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

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Date:	Tue, 12 Jan 2016 10:51:22 -0800
From:	Alexei Starovoitov <alexei.starovoitov@...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: [PATCH] net: bpf: reject invalid shifts

On Tue, Jan 12, 2016 at 06:55:07PM +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 then in
> the eBPF verifier and the classic BPF filter checker, for all
> architectures.
> 
> Signed-off-by: Rabin Vincent <rabin@....in>
> ---
>  kernel/bpf/verifier.c | 10 ++++++++++
>  net/core/filter.c     |  5 +++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index a7945d10b378..3643df0dfaa9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1121,6 +1121,16 @@ static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn)
>  			return -EINVAL;
>  		}
>  
> +		if ((opcode == BPF_LSH || opcode == BPF_RSH) &&

Missing check for opcode == BPF_ARSH

Otherwise looks good. Thank you for fixing this!

> @@ -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:

here it's good. ARSH is eBPF only.