linux-kernel - Re: [PATCH 1/1] mm/madvise: replace ptrace attach requirement for process

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Date:   Mon, 11 Jan 2021 11:20:01 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, jannh@...gle.com, keescook@...omium.org,
        jeffv@...gle.com, minchan@...nel.org, mhocko@...e.com,
        shakeelb@...gle.com, rientjes@...gle.com, edgararriaga@...gle.com,
        timmurray@...gle.com, linux-mm@...ck.org, selinux@...r.kernel.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 1/1] mm/madvise: replace ptrace attach requirement for
 process_madvise

* Suren Baghdasaryan:

> diff --git a/mm/madvise.c b/mm/madvise.c
> index 6a660858784b..c2d600386902 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
>  		goto release_task;
>  	}
>  
> -	mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
> +	/* 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;
>  	}

Shouldn't this depend on the requested behavior?  Several operations
directly result in observable changes, and go beyond performance tuning.

Thanks,
Florian
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