Subject: Re: [PATCH ipsec-next v1 1/7] bpf: xfrm: Add bpf_xdp_get_xfrm_state() kfunc

From: Yonghong Song <[email-masked]>
Date: Sat, 25 Nov 2023 12:36:29 -0800

On 11/22/23 1:20 PM, Daniel Xu wrote:
> This commit adds an unstable kfunc helper to access internal xfrm_state
> associated with an SA. This is intended to be used for the upcoming
> IPsec pcpu work to assign special pcpu SAs to a particular CPU. In other
> words: for custom software RSS.
>
> That being said, the function that this kfunc wraps is fairly generic
> and used for a lot of xfrm tasks. I'm sure people will find uses
> elsewhere over time.
>
> Co-developed-by: Antony Antony <[email-masked]>
> Signed-off-by: Antony Antony <[email-masked]>
> Signed-off-by: Daniel Xu <[email-masked]>
> ---
>   include/net/xfrm.h        |   9 ++++
>   net/xfrm/Makefile         |   1 +
>   net/xfrm/xfrm_policy.c    |   2 +
>   net/xfrm/xfrm_state_bpf.c | 111 ++++++++++++++++++++++++++++++++++++++
>   4 files changed, 123 insertions(+)
>   create mode 100644 net/xfrm/xfrm_state_bpf.c
>
> diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> index c9bb0f892f55..1d107241b901 100644
> --- a/include/net/xfrm.h
> +++ b/include/net/xfrm.h
> @@ -2190,4 +2190,13 @@ static inline int register_xfrm_interface_bpf(void)
>   
>   #endif
>   
> +#if IS_ENABLED(CONFIG_DEBUG_INFO_BTF)
> +int register_xfrm_state_bpf(void);
> +#else
> +static inline int register_xfrm_state_bpf(void)
> +{
> +	return 0;
> +}
> +#endif
> +
>   #endif	/* _NET_XFRM_H */
> diff --git a/net/xfrm/Makefile b/net/xfrm/Makefile
> index cd47f88921f5..547cec77ba03 100644
> --- a/net/xfrm/Makefile
> +++ b/net/xfrm/Makefile
> @@ -21,3 +21,4 @@ obj-$(CONFIG_XFRM_USER_COMPAT) += xfrm_compat.o
>   obj-$(CONFIG_XFRM_IPCOMP) += xfrm_ipcomp.o
>   obj-$(CONFIG_XFRM_INTERFACE) += xfrm_interface.o
>   obj-$(CONFIG_XFRM_ESPINTCP) += espintcp.o
> +obj-$(CONFIG_DEBUG_INFO_BTF) += xfrm_state_bpf.o
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index c13dc3ef7910..1b7e75159727 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -4218,6 +4218,8 @@ void __init xfrm_init(void)
>   #ifdef CONFIG_XFRM_ESPINTCP
>   	espintcp_init();
>   #endif
> +
> +	register_xfrm_state_bpf();
>   }
>   
>   #ifdef CONFIG_AUDITSYSCALL
> diff --git a/net/xfrm/xfrm_state_bpf.c b/net/xfrm/xfrm_state_bpf.c
> new file mode 100644
> index 000000000000..0c1f2f91125c
> --- /dev/null
> +++ b/net/xfrm/xfrm_state_bpf.c
> @@ -0,0 +1,111 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Unstable XFRM state BPF helpers.
> + *
> + * Note that it is allowed to break compatibility for these functions since the
> + * interface they are exposed through to BPF programs is explicitly unstable.
> + */
> +
> +#include <linux/bpf.h>
> +#include <linux/btf_ids.h>
> +#include <net/xdp.h>
> +#include <net/xfrm.h>
> +
> +/* bpf_xfrm_state_opts - Options for XFRM state lookup helpers
> + *
> + * Members:
> + * @error      - Out parameter, set for any errors encountered
> + *		 Values:
> + *		   -EINVAL - netns_id is less than -1
> + *		   -EINVAL - Passed NULL for opts
> + *		   -EINVAL - opts__sz isn't BPF_XFRM_STATE_OPTS_SZ
> + *		   -ENONET - No network namespace found for netns_id
> + * @netns_id	- Specify the network namespace for lookup
> + *		 Values:
> + *		   BPF_F_CURRENT_NETNS (-1)
> + *		     Use namespace associated with ctx
> + *		   [0, S32_MAX]
> + *		     Network Namespace ID
> + * @mark	- XFRM mark to match on
> + * @daddr	- Destination address to match on
> + * @spi		- Security parameter index to match on
> + * @proto	- L3 protocol to match on
> + * @family	- L3 protocol family to match on
> + */
> +struct bpf_xfrm_state_opts {
> +	s32 error;
> +	s32 netns_id;
> +	u32 mark;
> +	xfrm_address_t daddr;
> +	__be32 spi;
> +	u8 proto;
> +	u16 family;
> +};
> +
> +enum {
> +	BPF_XFRM_STATE_OPTS_SZ = sizeof(struct bpf_xfrm_state_opts),
> +};
> +
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +		  "Global functions as their definitions will be in xfrm_state BTF");
> +
> +/* bpf_xdp_get_xfrm_state - Get XFRM state
> + *
> + * Parameters:
> + * @ctx 	- Pointer to ctx (xdp_md) in XDP program
> + *		    Cannot be NULL
> + * @opts	- Options for lookup (documented above)
> + *		    Cannot be NULL
> + * @opts__sz	- Length of the bpf_xfrm_state_opts structure
> + *		    Must be BPF_XFRM_STATE_OPTS_SZ
> + */
> +__bpf_kfunc struct xfrm_state *
> +bpf_xdp_get_xfrm_state(struct xdp_md *ctx, struct bpf_xfrm_state_opts *opts, u32 opts__sz)
> +{
> +	struct xdp_buff *xdp = (struct xdp_buff *)ctx;
> +	struct net *net = dev_net(xdp->rxq->dev);
> +	struct xfrm_state *x;
> +
> +	if (!opts || opts__sz != BPF_XFRM_STATE_OPTS_SZ) {
> +		opts->error = -EINVAL;

If opts is NULL, obvious we have issue opts->error access.
If opts is not NULL and opts_sz < 4, we also have issue with
opts->error access since it may override some other stuff
on the stack.

In such cases, we do not need to do 'opts->error = -EINVAL'
and can simply 'return NULL'. bpf program won't be able
to check opts->error anyway since the opts is either NULL
or opts_sz < 4.

> +		return NULL;
> +	}
> +
> +	if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS)) {
> +		opts->error = -EINVAL;
> +		return NULL;
> +	}
> +
> +	if (opts->netns_id >= 0) {
> +		net = get_net_ns_by_id(net, opts->netns_id);
> +		if (unlikely(!net)) {
> +			opts->error = -ENONET;
> +			return NULL;
> +		}
> +	}
> +
> +	x = xfrm_state_lookup(net, opts->mark, &opts->daddr, opts->spi,
> +			      opts->proto, opts->family);
> +
> +	if (opts->netns_id >= 0)
> +		put_net(net);
> +
> +	return x;
> +}
> +
> +__diag_pop()

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