tests/virtio-9p: explicitly handle potential integer overflows

Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

tests/virtio-9p-test.c

@@ -168,7 +168,7 @@ static uint16_t v9fs_string_size(const char *string)
 {
     size_t len = strlen(string);
 
-    g_assert_cmpint(len, <=, UINT16_MAX);
+    g_assert_cmpint(len, <=, UINT16_MAX - 2);
 
     return 2 + len;
 }
@@ -209,17 +209,20 @@ static P9Req *v9fs_req_init(QVirtIO9P *v9p, uint32_t size, uint8_t id,
                             uint16_t tag)
 {
     P9Req *req = g_new0(P9Req, 1);
-    uint32_t t_size = 7 + size; /* 9P header has well-known size of 7 bytes */
+    uint32_t total_size = 7; /* 9P header has well-known size of 7 bytes */
     P9Hdr hdr = {
-        .size = cpu_to_le32(t_size),
         .id = id,
         .tag = cpu_to_le16(tag)
     };
 
-    g_assert_cmpint(t_size, <=, P9_MAX_SIZE);
+    g_assert_cmpint(total_size, <=, UINT32_MAX - size);
+    total_size += size;
+    hdr.size = cpu_to_le32(total_size);
+
+    g_assert_cmpint(total_size, <=, P9_MAX_SIZE);
 
     req->v9p = v9p;
-    req->t_size = t_size;
+    req->t_size = total_size;
     req->t_msg = guest_alloc(v9p->qs->alloc, req->t_size);
     v9fs_memwrite(req, &hdr, 7);
     req->tag = tag;
@@ -305,8 +308,13 @@ static void v9fs_rlerror(P9Req *req, uint32_t *err)
 static P9Req *v9fs_tversion(QVirtIO9P *v9p, uint32_t msize, const char *version,
                             uint16_t tag)
 {
-    P9Req *req = v9fs_req_init(v9p, 4 + v9fs_string_size(version), P9_TVERSION,
-                               tag);
+    P9Req *req;
+    uint32_t body_size = 4;
+    uint16_t string_size = v9fs_string_size(version);
+
+    g_assert_cmpint(body_size, <=, UINT32_MAX - string_size);
+    body_size += string_size;
+    req = v9fs_req_init(v9p, body_size, P9_TVERSION, tag);
 
     v9fs_uint32_write(req, msize);
     v9fs_string_write(req, version);
@@ -366,12 +374,15 @@ static P9Req *v9fs_twalk(QVirtIO9P *v9p, uint32_t fid, uint32_t newfid,
 {
     P9Req *req;
     int i;
-    uint32_t size = 4 + 4 + 2;
+    uint32_t body_size = 4 + 4 + 2;
 
     for (i = 0; i < nwname; i++) {
-        size += v9fs_string_size(wnames[i]);
+        uint16_t wname_size = v9fs_string_size(wnames[i]);
+
+        g_assert_cmpint(body_size, <=, UINT32_MAX - wname_size);
+        body_size += wname_size;
     }
-    req = v9fs_req_init(v9p,  size, P9_TWALK, tag);
+    req = v9fs_req_init(v9p,  body_size, P9_TWALK, tag);
     v9fs_uint32_write(req, fid);
     v9fs_uint32_write(req, newfid);
     v9fs_uint16_write(req, nwname);