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Date: Tue, 9 Apr 2019 09:08:12 -0700
From: Stanislav Fomichev <sdf@...ichev.me>
To: Martin Lau <kafai@...com>
Cc: Stanislav Fomichev <sdf@...gle.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"davem@...emloft.net" <davem@...emloft.net>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next v2 1/3] bpf: support input __sk_buff context in
BPF_PROG_TEST_RUN
On 04/09, Martin Lau wrote:
> On Mon, Apr 08, 2019 at 09:04:30AM -0700, Stanislav Fomichev wrote:
> > Add new set of arguments to bpf_attr for BPF_PROG_TEST_RUN:
> > * ctx_in/ctx_size_in - input context
> > * ctx_out/ctx_size_out - output context
> >
> > The intended use case is to pass some meta data to the test runs that
> > operate on skb (this has being brought up on recent LPC).
> >
> > For programs that use bpf_prog_test_run_skb, support __sk_buff input and
> > output. Initially, from input __sk_buff, copy _only_ cb and priority into
> > skb, all other non-zero fields are prohibited (with EINVAL).
> > If the user has set ctx_out/ctx_size_out, copy the potentially modified
> > __sk_buff back to the userspace.
> >
> > We require all fields of input __sk_buff except the ones we explicitly
> > support to be set to zero. The expectation is that in the future we might
> > add support for more fields and we want to fail explicitly if the user
> > runs the program on the kernel where we don't yet support them.
> >
> > The API is intentionally vague (i.e. we don't explicitly add __sk_buff
> > to bpf_attr, but ctx_in) to potentially let other test_run types use
> > this interface in the future (this can be xdp_md for xdp types for
> > example).
> >
> > v2:
> > * Addressed comments from Martin Lau
> >
> > Cc: Martin Lau <kafai@...com>
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> > include/uapi/linux/bpf.h | 7 ++
> > kernel/bpf/syscall.c | 10 ++-
> > net/bpf/test_run.c | 135 ++++++++++++++++++++++++++++++++++++---
> > 3 files changed, 143 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 837024512baf..8e96f99cebf8 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -396,6 +396,13 @@ union bpf_attr {
> > __aligned_u64 data_out;
> > __u32 repeat;
> > __u32 duration;
> > + __u32 ctx_size_in; /* input: len of ctx_in */
> > + __u32 ctx_size_out; /* input/output: len of ctx_out
> > + * returns ENOSPC if ctx_out
> > + * is too small.
> > + */
> > + __aligned_u64 ctx_in;
> > + __aligned_u64 ctx_out;
> > } test;
> >
> > struct { /* anonymous struct used by BPF_*_GET_*_ID */
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 1d65e56594db..5bb963e8f9b0 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -1949,7 +1949,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
> > return cgroup_bpf_prog_query(attr, uattr);
> > }
> >
> > -#define BPF_PROG_TEST_RUN_LAST_FIELD test.duration
> > +#define BPF_PROG_TEST_RUN_LAST_FIELD test.ctx_out
> >
> > static int bpf_prog_test_run(const union bpf_attr *attr,
> > union bpf_attr __user *uattr)
> > @@ -1962,6 +1962,14 @@ static int bpf_prog_test_run(const union bpf_attr *attr,
> > if (CHECK_ATTR(BPF_PROG_TEST_RUN))
> > return -EINVAL;
> >
> > + if ((attr->test.ctx_size_in && !attr->test.ctx_in) ||
> > + (!attr->test.ctx_size_in && attr->test.ctx_in))
> > + return -EINVAL;
> > +
> > + if ((attr->test.ctx_size_out && !attr->test.ctx_out) ||
> > + (!attr->test.ctx_size_out && attr->test.ctx_out))
> > + return -EINVAL;
> > +
> > prog = bpf_prog_get(attr->test.prog_fd);
> > if (IS_ERR(prog))
> > return PTR_ERR(prog);
> > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> > index fab142b796ef..3c6e3855c886 100644
> > --- a/net/bpf/test_run.c
> > +++ b/net/bpf/test_run.c
> > @@ -123,12 +123,118 @@ static void *bpf_test_init(const union bpf_attr *kattr, u32 size,
> > return data;
> > }
> >
> > +static void *bpf_ctx_init(const union bpf_attr *kattr, u32 max_size)
> > +{
> > + void __user *data_in = u64_to_user_ptr(kattr->test.ctx_in);
> > + u32 size = kattr->test.ctx_size_in;
> > + void *data;
> > +
> > + if (!size)
> > + return NULL;
> A note for a later comment in bpf_prog_test_run_skb().
> This function may return NULL.
>
> > +
> > + if (size > max_size)
> If should be fine if the kernel unsupported bytes are zeros
> (i.e. tailing zeros in data_in).
> Please refer to the existing bpf_check_uarg_tail_zero() usages
> or also CHECK_ATTR() in syscall.c. Something like this if
> bpf_check_uarg_tail_zero() is used,
>
> err = bpf_check_uarg_tail_zero(data_in, max_size, size));
> if (err)
> return ERR_PTR(err);
>
Nice! Will use that instead.
> > + return ERR_PTR(-E2BIG);
> > +
> > + data = kzalloc(max_size, GFP_USER);
> > + if (!data)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + if (copy_from_user(data, data_in, size)) {
> > + kfree(data);
> > + return ERR_PTR(-EFAULT);
> > + }
> > + return data;
> > +}
> > +
> > +static int bpf_ctx_finish(const union bpf_attr *kattr,
> > + union bpf_attr __user *uattr, const void *data,
> > + u32 size)
> > +{
> > + void __user *data_out = u64_to_user_ptr(kattr->test.ctx_out);
> > + int err = -EFAULT;
> > + u32 copy_size = size;
> > +
> data is not checked for NULL here.
I do check kattr->test.ctx_size_out on the next line. And I've added
checks to the syscall.c that make sure that ctx_size_out and ctx_out
are consistent (i.e. if ctx_size_out is 0, ctx_out is NULL).
Let me instead check kattr->test.ctx_out, that should be more clear.
> > + if (!kattr->test.ctx_size_out)
> > + return 0;
> > +
> > + if (copy_size > kattr->test.ctx_size_out) {
> > + copy_size = kattr->test.ctx_size_out;
> > + err = -ENOSPC;
> > + }
> > +
> > + if (copy_to_user(data_out, data, copy_size))
> > + goto out;
> > + if (copy_to_user(&uattr->test.ctx_size_out, &size, sizeof(size)))
> > + goto out;
> > + if (err != -ENOSPC)
> > + err = 0;
> > +out:
> > + return err;
> > +}
>
> [ ... ]
>
> > int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
> > union bpf_attr __user *uattr)
> > {
> > bool is_l2 = false, is_direct_pkt_access = false;
> > u32 size = kattr->test.data_size_in;
> > u32 repeat = kattr->test.repeat;
> > + struct __sk_buff *ctx = NULL;
> > u32 retval, duration;
> > int hh_len = ETH_HLEN;
> > struct sk_buff *skb;
> > @@ -141,6 +247,12 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
> > if (IS_ERR(data))
> > return PTR_ERR(data);
> >
> > + ctx = bpf_ctx_init(kattr, sizeof(struct __sk_buff));
> > + if (IS_ERR(ctx)) {
> > + kfree(data);
> > + return PTR_ERR(ctx);
> > + }
> > +
> > switch (prog->type) {
> > case BPF_PROG_TYPE_SCHED_CLS:
> > case BPF_PROG_TYPE_SCHED_ACT:
> > @@ -158,6 +270,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
> > sk = kzalloc(sizeof(struct sock), GFP_USER);
> > if (!sk) {
> > kfree(data);
> > + kfree(ctx);
> > return -ENOMEM;
> > }
> > sock_net_set(sk, current->nsproxy->net_ns);
> > @@ -166,6 +279,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
> > skb = build_skb(data, 0);
> > if (!skb) {
> > kfree(data);
> > + kfree(ctx);
> > kfree(sk);
> > return -ENOMEM;
> > }
> > @@ -180,32 +294,37 @@ 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);
> > + ret = convert___skb_to_skb(skb, ctx);
> > + if (ret)
> > + goto out;
> > ret = bpf_test_run(prog, skb, repeat, &retval, &duration);
> > - if (ret) {
> > - kfree_skb(skb);
> > - kfree(sk);
> > - return ret;
> > - }
> > + if (ret)
> > + goto out;
> > if (!is_l2) {
> > if (skb_headroom(skb) < hh_len) {
> > int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
> >
> > if (pskb_expand_head(skb, nhead, 0, GFP_USER)) {
> > - kfree_skb(skb);
> > - kfree(sk);
> > - return -ENOMEM;
> > + ret = -ENOMEM;
> > + goto out;
> > }
> > }
> > memset(__skb_push(skb, hh_len), 0, hh_len);
> > }
> > + convert_skb_to___skb(skb, ctx);
> >
> > size = skb->len;
> > /* bpf program can never convert linear skb to non-linear */
> > if (WARN_ON_ONCE(skb_is_nonlinear(skb)))
> > size = skb_headlen(skb);
> > ret = bpf_test_finish(kattr, uattr, skb->data, size, retval, duration);
> > + if (!ret)
> > + ret = bpf_ctx_finish(kattr, uattr, ctx,
> ctx is not checked for NULL in here either.
Good catch, I didn't think about the case where ctx_in is not set,
but ctx_out is set. Let me handle that in the v3.
Thank you for a review!
>
> > + sizeof(struct __sk_buff));
> > +out:
> > kfree_skb(skb);
> > kfree(sk);
> > + kfree(ctx);
> > return ret;
> > }
> >
> > --
> > 2.21.0.392.gf8f6787159e-goog
> >
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