linux-kernel - Re: [PATCH v3 57/68] afs: Fix afs_write

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Date:   Thu, 16 Dec 2021 08:27:50 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, Jeff Layton <jlayton@...nel.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-afs@...ts.infradead.org,
        Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        JeffleXu <jefflexu@...ux.alibaba.com>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@...r.kernel.org>,
        CIFS <linux-cifs@...r.kernel.org>, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 57/68] afs: Fix afs_write_end() to handle len > page size

On Thu, Dec 16, 2021 at 8:22 AM David Howells <dhowells@...hat.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