MigrationChannel *channel, Error **errp)
 {
     int ret;
     QEMUFile *f;
@@ -190,10 +190,10 @@ int cpr_state_save(MigrationChannel *channel, Error **errp)
     } else if (mode == MIG_MODE_CPR_EXEC) {
         f = cpr_exec_output(errp);
     } else {
-        return 0;
+        return true;
     }
     if (!f) {
-        return -1;
+        return false;
     }
 
     qemu_put_be32(f, QEMU_CPR_FILE_MAGIC);
@@ -202,11 +202,14 @@ int cpr_state_save(MigrationChannel *channel, Error **errp)
     ret = vmstate_save_state(f, &vmstate_cpr_state, &cpr_state, 0, errp);
     if (ret) {
         qemu_fclose(f);
-        return ret;
+        return false;
     }
 
     if (migrate_mode() == MIG_MODE_CPR_EXEC) {
-        cpr_exec_persist_state(f);
+        if (!cpr_exec_persist_state(f, errp)) {
+            qemu_fclose(f);
+            return false;
+        }
     }
 
     /*
@@ -217,7 +220,7 @@ int cpr_state_save(MigrationChannel *channel, Error **errp)
     qio_channel_shutdown(qemu_file_get_ioc(f), QIO_CHANNEL_SHUTDOWN_WRITE,
                          NULL);
     cpr_state_file = f;
-    return 0;
+    return true;
 }
 
 int cpr_state_load(MigrationChannel *channel, Error **errp)

migration/migration.c

@@ -2301,7 +2301,7 @@ void qmp_migrate(const char *uri, bool has_channels,
         return;
     }
 
-    if (cpr_state_save(cpr_channel, &local_err)) {
+    if (!cpr_state_save(cpr_channel, &local_err)) {
         goto out;
     }