[gcab] trivial: Return earlier if nubytes is larger than CAB_BLOCKMAX

[Richard Hughes <rhughes src gnome org>]

commit 172a444132594a4803f75e601d0dd4576d4b3576
Author: Richard Hughes <richard hughsie com>
Date:   Mon Dec 18 12:25:17 2017 +0000

    trivial: Return earlier if nubytes is larger than CAB_BLOCKMAX
    
    There is no stack overwriting here, but it's a good idea to be paranoid.

 libgcab/cabinet.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/libgcab/cabinet.c b/libgcab/cabinet.c
index 82bf884..53d58bb 100644
--- a/libgcab/cabinet.c
+++ b/libgcab/cabinet.c
@@ -567,6 +567,13 @@ cdata_read (cdata_t *cd, guint8 res_data, gint comptype,
         return FALSE;
     }
     R2 (cd->nubytes);
+    if (cd->nubytes > CAB_BLOCKMAX) {
+        g_set_error (error, GCAB_ERROR, GCAB_ERROR_INVALID_DATA,
+                     "CDATA block of %" G_GUINT16_FORMAT " bytes "
+                     "was bigger than maximum size %i",
+                     cd->nubytes, CAB_BLOCKMAX);
+        return FALSE;
+    }
     RN (cd->reserved, res_data);
     RN (buf, cd->ncbytes);