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Date: Thu, 20 Jun 2019 15:13:06 -0700 From: "Darrick J. Wong" <darrick.wong@...cle.com> To: "Theodore Ts'o" <tytso@....edu>, matthew.garrett@...ula.com, yuchao0@...wei.com, ard.biesheuvel@...aro.org, josef@...icpanda.com, clm@...com, adilger.kernel@...ger.ca, viro@...iv.linux.org.uk, jack@...e.com, 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, linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org, linux-mm@...ck.org, linux-nilfs@...r.kernel.org, linux-mtd@...ts.infradead.org, ocfs2-devel@....oracle.com, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org Subject: Re: [PATCH 1/6] mm/fs: don't allow writes to immutable files On Thu, Jun 20, 2019 at 05:52:12PM -0400, Theodore Ts'o wrote: > On Mon, Jun 10, 2019 at 09:46:17PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <darrick.wong@...cle.com> > > > > The chattr manpage has this to say about immutable files: > > > > "A file with the 'i' attribute cannot be modified: it cannot be deleted > > or renamed, no link can be created to this file, most of the file's > > metadata can not be modified, and the file can not be opened in write > > mode." > > > > Once the flag is set, it is enforced for quite a few file operations, > > such as fallocate, fpunch, fzero, rm, touch, open, etc. However, we > > don't check for immutability when doing a write(), a PROT_WRITE mmap(), > > a truncate(), or a write to a previously established mmap. > > > > If a program has an open write fd to a file that the administrator > > subsequently marks immutable, the program still can change the file > > contents. Weird! > > > > The ability to write to an immutable file does not follow the manpage > > promise that immutable files cannot be modified. Worse yet it's > > inconsistent with the behavior of other syscalls which don't allow > > modifications of immutable files. > > > > Therefore, add the necessary checks to make the write, mmap, and > > truncate behavior consistent with what the manpage says and consistent > > with other syscalls on filesystems which support IMMUTABLE. > > > > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com> > > I note that this patch doesn't allow writes to swap files. So Amir's > generic/554 test will still fail for those file systems that don't use > copy_file_range. I didn't add any IS_SWAPFILE checks here, so I'm not sure to what you're referring? > I'm indifferent as to whether you add a new patch, or include that > change in this patch, but perhaps we should fix this while we're > making changes in these code paths? The swapfile patches should be in a separate patch, which I was planning to work on but hadn't really gotten around to it. --D > - Ted
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