libafl_qemu: Returning errors in snapshots on saving and loading

[Tanmay140906]

Description

This PR propagates snapshot errors from QEMU to Rust by:

• Changing libafl_save_qemu_snapshot and libafl_load_qemu_snapshot to return int
• Returning -1 on failure and 0 on success
• Updating Rust bindings to return Result<(), QemuSnapshotError>
• Allowing users to handle snapshot failures explicitly

Async snapshot mode failure reports need to be handled yet.

Fixes #1512

Since the qemu_snapshot file and it's functions are generated during build time, these are the recommended changes to make so that this causes no code to break and works fine:

Changes

1. libafl/qemu_snapshot.c

-int libafl_save_qemu_snapshot(char* name, bool sync)
+int libafl_save_qemu_snapshot(char* name, bool sync)
 {
     ...
-        if (!save_snapshot(name, true, NULL, false, NULL, &err)) {
+        if (!save_snapshot(name, true, NULL, false, NULL, &err)) {
             error_report_err(err);
             error_report("Could not save snapshot");
-            return;
+            return -1;
         }
-        return;
+        return 0;
     }
     ...
-    return;
+    return 0;
 }

-int libafl_load_qemu_snapshot(char* name, bool sync)
+int libafl_load_qemu_snapshot(char* name, bool sync)
 {
     ...
-        if (!loaded) {
+        if (!loaded) {
             error_report_err(err);
             error_report("Could not load snapshot");
-            return;
+            return -1;
         }
         ...
-        return;
+        return 0;
     }
     ...
-    return;
+    return 0;
 }

2. libafl/qemu_snapshot.h

-void libafl_save_qemu_snapshot(char* name, bool sync);
-void libafl_load_qemu_snapshot(char* name, bool sync);
+int libafl_save_qemu_snapshot(char* name, bool sync);
+int libafl_load_qemu_snapshot(char* name, bool sync);

Checklist

• I have run ./scripts/precommit.sh and addressed all comments