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Date:   Sun, 9 Jun 2019 21:41:44 -0700
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     "Theodore Ts'o" <tytso@mit.edu>
Cc:     linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 1/8] mm/fs: don't allow writes to immutable files
Message-ID: <20190610044144.GA1872750@magnolia>
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 <155552787330.20411.11893581890744963309.stgit@magnolia>
 <20190610015145.GB3266@mit.edu>
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On Sun, Jun 09, 2019 at 09:51:45PM -0400, Theodore Ts'o wrote:
> On Wed, Apr 17, 2019 at 12:04:33PM -0700, Darrick J. Wong wrote:
> > diff --git a/mm/memory.c b/mm/memory.c
> > index ab650c21bccd..dfd5eba278d6 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -2149,6 +2149,9 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
> >  
> >  	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
> >  
> > +	if (vmf->vma->vm_file && IS_IMMUTABLE(file_inode(vmf->vma->vm_file)))
> > +		return VM_FAULT_SIGBUS;
> > +
> >  	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
> >  	/* Restore original flags so that caller is not surprised */
> >  	vmf->flags = old_flags;
> 
> Shouldn't this check be moved before the modification of vmf->flags?
> It looks like do_page_mkwrite() isn't supposed to be returning with
> vmf->flags modified, lest "the caller gets surprised".

Yeah, I think that was a merge error during a rebase... :(

Er ... if you're still planning to take this patch through your tree,
can you move it to above the "vmf->flags = FAULT_FLAG_WRITE..." ?

--D

> 	   	     	       	      	   - Ted