[Qemu-devel] [PATCH] monitor: fix use after free

[Michael S. Tsirkin]

The function monitor_fdset_dup_fd_find_remove() references member of
'mon_fdset' which - when remove flag is set - may be freed in function
monitor_fdset_cleanup().
remove is set by monitor_fdset_dup_fd_remove which in practice
does not need the returned value, so make it void,
and return -1 from monitor_fdset_dup_fd_find_remove.

Signed-off-by: Michael S. Tsirkin <address@hidden>
Reported-by: zhanghailiang <address@hidden>
---
 include/monitor/monitor.h | 2 +-
 monitor.c                 | 8 +++++---
 stubs/fdset-remove-fd.c   | 3 +--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
index 3d6929d..78a5fc8 100644
--- a/include/monitor/monitor.h
+++ b/include/monitor/monitor.h
@@ -64,7 +64,7 @@ AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, 
int64_t fdset_id,
                                 Error **errp);
 int monitor_fdset_get_fd(int64_t fdset_id, int flags);
 int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd);
-int monitor_fdset_dup_fd_remove(int dup_fd);
+void monitor_fdset_dup_fd_remove(int dup_fd);
 int monitor_fdset_dup_fd_find(int dup_fd);
 
 #endif /* !MONITOR_H */
diff --git a/monitor.c b/monitor.c
index cdbaa60..ba1908f 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2542,8 +2542,10 @@ static int monitor_fdset_dup_fd_find_remove(int dup_fd, 
bool remove)
                     if (QLIST_EMPTY(&mon_fdset->dup_fds)) {
                         monitor_fdset_cleanup(mon_fdset);
                     }
+                    return -1;
+                } else {
+                    return mon_fdset->id;
                 }
-                return mon_fdset->id;
             }
         }
     }
@@ -2555,9 +2557,9 @@ int monitor_fdset_dup_fd_find(int dup_fd)
     return monitor_fdset_dup_fd_find_remove(dup_fd, false);
 }
 
-int monitor_fdset_dup_fd_remove(int dup_fd)
+void monitor_fdset_dup_fd_remove(int dup_fd)
 {
-    return monitor_fdset_dup_fd_find_remove(dup_fd, true);
+    monitor_fdset_dup_fd_find_remove(dup_fd, true);
 }
 
 int monitor_handle_fd_param(Monitor *mon, const char *fdname)
diff --git a/stubs/fdset-remove-fd.c b/stubs/fdset-remove-fd.c
index b3886d9..7f6d61e 100644
--- a/stubs/fdset-remove-fd.c
+++ b/stubs/fdset-remove-fd.c
@@ -1,7 +1,6 @@
 #include "qemu-common.h"
 #include "monitor/monitor.h"
 
-int monitor_fdset_dup_fd_remove(int dupfd)
+void monitor_fdset_dup_fd_remove(int dupfd)
 {
-    return -1;
 }
-- 
MST