From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 5/5] vfs: don't allow writes to swap files
Date: Wed, 26 Jun 2019 04:51:51 +0100
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To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: matthew.garrett@nebula.com, yuchao0@huawei.com, tytso@mit.edu, ard.biesheuvel@linaro.org, josef@toxicpanda.com, hch@infradead.org, clm@fb.com, adilger.kernel@dilger.ca, jack@suse.com, dsterba@suse.com, jaegeuk@kernel.org, jk@ozlabs.org, reiserfs-devel@vger.kernel.org, linux-efi@vger.kernel.org, devel@lists.orangefs.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-nilfs@vger.kernel.org, linux-mtd@lists.infradead.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org

On Tue, Jun 25, 2019 at 07:33:31PM -0700, Darrick J. Wong wrote:
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -236,6 +236,9 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de
>  	if (IS_IMMUTABLE(inode))
>  		return -EPERM;
>  
> +	if (IS_SWAPFILE(inode))
> +		return -ETXTBSY;
> +
>  	if ((ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) &&
>  	    IS_APPEND(inode))
>  		return -EPERM;

Er...  So why exactly is e.g. chmod(2) forbidden for swapfiles?  Or touch(1),
for that matter...

> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 596ac98051c5..1ca4ee8c2d60 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3165,6 +3165,19 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  	if (error)
>  		goto bad_swap;
>  
> +	/*
> +	 * Flush any pending IO and dirty mappings before we start using this
> +	 * swap file.
> +	 */
> +	if (S_ISREG(inode->i_mode)) {
> +		inode->i_flags |= S_SWAPFILE;
> +		error = inode_drain_writes(inode);
> +		if (error) {
> +			inode->i_flags &= ~S_SWAPFILE;
> +			goto bad_swap;
> +		}
> +	}

Why are swap partitions any less worthy of protection?