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Date:   Mon, 23 Nov 2020 10:47:19 -0500
From:   Tycho Andersen <tycho@tycho.pizza>
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
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Subject: Re: [PATCH v2 07/39] mount: attach mappings to mounts
Message-ID: <20201123154719.GD4025434@cisco>
References: <20201115103718.298186-1-christian.brauner@ubuntu.com>
 <20201115103718.298186-8-christian.brauner@ubuntu.com>
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In-Reply-To: <20201115103718.298186-8-christian.brauner@ubuntu.com>
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On Sun, Nov 15, 2020 at 11:36:46AM +0100, Christian Brauner wrote:
> +static inline struct user_namespace *mnt_user_ns(const struct vfsmount *mnt)
> +{
> +	return mnt->mnt_user_ns;
> +}

I think you might want a READ_ONCE() here. Right now it seems ok, since the
mnt_user_ns can't change, but if we ever allow it to change (and I see you have
a idmapped_mounts_wip_v2_allow_to_change_idmapping branch on your public tree
:D), the pattern of,

        user_ns = mnt_user_ns(path->mnt);
        if (mnt_idmapped(path->mnt)) {
                uid = kuid_from_mnt(user_ns, uid);
                gid = kgid_from_mnt(user_ns, gid);
        }

could race.

Tycho