linux-kernel - Re: [PATCH 1/2] mm/madvise: introduce PR_MADV_SELF flag to process

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Message-Id: <337e4359-37e0-4ed7-894d-6c88b3498a42@app.fastmail.com>
Date: Mon, 23 Sep 2024 21:49:43 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Lorenzo Stoakes" <lorenzo.stoakes@...cle.com>,
 "Shakeel Butt" <shakeel.butt@...ux.dev>
Cc: "Andrew Morton" <akpm@...ux-foundation.org>,
 "Vlastimil Babka" <vbabka@...e.cz>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 "Suren Baghdasaryan" <surenb@...gle.com>, linux-api@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 "Minchan Kim" <minchan@...nel.org>
Subject: Re: [PATCH 1/2] mm/madvise: introduce PR_MADV_SELF flag to process_madvise()

On Mon, Sep 23, 2024, at 19:34, Lorenzo Stoakes wrote:
> On Mon, Sep 23, 2024 at 11:56:06AM GMT, Shakeel Butt wrote:
>
> +	/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
> +	mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
> +	if (IS_ERR_OR_NULL(mm)) {
> +		ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
> +		goto release_task;
> +	}

Any chance we can fix mm_access() to not be able to return
a NULL pointer and an error pointer?  IS_ERR_OR_NULL() is
usually an indication of a confusing API, and this is
clearly one of them, given that only one of the
callers actually wants the NULL value instead of -ESRCH.

    Arnd