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Date:   Thu, 20 Aug 2020 17:28:03 -0700
From:   Udip Pant <>
To:     Udip Pant <>, Alexei Starovoitov <>,
        Martin KaFai Lau <>,
        Song Liu <>, Yonghong Song <>,
        Andrii Nakryiko <>,
        "David S . Miller" <>
CC:     <>, <>,
Subject: [PATCH v2 bpf 1/2] bpf: verifier: check for packet data access based on target prog

While using dynamic program extension (of type BPF_PROG_TYPE_EXT), we
need to check the program type of the target program to grant the read /
write access to the packet data.

The BPF_PROG_TYPE_EXT type can be used to extend types such as XDP, SKB
and others. Since the BPF_PROG_TYPE_EXT program type on itself is just a
placeholder for those, we need this extended check for those target
programs to actually work while using this option.

Tested this with a freplace xdp program. Without this patch, the
verifier fails with error 'cannot write into packet'.

Signed-off-by: Udip Pant <>
 kernel/bpf/verifier.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ef938f17b944..4d7604430994 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2629,7 +2629,11 @@ static bool may_access_direct_pkt_data(struct bpf_verifier_env *env,
 				       const struct bpf_call_arg_meta *meta,
 				       enum bpf_access_type t)
-	switch (env->prog->type) {
+	struct bpf_prog *prog = env->prog;
+	enum bpf_prog_type prog_type = prog->aux->linked_prog ?
+	      prog->aux->linked_prog->type : prog->type;
+	switch (prog_type) {
 	/* Program types only with direct read access go here! */

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