linux-kernel - Re: [PATCH 1/2] mm: add GFP mask param to strndup

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Message-ID: <20200815224210.GA1236603@ZenIV.linux.org.uk>
Date:   Sat, 15 Aug 2020 23:42:10 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Pascal Bouchareine <kalou@....net>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH 1/2] mm: add GFP mask param to strndup_user

On Sat, Aug 15, 2020 at 11:23:43AM -0700, Pascal Bouchareine wrote:
> Let caller specify allocation.
> Preserve existing calls with GFP_USER.

Bloody bad idea, unless you slap a BUG_ON(flags & GFP_ATOMIC) on it,
to make sure nobody tries _that_.  Note that copying from userland
is an inherently blocking operation, and this interface invites
just that.

What do you need that flag for, anyway?