MIME-Version: 1.0
References: <163967073889.1823006.12237147297060239168.stgit@warthog.procyon.org.uk>
 <163967172373.1823006.6118195970180365070.stgit@warthog.procyon.org.uk>
In-Reply-To: <163967172373.1823006.6118195970180365070.stgit@warthog.procyon.org.uk>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 16 Dec 2021 08:27:50 -0800
Message-ID: <CAHk-=wjiba2VRKKjOYAiCZn1Tk9H1tiXcOvjekdo3wPHHmedyQ@mail.gmail.com>
Subject: Re: [PATCH v3 57/68] afs: Fix afs_write_end() to handle len > page size
To:     David Howells <dhowells@redhat.com>
Cc:     linux-cachefs@redhat.com, Jeff Layton <jlayton@kernel.org>,
        Marc Dionne <marc.dionne@auristor.com>,
        Matthew Wilcox <willy@infradead.org>,
        linux-afs@lists.infradead.org,
        Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve French <sfrench@samba.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Omar Sandoval <osandov@osandov.com>,
        JeffleXu <jefflexu@linux.alibaba.com>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>,
        CIFS <linux-cifs@vger.kernel.org>, ceph-devel@vger.kernel.org,
        v9fs-developer@lists.sourceforge.net,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Dec 16, 2021 at 8:22 AM David Howells <dhowells@redhat.com> wrote:
>
> It is possible for the len argument to afs_write_end() to overrun the end
> of the page (len is used to key the size of the page in afs_write_start()
> when compound pages become a regular thing).

This smells like a bug in the caller.

It's just insane to call "write_end()" with a range that doesn't
actually fit in the page provided.

Exactly how does that happen, and why should AFS deal with it, not
whoever called write_end()?

              Linus