linux-kernel - Re: [PATCH next V3] proc: support file->f_pos checking in mem

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Date:   Fri, 10 Nov 2023 08:21:11 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Zizhi Wo <wozizhi@...wei.com>
Cc:     brauner@...nel.org, akpm@...ux-foundation.org, oleg@...hat.com,
        jlayton@...nel.org, dchinner@...hat.com, adobriyan@...il.com,
        yang.lee@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, yangerkun@...wei.com
Subject: Re: [PATCH next V3] proc: support file->f_pos checking in mem_lseek

On Fri, Nov 10, 2023 at 11:19:28PM +0800, Zizhi Wo wrote:
> From: WoZ1zh1 <wozizhi@...wei.com>
> 
> In mem_lseek, file->f_pos may overflow. And it's not a problem that
> mem_open set file mode with FMODE_UNSIGNED_OFFSET(memory_lseek). However,
> another file use mem_lseek do lseek can have not FMODE_UNSIGNED_OFFSET
> (kpageflags_proc_ops/proc_pagemap_operations...), so in order to prevent
> file->f_pos updated to an abnormal number, fix it by checking overflow and
> FMODE_UNSIGNED_OFFSET.

1) How is that different from the previous version?
2) Would FMODE_UNSIGNED_OFFSET be wrong for those files?  If not, why not?