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bpf: a bug fix and test cases for bpf_skb_change_tail() #4722

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bpf: a bug fix and test cases for bpf_skb_change_tail() #4722

wants to merge 4 commits into from

Commits on Dec 6, 2024

  1. bpf: Check negative offsets in __bpf_skb_min_len() 

    skb_network_offset() and skb_transport_offset() can be negative when
they are called after we pull the transport header, for example, when
we use eBPF sockmap at the point of ->sk_data_ready().

__bpf_skb_min_len() uses an unsigned int to get these offsets, this
leads to a very large number which then causes bpf_skb_change_tail()
failed unexpectedly.

Fix this by using a signed int to get these offsets and ensure the
minimum is at least zero.

Fixes: 5293efe ("bpf: add bpf_skb_change_tail helper")
Cc: John Fastabend <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
    Cong Wang authored and Kernel Patches Daemon committed Dec 6, 2024
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  2. selftests/bpf: Add a BPF selftest for bpf_skb_change_tail() 

    As requested by Daniel, we need to add a selftest to cover
bpf_skb_change_tail() cases in skb_verdict. Here we test trimming,
growing and error cases, and validate its expected return values and the
expected sizes of the payload.

Cc: John Fastabend <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Zijian Zhang <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
    Cong Wang authored and Kernel Patches Daemon committed Dec 6, 2024
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  3. selftests/bpf: Introduce socket_helpers.h for TC tests 

    Pull socket helpers out of sockmap_helpers.h so that they can be reused
for TC tests as well. This prepares for the next patch.

Cc: John Fastabend <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Zijian Zhang <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
    Cong Wang authored and Kernel Patches Daemon committed Dec 6, 2024
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  4. selftests/bpf: Test bpf_skb_change_tail() in TC ingress 

    Similarly to the previous test, we also need a test case to cover
positive offsets as well, TC is an excellent hook for this.

Cc: John Fastabend <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Zijian Zhang <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
    Cong Wang authored and Kernel Patches Daemon committed Dec 6, 2024
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