linux-kernel - Re: [PATCH] relay: handle alloc_percpu returning NULL in relay

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Date:   Sat, 30 Nov 2019 17:04:45 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Cc:     akash.goel@...el.com, ajd@...ux.ibm.com,
        syzbot+1e925b4b836afe85a1c6@...kaller-ppc64.appspotmail.com,
        syzbot+587b2421926808309d21@...kaller-ppc64.appspotmail.com,
        syzbot+58320b7171734bf79d26@...kaller.appspotmail.com,
        syzbot+d6074fb08bdb2e010520@...kaller.appspotmail.com
Subject: Re: [PATCH] relay: handle alloc_percpu returning NULL in relay_open

Daniel Axtens <dja@...ens.net> writes:
> --
>
> There's a syz reproducer on the powerpc syzbot that eventually hits
> the bug, but it can take up to an hour or so before it keels over on a
> kernel with all the syzkaller debugging on, and even longer on a
> production kernel. I have been able to reproduce it once on a stock
> Ubuntu 5.0 ppc64le kernel.
>
> I will ask MITRE for a CVE - while only the process doing the syscall
> gets killed, it gets killed while holding the relay_channels_mutex,
> so it blocks all future relay activity.

CVE-2019-19462 has been assigned.

Regards,
Daniel


> ---
>  kernel/relay.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/relay.c b/kernel/relay.c
> index ade14fb7ce2e..a376cc6b54ec 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -580,7 +580,13 @@ struct rchan *relay_open(const char *base_filename,
>  	if (!chan)
>  		return NULL;
>  
> -	chan->buf = alloc_percpu(struct rchan_buf *);
> +	chan->buf = alloc_percpu_gfp(struct rchan_buf *,
> +				     GFP_KERNEL | __GFP_NOWARN);
> +	if (!chan->buf) {
> +		kfree(chan);
> +		return NULL;
> +	}
> +
>  	chan->version = RELAYFS_CHANNEL_VERSION;
>  	chan->n_subbufs = n_subbufs;
>  	chan->subbuf_size = subbuf_size;
> -- 
> 2.20.1