linux-kernel - Re: [PATCH 1/9] vfs: fix infinite loop caused by clone

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Message-Id: <E1P355b-0004SV-7f@pomaz-ex.szeredi.hu>
Date:	Tue, 05 Oct 2010 12:49:43 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...iv.linux.org.uk
CC:	dave@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] vfs: fix infinite loop caused by clone_mnt race

On Tue, 05 Oct 2010, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@...e.cz>
> 
> If clone_mnt() happens while mnt_make_readonly() is running, the
> cloned mount might have MNT_WRITE_HOLD flag set, which results in
> mnt_want_write() spinning forever on this mount.
> 
> Needs CAP_SYS_ADMIN to trigger deliberately and unlikely to happen
> accidentally.  But if it does happen it can hang the machine.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>

Forgot to add

CC: stable@...nel.org

> ---
>  fs/namespace.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/fs/namespace.c
> ===================================================================
> --- linux-2.6.orig/fs/namespace.c	2010-10-01 21:54:17.000000000 +0200
> +++ linux-2.6/fs/namespace.c	2010-10-01 21:54:30.000000000 +0200
> @@ -595,7 +595,7 @@ static struct vfsmount *clone_mnt(struct
>  				goto out_free;
>  		}
>  
> -		mnt->mnt_flags = old->mnt_flags;
> +		mnt->mnt_flags = old->mnt_flags & ~MNT_WRITE_HOLD;
>  		atomic_inc(&sb->s_active);
>  		mnt->mnt_sb = sb;
>  		mnt->mnt_root = dget(root);
> 
> -- 
> 
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