Make TC BPF helpers preserve skb metadata #6066
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pskb_expand_head() copies headroom (including skb metadata) into the newly allocated head, but then clears the metadata. As a result, metadata is lost when BPF helpers trigger a headroom reallocation. Let the skb metadata be in the newly created copy of head. Signed-off-by: Jakub Sitnicki <[email protected]>
Lay groundwork for fixing BPF helpers available to TC(X) programs. When skb_push() or skb_pull() is called in a TC(X) ingress BPF program, the skb metadata must be kept in front of the MAC header. Otherwise, BPF programs using the __sk_buff->data_meta pseudo-pointer lose access to it. Introduce a helper that moves both metadata and a specified number of packet data bytes together, suitable as a drop-in replacement for memmove(). Signed-off-by: Jakub Sitnicki <[email protected]>
All callers ignore the return value. Prepare to reorder memmove() after skb_pull() which is a common pattern. Signed-off-by: Jakub Sitnicki <[email protected]>
Use the metadata-aware helper to move packet bytes after skb_pull(), ensuring metadata remains valid after calling the BPF helper. Signed-off-by: Jakub Sitnicki <[email protected]>
Use the metadata-aware helper to move packet bytes after skb_push(), ensuring metadata remains valid after calling the BPF helper. Also, take care to reserve sufficient headroom for metadata to fit. Signed-off-by: Jakub Sitnicki <[email protected]>
bpf_skb_adjust_room() may push or pull bytes from skb->data. In both cases, skb metadata must be moved accordingly to stay accessible. Replace existing memmove() calls, which only move payload, with a helper that also handles metadata. Reserve enough space for metadata to fit after skb_push. Signed-off-by: Jakub Sitnicki <[email protected]>
bpf_skb_change_proto reuses the same headroom operations as bpf_skb_adjust_room, already updated to handle metadata safely. The remaining step is to ensure that there is sufficient headroom to accommodate metadata on skb_push(). Signed-off-by: Jakub Sitnicki <[email protected]>
Although bpf_skb_change_head() doesn't move packet data after skb_push(), skb metadata still needs to be relocated. Use the dedicated helper to handle it. Signed-off-by: Jakub Sitnicki <[email protected]>
Since pskb_expand_head() no longer clears metadata on unclone, update tests for cloned packets to expect metadata to remain intact. Verify metadata contents directly in the BPF program. This allows for multiple checks as packet passes through a chain of BPF programs, rather than a one-time check in user-space. Signed-off-by: Jakub Sitnicki <[email protected]>
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Upstream branch: 4ef77dd |
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1007107 expired. Closing PR. |
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Pull request for series with
subject: Make TC BPF helpers preserve skb metadata
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1007107