Re: 2.6.7-rc2: open() hangs on ReiserFS with SELinux enabled

[Stephen Smalley]

On Thu, 2004-06-03 at 10:09, Stephen Smalley wrote:
> Ok, so vfs_create calls security_inode_post_create hook, and SELinux
> attempts to set the xattr on the newly created inode.  But reiserfs
> xattr implementation attempts to create a directory to store the xattr,
> and the attempt to instantiate the dentry for the directory inode causes
> the security_d_instantiate hook to be called, so that SELinux then
> attempts to get the xattr value for that directory inode to initialize
> the directory inode's security field before it becomes accessible via
> the dcache.  More generally, reiserfs_mkdir code is calling
> d_instantiate while holding reiserfs_write_lock, but d_instantiate can
> _block_ under SELinux due to need to fetch xattr for inode.  See
> http://marc.theaimsgroup.com/?l=linux-kernel&m=106712276514199&w=2 for
> related discussion.

Actually, that last part may be a red herring, since reiserfs_write_lock
is simply a macro for lock_kernel.  The more immediate concern is
avoiding the inode->i_op->getxattr call from SELinux on the xattr
directory inode.  reiserfs xattr code would need to call a new security
hook to mark the xattr root directory inode in some manner, so that
subsequent security_d_instantiate calls on the per-object subdirectories
could be identified by SELinux, and it could then just set the SID on
the incore inode to a well-defined value and not call
inode->i_op->getxattr for those inodes.

-- 
Stephen Smalley <sds@xxxxxxxxxxxxxx>
National Security Agency

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