util/grub-editenv: Fix incorrect casting of a signed value

The return value of ftell() may be negative (-1) on error. While it is
probably unlikely to occur, we should not blindly cast to an unsigned
value without first testing that it is not negative.

Fixes: CID 73856
Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/util/grub-editenv.c b/util/grub-editenv.c
index f3662c95ba66c25662a6827dbfd8bc468c1d07b4..db6f187cc63a9cea59546bb02b4266e3bfc51389 100644 (file)
--- a/util/grub-editenv.c
+++ b/util/grub-editenv.c
@@ -125,6 +125,7 @@ open_envblk_file (const char *name)
 {
   FILE *fp;
   char *buf;
+  long loc;
   size_t size;
   grub_envblk_t envblk;
 
@@ -143,7 +144,12 @@ open_envblk_file (const char *name)
     grub_util_error (_("cannot seek `%s': %s"), name,
                     strerror (errno));
 
-  size = (size_t) ftell (fp);
+  loc = ftell (fp);
+  if (loc < 0)
+    grub_util_error (_("cannot get file location `%s': %s"), name,
+                    strerror (errno));
+
+  size = (size_t) loc;
 
   if (fseek (fp, 0, SEEK_SET) < 0)
     grub_util_error (_("cannot seek `%s': %s"), name,