linux-kernel - Re: [RFC PATCH 2/2] NFS: Fix a potential deadlock in nfs_file

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 9 Jan 2010 01:54:19 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] NFS: Fix a potential deadlock in
	nfs_file_mmap()

On Fri, Jan 08, 2010 at 07:56:24PM -0500, Trond Myklebust wrote:
> We cannot call nfs_invalidate_mapping() inside file->f_ops->mmap(), since
> this would cause us to grab the inode->i_mutex while already holding the
> current->mm->mmap_sem (thus causing a potential ABBA deadlock with the file
> write code, which can grab those locks in the opposite order).
> 
> We can fix this situation for the mmap() system call by using the new
> mmap_pgoff() callback, which is called prior to taking the
> current->mm->mmap_sem mutex.
> 
> We also add ensure that open() invalidates the mapping if the inode data is
> stale so that other users of mmap() (mainly the exec and uselib system
> calls) get up to date data too.
 
> +	status = nfs_revalidate_mapping(inode, file->f_mapping);
> +	if (status < 0)
> +		return status;
> +
> +	return generic_file_mmap_pgoff(file, addr, len, prot, flags, pgoff);

This is completely bogus.  Why do you need i_mutex for that and what
the <expletives> does that really prevent?  You might wait for a _loong_
time waiting for that mmap_sem, so what is really going on there?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/