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selftests/bpf: Cover read/write to skb metadata at an offset

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Exercise r/w access to skb metadata through an offset-adjusted dynptr,
read/write helper with an offset argument, and a slice starting at an
offset.

Also check for the expected errors when the offset is out of bounds.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Jesse Brandeburg <jbrandeburg@cloudflare.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://patch.msgid.link/20250814-skb-metadata-thru-dynptr-v7-8-8a39e636e0fb@cloudflare.com
This commit is contained in:
Jakub Sitnicki 2025-08-14 11:59:34 +02:00 committed by Martin KaFai Lau
parent ed93360807
commit bd1b51b319
2 changed files with 129 additions and 0 deletions
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10
tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
View File

@ -375,6 +375,16 @@ void test_xdp_context_tuntap(void)
skel->progs.ing_cls_dynptr_slice_rdwr,
skel->progs.ing_cls_dynptr_slice,
skel->maps.test_result);
if (test__start_subtest("dynptr_offset"))
test_tuntap(skel->progs.ing_xdp_zalloc_meta,
skel->progs.ing_cls_dynptr_offset_wr,
skel->progs.ing_cls_dynptr_offset_rd,
skel->maps.test_result);
if (test__start_subtest("dynptr_offset_oob"))
test_tuntap(skel->progs.ing_xdp,
skel->progs.ing_cls_dynptr_offset_oob,
skel->progs.ing_cls,
skel->maps.test_result);
test_xdp_meta__destroy(skel);
}

119
tools/testing/selftests/bpf/progs/test_xdp_meta.c
View File

@ -1,5 +1,6 @@
#include <stdbool.h>
#include <linux/bpf.h>
#include <linux/errno.h>
#include <linux/if_ether.h>
#include <linux/pkt_cls.h>
@ -122,6 +123,124 @@ int ing_cls_dynptr_slice_rdwr(struct __sk_buff *ctx)
return TC_ACT_UNSPEC; /* pass */
}
/* Read skb metadata in chunks from various offsets in different ways. */
SEC("tc")
int ing_cls_dynptr_offset_rd(struct __sk_buff *ctx)
{
struct bpf_dynptr meta;
const __u32 chunk_len = META_SIZE / 4;
const __u32 zero = 0;
__u8 *dst, *src;
dst = bpf_map_lookup_elem(&test_result, &zero);
if (!dst)
return TC_ACT_SHOT;
/* 1. Regular read */
bpf_dynptr_from_skb_meta(ctx, 0, &meta);
bpf_dynptr_read(dst, chunk_len, &meta, 0, 0);
dst += chunk_len;
/* 2. Read from an offset-adjusted dynptr */
bpf_dynptr_adjust(&meta, chunk_len, bpf_dynptr_size(&meta));
bpf_dynptr_read(dst, chunk_len, &meta, 0, 0);
dst += chunk_len;
/* 3. Read at an offset */
bpf_dynptr_read(dst, chunk_len, &meta, chunk_len, 0);
dst += chunk_len;
/* 4. Read from a slice starting at an offset */
src = bpf_dynptr_slice(&meta, 2 * chunk_len, NULL, chunk_len);
if (!src)
return TC_ACT_SHOT;
__builtin_memcpy(dst, src, chunk_len);
return TC_ACT_SHOT;
}
/* Write skb metadata in chunks at various offsets in different ways. */
SEC("tc")
int ing_cls_dynptr_offset_wr(struct __sk_buff *ctx)
{
const __u32 chunk_len = META_SIZE / 4;
__u8 payload[META_SIZE];
struct bpf_dynptr meta;
__u8 *dst, *src;
bpf_skb_load_bytes(ctx, sizeof(struct ethhdr), payload, sizeof(payload));
src = payload;
/* 1. Regular write */
bpf_dynptr_from_skb_meta(ctx, 0, &meta);
bpf_dynptr_write(&meta, 0, src, chunk_len, 0);
src += chunk_len;
/* 2. Write to an offset-adjusted dynptr */
bpf_dynptr_adjust(&meta, chunk_len, bpf_dynptr_size(&meta));
bpf_dynptr_write(&meta, 0, src, chunk_len, 0);
src += chunk_len;
/* 3. Write at an offset */
bpf_dynptr_write(&meta, chunk_len, src, chunk_len, 0);
src += chunk_len;
/* 4. Write to a slice starting at an offset */
dst = bpf_dynptr_slice_rdwr(&meta, 2 * chunk_len, NULL, chunk_len);
if (!dst)
return TC_ACT_SHOT;
__builtin_memcpy(dst, src, chunk_len);
return TC_ACT_UNSPEC; /* pass */
}
/* Pass an OOB offset to dynptr read, write, adjust, slice. */
SEC("tc")
int ing_cls_dynptr_offset_oob(struct __sk_buff *ctx)
{
struct bpf_dynptr meta;
__u8 md, *p;
int err;
err = bpf_dynptr_from_skb_meta(ctx, 0, &meta);
if (err)
goto fail;
/* read offset OOB */
err = bpf_dynptr_read(&md, sizeof(md), &meta, META_SIZE, 0);
if (err != -E2BIG)
goto fail;
/* write offset OOB */
err = bpf_dynptr_write(&meta, META_SIZE, &md, sizeof(md), 0);
if (err != -E2BIG)
goto fail;
/* adjust end offset OOB */
err = bpf_dynptr_adjust(&meta, 0, META_SIZE + 1);
if (err != -ERANGE)
goto fail;
/* adjust start offset OOB */
err = bpf_dynptr_adjust(&meta, META_SIZE + 1, META_SIZE + 1);
if (err != -ERANGE)
goto fail;
/* slice offset OOB */
p = bpf_dynptr_slice(&meta, META_SIZE, NULL, sizeof(*p));
if (p)
goto fail;
/* slice rdwr offset OOB */
p = bpf_dynptr_slice_rdwr(&meta, META_SIZE, NULL, sizeof(*p));
if (p)
goto fail;
return TC_ACT_UNSPEC;
fail:
return TC_ACT_SHOT;
}
/* Reserve and clear space for metadata but don't populate it */
SEC("xdp")
int ing_xdp_zalloc_meta(struct xdp_md *ctx)