linux-kernel - Re: [PATCH 1/3] ima: Remove inode lock

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Message-ID: <dg6qpjgqggq6lfehfosy6vtrhl6ddez3mg4vkpxgqoo2vytq4i@l4g6rx64ovcg>
Date: Fri, 18 Oct 2024 14:54:33 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Roberto Sassu <roberto.sassu@...weicloud.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Paul Moore <paul@...l-moore.com>, ebpqwerty472123@...il.com, kirill.shutemov@...ux.intel.com, 
	zohar@...ux.ibm.com, dmitry.kasatkin@...il.com, eric.snowberg@...cle.com, 
	jmorris@...ei.org, serge@...lyn.com, linux-integrity@...r.kernel.org, 
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Roberto Sassu <roberto.sassu@...wei.com>, linux-mm@...ck.org, akpm@...ux-foundation.org, vbabka@...e.cz, 
	linux-fsdevel@...r.kernel.org, Liam Howlett <liam.howlett@...cle.com>, 
	Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 1/3] ima: Remove inode lock

On Fri, Oct 18, 2024 at 01:22:35PM +0200, Roberto Sassu wrote:
> On Fri, 2024-10-18 at 14:05 +0300, Kirill A. Shutemov wrote:
> > On Fri, Oct 18, 2024 at 12:00:22PM +0100, Lorenzo Stoakes wrote:
> > > + Liam, Jann
> > > 
> > > On Fri, Oct 18, 2024 at 01:49:06PM +0300, Kirill A. Shutemov wrote:
> > > > On Fri, Oct 18, 2024 at 11:24:06AM +0200, Roberto Sassu wrote:
> > > > > Probably it is hard, @Kirill would there be any way to safely move
> > > > > security_mmap_file() out of the mmap_lock lock?
> > > > 
> > > > What about something like this (untested):
> > > > 
> > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > index dd4b35a25aeb..03473e77d356 100644
> > > > --- a/mm/mmap.c
> > > > +++ b/mm/mmap.c
> > > > @@ -1646,6 +1646,26 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> > > >  	if (pgoff + (size >> PAGE_SHIFT) < pgoff)
> > > >  		return ret;
> > > > 
> > > > +	if (mmap_read_lock_killable(mm))
> > > > +		return -EINTR;
> > > > +
> > > > +	vma = vma_lookup(mm, start);
> > > > +
> > > > +	if (!vma || !(vma->vm_flags & VM_SHARED)) {
> > > > +		mmap_read_unlock(mm);
> > > > +		return -EINVAL;
> > > > +	}
> > > > +
> > > > +	file = get_file(vma->vm_file);
> > > > +
> > > > +	mmap_read_unlock(mm);
> > > > +
> > > > +	ret = security_mmap_file(vma->vm_file, prot, flags);
> > > 
> > > Accessing VMA fields without any kind of lock is... very much not advised.
> > > 
> > > I'm guessing you meant to say:
> > > 
> > > 	ret = security_mmap_file(file, prot, flags);
> > > 
> > > Here? :)
> > 
> > Sure. My bad.
> > 
> > Patch with all fixups:
> 
> Thanks a lot! Let's wait a bit until the others have a chance to
> comment. Meanwhile, I will test it.
> 
> Do you want me to do the final patch, or will you be proposing it?

You can post it if it works:

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov