bpf: Allow bpf_dynptr_from_skb() for tp_btf

Making tp_btf able to use bpf_dynptr_from_skb(), which is useful for skb
parsing, especially for non-linear paged skb data. This is achieved by
adding KF_TRUSTED_ARGS flag to bpf_dynptr_from_skb and registering it
for TRACING progs. With KF_TRUSTED_ARGS, args from fentry/fexit are
excluded, so that unsafe progs like fexit/__kfree_skb are not allowed.

We also need the skb dynptr to be read-only in tp_btf. Because
may_access_direct_pkt_data() returns false by default when checking
bpf_dynptr_from_skb, there is no need to add BPF_PROG_TYPE_TRACING to it
explicitly.

Suggested-by: Martin KaFai Lau <martin.lau@linux.dev>
Signed-off-by: Philo Lu <lulie@linux.alibaba.com>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240911033719.91468-5-lulie@linux.alibaba.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/net/core/filter.c b/net/core/filter.c
index f09d875cc05318d06bfb11f5bb7c62dcdc4fbb97..c6012a3a14b20a010049e9be384030f7fce9fbc6 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12063,7 +12063,7 @@ int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
 }
 
 BTF_KFUNCS_START(bpf_kfunc_check_set_skb)
-BTF_ID_FLAGS(func, bpf_dynptr_from_skb)
+BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_kfunc_check_set_skb)
 
 BTF_KFUNCS_START(bpf_kfunc_check_set_xdp)
@@ -12112,6 +12112,7 @@ static int __init bpf_kfunc_init(void)
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_XMIT, &bpf_kfunc_set_skb);
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_NETFILTER, &bpf_kfunc_set_skb);
+       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_kfunc_set_skb);
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
        ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
                                               &bpf_kfunc_set_sock_addr);