netdev - Re: [PATCHv2] net: bpf: reject invalid shifts

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1452628118.1223.25.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 12 Jan 2016 11:48:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rabin Vincent <rabin@....in>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, ast@...nel.org,
	daniel@...earbox.net, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv2] net: bpf: reject invalid shifts

On Tue, 2016-01-12 at 20:17 +0100, Rabin Vincent wrote:
> On ARM64, a BUG() is triggered in the eBPF JIT if a filter with a
> constant shift that can't be encoded in the immediate field of the
> UBFM/SBFM instructions is passed to the JIT.  Since these shifts
> amounts, which are negative or >= regsize, are invalid, reject them in
> the eBPF verifier and the classic BPF filter checker, for all
> architectures.
> 

Hmm...

> diff --git a/net/core/filter.c b/net/core/filter.c
> index 672eefbfbe99..37157c4c1a78 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -777,6 +777,11 @@ static int bpf_check_classic(const struct sock_filter *filter,
>  			if (ftest->k == 0)
>  				return -EINVAL;
>  			break;
> +		case BPF_ALU | BPF_LSH | BPF_K:
> +		case BPF_ALU | BPF_RSH | BPF_K:
> +			if (ftest->k >= 32)
> +				return -EINVAL;
> +			break;
>  		case BPF_LD | BPF_MEM:
>  		case BPF_LDX | BPF_MEM:
>  		case BPF_ST:

These weak filters used to have undefined behavior, maybe in a never
taken branch, and will now fail hard, possibly breaking old
applications.

I believe we should add a one time warning to give a clue to poor users
hitting this problem.

Not everybody has perfect BPF filters, since most of the time they were
hand coded.