The commit in the fixes line mistakenly modified the channels and
transport compatibility check logic so it now checks multi-channel
support only for socket transport type.

Thus, running multifd migration using a transport other than socket that
is incompatible with multi-channels (such as "exec") would lead to a
segmentation fault instead of an error message.
For example:
  (qemu) migrate_set_capability multifd on
  (qemu) migrate -d "exec:cat > /tmp/vm_state"
  Segmentation fault (core dumped)

Fix it by checking multi-channel compatibility for all transport types.

Fixes: d95533e1cdcc ("migration: modify migration_channels_and_uri_compatible() for new QAPI syntax")
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 migration/migration.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 219447dea1..6fc544711a 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -128,11 +128,17 @@ static bool migration_needs_multiple_sockets(void)
     return migrate_multifd() || migrate_postcopy_preempt();
 }
 
-static bool transport_supports_multi_channels(SocketAddress *saddr)
+static bool transport_supports_multi_channels(MigrationAddress *addr)
 {
-    return saddr->type == SOCKET_ADDRESS_TYPE_INET ||
-           saddr->type == SOCKET_ADDRESS_TYPE_UNIX ||
-           saddr->type == SOCKET_ADDRESS_TYPE_VSOCK;
+    if (addr->transport == MIGRATION_ADDRESS_TYPE_SOCKET) {
+        SocketAddress *saddr = &addr->u.socket;
+
+        return saddr->type == SOCKET_ADDRESS_TYPE_INET ||
+               saddr->type == SOCKET_ADDRESS_TYPE_UNIX ||
+               saddr->type == SOCKET_ADDRESS_TYPE_VSOCK;
+    }
+
+    return false;
 }
 
 static bool
@@ -140,8 +146,7 @@ migration_channels_and_transport_compatible(MigrationAddress *addr,
                                             Error **errp)
 {
     if (migration_needs_multiple_sockets() &&
-        (addr->transport == MIGRATION_ADDRESS_TYPE_SOCKET) &&
-        !transport_supports_multi_channels(&addr->u.socket)) {
+        !transport_supports_multi_channels(addr)) {
         error_setg(errp, "Migration requires multi-channel URIs (e.g. tcp)");
         return false;
     }
-- 
2.26.3

On Thu, Jan 25, 2024 at 06:25:12PM +0200, Avihai Horon wrote:
> The commit in the fixes line mistakenly modified the channels and
> transport compatibility check logic so it now checks multi-channel
> support only for socket transport type.
> 
> Thus, running multifd migration using a transport other than socket that
> is incompatible with multi-channels (such as "exec") would lead to a
> segmentation fault instead of an error message.
> For example:
>   (qemu) migrate_set_capability multifd on
>   (qemu) migrate -d "exec:cat > /tmp/vm_state"
>   Segmentation fault (core dumped)
> 
> Fix it by checking multi-channel compatibility for all transport types.
> 
> Fixes: d95533e1cdcc ("migration: modify migration_channels_and_uri_compatible() for new QAPI syntax")
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu