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bpf: Clarify the meaning of BPF_F_PSEUDO_HDR

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In the bpf_l4_csum_replace helper, the BPF_F_PSEUDO_HDR flag should only
be set if the modified header field is part of the pseudo-header.

If you modify for example the UDP ports and pass BPF_F_PSEUDO_HDR,
inet_proto_csum_replace4 will update skb->csum even though it shouldn't
(the port and the UDP checksum updates null each other).

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/5126ef84ba75425b689482cbc98bffe75e5d8ab0.1744102490.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Paul Chaignon
2025-04-08 11:00:51 +02:00
committed by Andrii Nakryiko
parent 7de6a44a0f
commit 0c85f5a154
1 changed files with 1 additions and 1 deletions
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2
include/uapi/linux/bpf.h
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@@ -2055,7 +2055,7 @@ union bpf_attr {
* untouched (unless **BPF_F_MARK_ENFORCE** is added as well), and * untouched (unless **BPF_F_MARK_ENFORCE** is added as well), and
* for updates resulting in a null checksum the value is set to * for updates resulting in a null checksum the value is set to
* **CSUM_MANGLED_0** instead. Flag **BPF_F_PSEUDO_HDR** indicates * **CSUM_MANGLED_0** instead. Flag **BPF_F_PSEUDO_HDR** indicates
* the checksum is to be computed against a pseudo-header. * that the modified header field is part of the pseudo-header.
* *
* This helper works in combination with **bpf_csum_diff**\ (), * This helper works in combination with **bpf_csum_diff**\ (),
* which does not update the checksum in-place, but offers more * which does not update the checksum in-place, but offers more