[Qemu-devel] [PATCH RFC v6 4/7] migration: fix some segmentation faults when using multifd

[Fei Li <fli@suse.com>]

When multifd is used during migration, a segmentaion fault will
occur in the source when multifd_save_cleanup() is called again if
the multifd_send_state has been freed in earlier error handling. This
can happen when migrate_fd_connect() fails and multifd_fd_cleanup()
is called, and then multifd_new_send_channel_async() fails and
multifd_save_cleanup() is called again.

If the QIOChannel *c of multifd_recv_state->params[i] (p->c) is not
initialized, there is no need to close the channel. Or else a
segmentation fault will occur in multifd_recv_terminate_threads()
when multifd_recv_initial_packet() fails.

Signed-off-by: Fei Li <fli@suse.com>
---
 migration/ram.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 7e7deec4d8..4db3b3e8f4 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -907,6 +907,11 @@ static void multifd_send_terminate_threads(Error *err)
         }
     }
 
+    /* in case multifd_send_state has been freed earlier */
+    if (!multifd_send_state) {
+        return;
+    }
+
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
 
@@ -922,7 +927,7 @@ int multifd_save_cleanup(Error **errp)
     int i;
     int ret = 0;
 
-    if (!migrate_use_multifd()) {
+    if (!migrate_use_multifd() || !multifd_send_state) {
         return 0;
     }
     multifd_send_terminate_threads(NULL);
@@ -960,7 +965,7 @@ static void multifd_send_sync_main(void)
 {
     int i;
 
-    if (!migrate_use_multifd()) {
+    if (!migrate_use_multifd() || !multifd_send_state) {
         return;
     }
     if (multifd_send_state->pages->used) {
@@ -1070,6 +1075,10 @@ static void multifd_new_send_channel_async(QIOTask *task, gpointer opaque)
     QIOChannel *sioc = QIO_CHANNEL(qio_task_get_source(task));
     Error *local_err = NULL;
 
+    if (!multifd_send_state) {
+        return;
+    }
+
     if (qio_task_propagate_error(task, &local_err)) {
         if (multifd_save_cleanup(&local_err) != 0) {
             migrate_set_error(migrate_get_current(), local_err);
@@ -1131,7 +1140,7 @@ struct {
     uint64_t packet_num;
 } *multifd_recv_state;
 
-static void multifd_recv_terminate_threads(Error *err)
+static void multifd_recv_terminate_threads(Error *err, bool channel)
 {
     int i;
 
@@ -1145,6 +1154,11 @@ static void multifd_recv_terminate_threads(Error *err)
         }
     }
 
+    /* in case p->c is not initialized */
+    if (!channel) {
+        return;
+    }
+
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
@@ -1166,7 +1180,7 @@ int multifd_load_cleanup(Error **errp)
     if (!migrate_use_multifd()) {
         return 0;
     }
-    multifd_recv_terminate_threads(NULL);
+    multifd_recv_terminate_threads(NULL, true);
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
@@ -1269,7 +1283,7 @@ static void *multifd_recv_thread(void *opaque)
     }
 
     if (local_err) {
-        multifd_recv_terminate_threads(local_err);
+        multifd_recv_terminate_threads(local_err, true);
     }
     qemu_mutex_lock(&p->mutex);
     p->running = false;
@@ -1331,7 +1345,7 @@ bool multifd_recv_new_channel(QIOChannel *ioc)
 
     id = multifd_recv_initial_packet(ioc, &local_err);
     if (id < 0) {
-        multifd_recv_terminate_threads(local_err);
+        multifd_recv_terminate_threads(local_err, false);
         return false;
     }
 
@@ -1339,7 +1353,7 @@ bool multifd_recv_new_channel(QIOChannel *ioc)
     if (p->c != NULL) {
         error_setg(&local_err, "multifd: received id '%d' already setup'",
                    id);
-        multifd_recv_terminate_threads(local_err);
+        multifd_recv_terminate_threads(local_err, true);
         return false;
     }
     p->c = ioc;
-- 
2.13.7