linux-ext4 - Re: [PATCH 11/13] fuse: fix UAF in rcu pathwalks

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Date: Wed, 6 Mar 2024 12:18:30 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: Christian Brauner <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, 
	linux-fsdevel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, 
	linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org, 
	linux-cifs@...r.kernel.org
Subject: Re: [PATCH 11/13] fuse: fix UAF in rcu pathwalks

On Tue, Mar 5, 2024 at 2:43 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Mon, 4 Mar 2024 at 15:36, Amir Goldstein <amir73il@...il.com> wrote:
>
> > Note that fuse_backing_files_free() calls
> > fuse_backing_id_free() => fuse_backing_free() => kfree_rcu()
> >
> > Should we move fuse_backing_files_free() into
> > fuse_conn_put() above fuse_dax_conn_free()?
> >
> > That will avoid the merge conflict and still be correct. no?
>
> Looks like a good cleanup.
>
> Force-pushed to fuse.git#for-next.
>

FYI, the version that you pushed will generate a minor conflict with

                }
-               fc->release(fc);
+               call_rcu(&fc->rcu, delayed_release);
        }
 }
 EXPORT_SYMBOL_GPL(fuse_conn_put);

If you move fuse_backing_files_free() to the start of the function,
I think merge conflict will be avoided:

 void fuse_conn_put(struct fuse_conn *fc)
 {
        if (refcount_dec_and_test(&fc->count)) {
                struct fuse_iqueue *fiq = &fc->iq;
                struct fuse_sync_bucket *bucket;

+               if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+                       fuse_backing_files_free(fc);
                if (IS_ENABLED(CONFIG_FUSE_DAX))
                        fuse_dax_conn_free(fc);


Thanks,
Amir.