netdev - [PATCH net-next 1/1] selftests: drv-net: Reload pkt pointer after calling filter

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Message-ID: <20250925161452.1290694-1-ameryhung@gmail.com>
Date: Thu, 25 Sep 2025 09:14:52 -0700
From: Amery Hung <ameryhung@...il.com>
To: netdev@...r.kernel.org
Cc: bpf@...r.kernel.org,
	davem@...emloft.net,
	edumazet@...gle.com,
	pabeni@...hat.com,
	kuba@...nel.org,
	alexei.starovoitov@...il.com,
	andrii@...nel.org,
	daniel@...earbox.net,
	martin.lau@...nel.org,
	stfomichev@...il.com,
	kernel-team@...a.com
Subject: [PATCH net-next 1/1] selftests: drv-net: Reload pkt pointer after calling filter_udphdr

Fix a verification failure. filter_udphdr() calls bpf_xdp_pull_data(),
which will invalidate all pkt pointers. Therefore, all ctx->data loaded
before filter_udphdr() cannot be used. Reload it to prevent verification
errors.

The error may not appear on some compiler versions if they decide to
load ctx->data after filter_udphdr() when it is first used.

Fixes: efec2e55bdef ("selftests: drv-net: Pull data before parsing headers")
Signed-off-by: Amery Hung <ameryhung@...il.com>
---
 tools/testing/selftests/net/lib/xdp_native.bpf.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/net/lib/xdp_native.bpf.c b/tools/testing/selftests/net/lib/xdp_native.bpf.c
index df4eea5c192b..c368fc045f4b 100644
--- a/tools/testing/selftests/net/lib/xdp_native.bpf.c
+++ b/tools/testing/selftests/net/lib/xdp_native.bpf.c
@@ -420,7 +420,6 @@ static int xdp_adjst_tail_grow_data(struct xdp_md *ctx, __u16 offset)
 
 static int xdp_adjst_tail(struct xdp_md *ctx, __u16 port)
 {
-	void *data = (void *)(long)ctx->data;
 	struct udphdr *udph = NULL;
 	__s32 *adjust_offset, *val;
 	__u32 key, hdr_len;
@@ -432,7 +431,8 @@ static int xdp_adjst_tail(struct xdp_md *ctx, __u16 port)
 	if (!udph)
 		return XDP_PASS;
 
-	hdr_len = (void *)udph - data + sizeof(struct udphdr);
+	hdr_len = (void *)udph - (void *)(long)ctx->data +
+		  sizeof(struct udphdr);
 	key = XDP_ADJST_OFFSET;
 	adjust_offset = bpf_map_lookup_elem(&map_xdp_setup, &key);
 	if (!adjust_offset)
@@ -572,8 +572,6 @@ static int xdp_adjst_head_grow_data(struct xdp_md *ctx, __u64 hdr_len,
 
 static int xdp_head_adjst(struct xdp_md *ctx, __u16 port)
 {
-	void *data_end = (void *)(long)ctx->data_end;
-	void *data = (void *)(long)ctx->data;
 	struct udphdr *udph_ptr = NULL;
 	__u32 key, size, hdr_len;
 	__s32 *val;
@@ -584,7 +582,8 @@ static int xdp_head_adjst(struct xdp_md *ctx, __u16 port)
 	if (!udph_ptr)
 		return XDP_PASS;
 
-	hdr_len = (void *)udph_ptr - data + sizeof(struct udphdr);
+	hdr_len = (void *)udph_ptr - (void *)(long)ctx->data +
+		  sizeof(struct udphdr);
 
 	key = XDP_ADJST_OFFSET;
 	val = bpf_map_lookup_elem(&map_xdp_setup, &key);
-- 
2.47.3