covscan: avoid false positive on g_clear_pointer()

This is a CLANG_WARNING found by covscan. It is a false positive as
g_clear_pointer() does set vportp to NULL, meaning that the situation
described by covscan below should not be reached. Moving away from
g_clear_pointer() in this specific case just to make our tool happy.

Covscan report:
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:458:9: warning: Use of memory after it is freed
 > #    if (wbuf->write_pos != wbuf->size) {
 > #        ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:268:12: note: Assuming the condition is true
 > #    while (*vportp && (*vportp)->write_buf)
 > #           ^~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:268:12: note: Left side of '&&' is true
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:268:5: note: Loop condition is true.  Entering loop body
 > #    while (*vportp && (*vportp)->write_buf)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:269:9: note: Calling 'vdagent_virtio_port_do_write'
 > #        vdagent_virtio_port_do_write(vportp);
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:453:5: note: Taking false branch
 > #    if (!wbuf) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:458:9: note: Assuming the condition is false
 > #    if (wbuf->write_pos != wbuf->size) {
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:458:5: note: Taking false branch
 > #    if (wbuf->write_pos != wbuf->size) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:465:9: note: Assuming 'n' is < 0
 > #    if (n < 0) {
 > #        ^~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:465:5: note: Taking true branch
 > #    if (n < 0) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:466:13: note: Assuming the condition is false
 > #        if (errno == EINTR)
 > #            ^~~~~~~~~~~~~~
 > /usr/include/errno.h:38:16: note: expanded from macro 'errno'
 > ## define errno (*__errno_location ())
 > #               ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:466:9: note: Taking false branch
 > #        if (errno == EINTR)
 > #        ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:469:9: note: Calling 'vdagent_virtio_port_destroy'
 > #        vdagent_virtio_port_destroy(vportp);
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:130:5: note: Taking false branch
 > #    if (!vport)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:133:9: note: Assuming the condition is false
 > #    if (vport->disconnect_callback)
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:133:5: note: Taking false branch
 > #    if (vport->disconnect_callback)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:137:5: note: Loop condition is true.  Entering loop body
 > #    while (wbuf) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:140:9: note: Memory is released
 > #        g_free(wbuf);
 > #        ^~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:137:5: note: Loop condition is false. Execution continues on line 144
 > #    while (wbuf) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:144:5: note: Loop condition is true.  Entering loop body
 > #    for (i = 0; i < VDP_END_PORT; i++) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:144:5: note: Loop condition is true.  Entering loop body
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:144:5: note: Loop condition is true.  Entering loop body
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:144:5: note: Loop condition is false. Execution continues on line 148
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:149:5: note: Assuming '_p' is null
 > #    g_clear_pointer(vportp, g_free);
 > #    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > /usr/include/glib-2.0/glib/gmem.h:124:9: note: expanded from macro 'g_clear_pointer'
 > #    if (_p)                                                                    \
 > #        ^~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:149:5: note: Taking false branch
 > /usr/include/glib-2.0/glib/gmem.h:124:5: note: expanded from macro 'g_clear_pointer'
 > #    if (_p)                                                                    \
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:149:5: note: Loop condition is false.  Exiting loop
 > /usr/include/glib-2.0/glib/gmem.h:114:3: note: expanded from macro 'g_clear_pointer'
 > #  G_STMT_START {                                                               \
 > #  ^
 > /usr/include/glib-2.0/glib/gmacros.h:346:23: note: expanded from macro 'G_STMT_START'
 > ##define G_STMT_START  do
 > #                      ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:469:9: note: Returning; memory was released
 > #        vdagent_virtio_port_destroy(vportp);
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:269:9: note: Returning; memory was released
 > #        vdagent_virtio_port_do_write(vportp);
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:268:12: note: Left side of '&&' is true
 > #    while (*vportp && (*vportp)->write_buf)
 > #           ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:268:5: note: Loop condition is true.  Entering loop body
 > #    while (*vportp && (*vportp)->write_buf)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:269:9: note: Calling 'vdagent_virtio_port_do_write'
 > #        vdagent_virtio_port_do_write(vportp);
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:453:5: note: Taking false branch
 > #    if (!wbuf) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagentd/virtio-port.c:458:9: note: Use of memory after it is freed
 > #    if (wbuf->write_pos != wbuf->size) {
 > #        ^~~~~~~~~~~~~~~
 > #  456|       }
 > #  457|
 > #  458|->     if (wbuf->write_pos != wbuf->size) {
 > #  459|           syslog(LOG_ERR, "do_write: buffer is incomplete!!");
 > #  460|           return;

Signed-off-by: Victor Toso <victortoso@redhat.com>
Acked-by: Frediano Ziglio <fziglio@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/vdagentd/virtio-port.c b/src/vdagentd/virtio-port.c
index b0556ce..3ae7f22 100644
--- a/src/vdagentd/virtio-port.c
+++ b/src/vdagentd/virtio-port.c
@@ -146,7 +146,8 @@ void vdagent_virtio_port_destroy(struct vdagent_virtio_port **vportp)
     }
 
     close(vport->fd);
-    g_clear_pointer(vportp, g_free);
+    g_free(vport);
+    *vportp = NULL;
 }
 
 int vdagent_virtio_port_fill_fds(struct vdagent_virtio_port *vport,