netdev - Re: [PATCH net] bpf: uninitialized variables in test code

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Date:   Sat, 1 Dec 2018 11:28:46 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Roman Gushchin <guro@...com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH net] bpf: uninitialized variables in test code

On Sat, Dec 01, 2018 at 07:13:50PM +0000, Roman Gushchin wrote:
> On Fri, Nov 30, 2018 at 02:58:03PM -0800, Alexei Starovoitov wrote:
> > On Thu, Nov 29, 2018 at 01:27:03PM +0300, Dan Carpenter wrote:
> > > Smatch complains that if bpf_test_run() fails with -ENOMEM at the
> > > begining then the "duration" is uninitialized.  We then copy the
> > > unintialized variables to the user inside the bpf_test_finish()
> > > function.  The functions require CAP_SYS_ADMIN so it's not really an
> > > information leak.
> > > 
> > > Fixes: 1cf1cae963c2 ("bpf: introduce BPF_PROG_TEST_RUN command")
> > > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > 
> > That is incorrect fixes tag.
> > It should be pointing to commit f42ee093be29 ("bpf/test_run: support cgroup local storage")
> > 
> > bpf_test_run() can only return the value that bpf program returned.
> > It cannot return -ENOMEM.
> > That code needs to be refactored.
> > I think the proper way for bpf_test_run() would be to return 0 or -ENOMEM
> > and store bpf's retval into extra pointer.
> > Proper checks need to be added in the callers (bpf_prog_test_run_skb, etc).
> 
> Makes total sense. How about this patch?

Thanks for the quick fix!

> Thanks!
> 
> --
> 
> From a2832f56c621d7809da8d4196877fa01621055f5 Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <guro@...com>
> Date: Sat, 1 Dec 2018 10:39:44 -0800
> Subject: [PATCH bpf] bpf: refactor bpf_test_run() to separate own failures and
>  test program result
> 
> After commit f42ee093be29 ("bpf/test_run: support cgroup local
> storage") the bpf_test_run() function may fail with -ENOMEM, if
> it's not possible to allocate memory for a cgroup local storage.
> 
> This error shouldn't be mixed with the return value of the testing
> program. Let's add an additional argument with a pointer where to
> store the testing program's result; and make bpf_test_run()
> return either 0 or -ENOMEM.
> 
> Fixes: f42ee093be29 ("bpf/test_run: support cgroup local storage")
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Suggested-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Roman Gushchin <guro@...com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Alexei Starovoitov <ast@...nel.org>
> ---
>  net/bpf/test_run.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index c89c22c49015..8bce7d8d00d9 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -28,12 +28,13 @@ static __always_inline u32 bpf_test_run_one(struct bpf_prog *prog, void *ctx,
>  	return ret;
>  }
>  
> -static u32 bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *time)
> +static u32 bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *ret,
> +			u32 *time)

may be 'int' return value?

>  {
>  	struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = { 0 };
>  	enum bpf_cgroup_storage_type stype;
>  	u64 time_start, time_spent = 0;
> -	u32 ret = 0, i;
> +	u32 i;
>  
>  	for_each_cgroup_storage_type(stype) {
>  		storage[stype] = bpf_cgroup_storage_alloc(prog, stype);
> @@ -49,7 +50,7 @@ static u32 bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *time)
>  		repeat = 1;
>  	time_start = ktime_get_ns();
>  	for (i = 0; i < repeat; i++) {
> -		ret = bpf_test_run_one(prog, ctx, storage);
> +		*ret = bpf_test_run_one(prog, ctx, storage);
>  		if (need_resched()) {
>  			if (signal_pending(current))
>  				break;
> @@ -65,7 +66,7 @@ static u32 bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *time)
>  	for_each_cgroup_storage_type(stype)
>  		bpf_cgroup_storage_free(storage[stype]);
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static int bpf_test_finish(const union bpf_attr *kattr,
> @@ -165,7 +166,12 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>  		__skb_push(skb, hh_len);
>  	if (is_direct_pkt_access)
>  		bpf_compute_data_pointers(skb);
> -	retval = bpf_test_run(prog, skb, repeat, &duration);
> +	ret = bpf_test_run(prog, skb, repeat, &retval, &duration);
> +	if (ret) {
> +		kfree(data);

should probably be kfree_skb(skb); instead ?

> +		kfree(sk);
> +		return ret;
> +	}
>  	if (!is_l2) {
>  		if (skb_headroom(skb) < hh_len) {
>  			int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
> @@ -212,11 +218,14 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
>  	rxqueue = __netif_get_rx_queue(current->nsproxy->net_ns->loopback_dev, 0);
>  	xdp.rxq = &rxqueue->xdp_rxq;
>  
> -	retval = bpf_test_run(prog, &xdp, repeat, &duration);
> +	ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration);
> +	if (ret)
> +		goto out;
>  	if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN ||
>  	    xdp.data_end != xdp.data + size)
>  		size = xdp.data_end - xdp.data;
>  	ret = bpf_test_finish(kattr, uattr, xdp.data, size, retval, duration);
> +out:
>  	kfree(data);
>  	return ret;
>  }
> -- 
> 2.17.2
>