[PATCH] text backport of fix for tmpfs oops from 2.6.0 final to 2.4.23

[PATCH] text backport of fix for tmpfs oops from 2.6.0 final to 2.4.23

[James McMechan]

Stupid free mail program appears to have converted
my message into a octet stream, this should work
even if it is kind of strange. Travel without a good
connection is painful, Hopefully this is readable.

Ok, here is a backport of the patch that went into 2.6.0
to fix the problem where the tmpfs/shmfs dcache could be
oopsed by any user doing a dirseek to offset 2.
This occurs because the when the seek is at the cursor
and then the cursor is deleted, the list_add_tail
tries to attach to the end of the list and gets the
old pointers (poisoned on 2.6) from the list_del.
This fix just deletes the cursor before going over the
list since it can not be a member of the list and should
not be counted, delete it before counting over the list.

--- linux-2.4.23/fs/readdir.c 2002-08-02 17:39:45.000000000 -0700
+++ build-2.4.23-skas/fs/readdir.c 2003-12-23 17:18:37.000000000 -0800
@@ -69,6 +69,7 @@
    loff_t n = file->f_pos - 2;
 
    spin_lock(&dcache_lock);
+   list_del(&cursor->d_child);
    p = file->f_dentry->d_subdirs.next;
    while (n && p != &file->f_dentry->d_subdirs) {
     struct dentry *next;
@@ -77,7 +78,6 @@
      n--;
     p = p->next;
    }
-   list_del(&cursor->d_child);
    list_add_tail(&cursor->d_child, p);
    spin_unlock(&dcache_lock);
   }