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Message-ID: <20190626035151.GA10613@ZenIV.linux.org.uk>
Date: Wed, 26 Jun 2019 04:51:51 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: matthew.garrett@...ula.com, yuchao0@...wei.com, tytso@....edu,
ard.biesheuvel@...aro.org, josef@...icpanda.com, hch@...radead.org,
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dsterba@...e.com, jaegeuk@...nel.org, jk@...abs.org,
reiserfs-devel@...r.kernel.org, linux-efi@...r.kernel.org,
devel@...ts.orangefs.org, linux-kernel@...r.kernel.org,
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linux-mm@...ck.org, linux-nilfs@...r.kernel.org,
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Subject: Re: [PATCH 5/5] vfs: don't allow writes to swap files
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?
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