qga: Fix memory leak when output stream is unused

If capture-output is requested but one of the channels goes unused (eg.
we attempt to capture stderr but the command never writes to stderr), we
can leak memory.

guest_exec_output_watch() is (from what I understand) unconditionally
called for both streams if output capture is requested. The first call
will always pass the `p->size == p->length` check b/c both values are
0. Then GUEST_EXEC_IO_SIZE bytes will be allocated for the stream.

But when we reap the exited process there's a `gei->err.length > 0`
check to actually free the buffer. Which does not get run if the command
doesn't write to the stream.

Fix by making free() unconditional.

Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>

diff --git a/qga/commands.c b/qga/commands.c
index 09c683e263945dea7f1aa27a492f24ada521cf7c..ce172edd2d02dff6518a31a62b3a61a62900af45 100644 (file)
--- a/qga/commands.c
+++ b/qga/commands.c
@@ -206,15 +206,15 @@ GuestExecStatus *qmp_guest_exec_status(int64_t pid, Error **errp)
 #endif
         if (gei->out.length > 0) {
             ges->out_data = g_base64_encode(gei->out.data, gei->out.length);
-            g_free(gei->out.data);
             ges->has_out_truncated = gei->out.truncated;
         }
+        g_free(gei->out.data);
 
         if (gei->err.length > 0) {
             ges->err_data = g_base64_encode(gei->err.data, gei->err.length);
-            g_free(gei->err.data);
             ges->has_err_truncated = gei->err.truncated;
         }
+        g_free(gei->err.data);
 
         QTAILQ_REMOVE(&guest_exec_state.processes, gei, next);
         g_free(gei);