wasmtime: harden wasm_interpret_header func

Signed-off-by: Maximilian Hüter <t4chib4ne@mailbox.org>

Author: t4chib4ne

src/libcrun/handlers/handler-utils.c

@@ -72,11 +72,14 @@ wasm_can_handle_container (libcrun_container_t *container, libcrun_error_t *err
 }
 
 wasm_encoding_t
-wasm_interpete_header (const char *header)
+wasm_interpret_header (const char *header, const size_t len)
 {
+  if (len < 8)
+    return WASM_ENC_INVALID;
+
   // Check for the WebAssembly magic bytes
   // See: https://webassembly.github.io/spec/core/binary/modules.html#binary-module
-  if (strncmp (header, "\0asm", 4))
+  if (memcmp (header, "\0asm", 4))
     return WASM_ENC_INVALID;
 
   /* The next four bytes are the WebAssembly version.

src/libcrun/handlers/handler-utils.h

@@ -30,6 +30,6 @@ typedef enum
 
 int wasm_can_handle_container (libcrun_container_t *container, libcrun_error_t *err);
 
-wasm_encoding_t wasm_interpete_header (const char *header);
+wasm_encoding_t wasm_interpret_header (const char *header, const size_t len);
 
 #endif

src/libcrun/handlers/wasmtime.c

@@ -117,7 +117,7 @@ libwasmtime_exec (void *cookie, libcrun_container_t *container arg_unused,
       wasm = wasm_bytes;
     }
 
-  wasm_encoding_t wasm_enc = wasm_interpete_header (wasm.data);
+  wasm_encoding_t wasm_enc = wasm_interpret_header (wasm.data, wasm.size);
   if (wasm_enc == WASM_ENC_INVALID)
     error (EXIT_FAILURE, 0, "invalid wasm binary header");