Bug#254475: The bug is still there in 0.97-21

[Friedemann Baitinger]

have spent some time debugging the problem. I believe I have found two bugs:

The file /boot/grub/default was opened in read-only mode:

fopen(file, "r");

Later we're trying to write to it. In addition, the function
"read(&line, -1)" doesn't seem to do what it is supposed to do. "line" 
always has garbage afterwards", needless to say that the two values we 
later want to sscanf() out if it never get a value assigned so they stay 
at the static initialized values of "-1". I don't know where 
"read(&line, -1)" really reads from and where its prototype is declared 
nor what library implements it but it definitely doesn't do what it is 
supposed to do.

Here is a patch that I have verified that it really works:

--- builtins.c.orig     2007-01-28 16:46:18.000000000 +0100
+++ builtins.c  2007-01-28 18:33:17.000000000 +0100
@@ -3574,16 +3574,16 @@
    default_file[i] = 0;
    grub_strncat (default_file + i, "default", DEFAULT_FILE_BUFLEN - i);

-  if(!(fp = fopen(default_file,"w")))
+  if(!(fp = fopen(default_file,"r+")))
      {
        errnum = ERR_READ;
        goto fail;
      }

-  read(&line, -1);
-
+  fgets(line, bytes, fp);
+
    sscanf(line, "%d:%d", &curr_prev_default, &curr_default);
-
+
    if(curr_default != -1)
      new_prev_default = curr_default;
    else
@@ -3599,6 +3599,7 @@
    else
      sprintf(buf, "%d\n", new_default);

+  rewind(fp);
    fprintf(fp, buf);

  fail:


-- 
Friedemann Baitinger   baiti at web.de