netdev - Re: [PATCH] bpf: fix missing checks of the return value of check_reg

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Message-ID: <20181225072529.t53rszflr3apeexz@ast-mbp.dhcp.thefacebook.com>
Date:   Mon, 24 Dec 2018 23:25:31 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Kangjie Lu <kjlu@....edu>
Cc:     pakki001@....edu, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: fix missing checks of the return value of
 check_reg_arg

On Tue, Dec 25, 2018 at 01:17:10AM -0600, Kangjie Lu wrote:
> check_reg_arg() may fail. This fix inserts checks for its return value.
> If check_reg_arg() fails, issues an error message.
> 
> Signed-off-by: Kangjie Lu <kjlu@....edu>
> ---
>  kernel/bpf/verifier.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 51ba84d4d34a..fde91a5c0b5a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2619,7 +2619,10 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>  	/* after the call registers r0 - r5 were scratched */
>  	for (i = 0; i < CALLER_SAVED_REGS; i++) {
>  		mark_reg_not_init(env, caller->regs, caller_saved[i]);
> -		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
> +		err = check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
> +		if (err)
> +			verbose(env,
> +					"check_reg_arg() fails in setting caller saved regs\n");

Such patch was already posted.
These calls cannot fail.
I prefer to leave them as-is.