Fix nasty ncpfs symlink handling bug.

This bug could cause oopses and page state corruption, because ncpfs
used the generic page-cache symlink handlign functions.  But those
functions only work if the page cache is guaranteed to be "stable", ie a
page that was installed when the symlink walk was started has to still
be installed in the page cache at the end of the walk.

We could have fixed ncpfs to not use the generic helper routines, but it
is in many ways much cleaner to instead improve on the symlink walking
helper routines so that they don't require that absolute stability.

We do this by allowing "follow_link()" to return a error-pointer as a
cookie, which is fed back to the cleanup "put_link()" routine.  This
also simplifies NFS symlink handling.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 5 insertions, 5 deletions

diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
index 78af5850c558..1fd21f66f243 100644
--- a/fs/cifs/cifsfs.h
+++ b/fs/cifs/cifsfs.h
@@ -83,8 +83,8 @@ extern int cifs_dir_notify(struct file *, unsigned long arg);
 extern struct dentry_operations cifs_dentry_ops;
 
 /* Functions related to symlinks */
-extern int cifs_follow_link(struct dentry *direntry, struct nameidata *nd);
-extern void cifs_put_link(struct dentry *direntry, struct nameidata *nd);
+extern void *cifs_follow_link(struct dentry *direntry, struct nameidata *nd);
+extern void cifs_put_link(struct dentry *direntry, struct nameidata *nd, void *);
 extern int cifs_readlink(struct dentry *direntry, char __user *buffer, 
                          int buflen);
 extern int cifs_symlink(struct inode *inode, struct dentry *direntry,
diff --git a/fs/cifs/link.c b/fs/cifs/link.c
index bde0fabfece0..ab925ef4f863 100644
--- a/fs/cifs/link.c
+++ b/fs/cifs/link.c
@@ -92,7 +92,7 @@ cifs_hl_exit:
         return rc;
 }
 
-int
+void *
 cifs_follow_link(struct dentry *direntry, struct nameidata *nd)
 {
         struct inode *inode = direntry->d_inode;
@@ -148,7 +148,7 @@ out:
 out_no_free:
         FreeXid(xid);
         nd_set_link(nd, target_path);
-        return 0;
+        return NULL;    /* No cookie */
 }
 
 int
@@ -330,7 +330,7 @@ cifs_readlink(struct dentry *direntry, char __user *pBuffer, int buflen)
         return rc;
 }
 
-void cifs_put_link(struct dentry *direntry, struct nameidata *nd)
+void cifs_put_link(struct dentry *direntry, struct nameidata *nd, void *cookie)
 {
         char *p = nd_get_link(nd);
         if (!IS_ERR(p))