From: Dominique Martinet <asmadeus@codewreck.org>
To: Chengguang Xu <cgxu519@mykernel.net>
Cc: ericvh@gmail.com, lucho@ionkov.net,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
v9fs-developer@lists.sourceforge.net
Subject: Re: [V9fs-developer] [RFC PATCH] 9p: create writeback fid on shared mmap
Date: Sun, 6 Dec 2020 21:53:18 +0100 [thread overview]
Message-ID: <20201206205318.GA25257@nautica> (raw)
In-Reply-To: <20201206091618.GA22629@nautica>
Dominique Martinet wrote on Sun, Dec 06, 2020:
> Chengguang Xu wrote on Sat, Dec 05, 2020:
> > If vma is shared and the file was opened for writing,
> > we should also create writeback fid because vma may be
> > mprotected writable even if now readonly.
>
> Hm, I guess it makes sense.
I had a second look, and generic_file_readonly_mmap uses vma's
`vma->vm_flags & VM_MAYWRITE` instead (together with VM_SHARED),
while mapping_writably_mapped ultimately basically only seems to
validate that the mapping is shared from a look at mapping_map_writable
callers? It's not very clear to me.
OTOH, VM_MAYWRITE is set anytime we have a shared map where file has
been opened read-write, which seems to be what you want with regards to
protecting from mprotect calls.
How about simply changing check from WRITE to MAYWRITE?
v9inode = V9FS_I(inode);
mutex_lock(&v9inode->v_mutex);
if (!v9inode->writeback_fid &&
(vma->vm_flags & VM_SHARED) &&
- (vma->vm_flags & VM_WRITE)) {
+ (vma->vm_flags & VM_MAYWRITE)) {
/*
* clone a fid and add it to writeback_fid
* we do it during mmap instead of
--
Dominique
next prev parent reply other threads:[~2020-12-06 20:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-05 13:09 [RFC PATCH] 9p: create writeback fid on shared mmap Chengguang Xu
2020-12-06 9:16 ` Dominique Martinet
2020-12-06 20:53 ` Dominique Martinet [this message]
2020-12-07 6:02 ` [V9fs-developer] " Chengguang Xu
2020-12-07 11:24 ` Dominique Martinet
2020-12-07 13:13 ` Chengguang Xu
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