selftests/bpf: don't modify the skb in the strparser parser prog

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sockmap_parse_prog.c is attached as an SK_SKB stream parser and modifies
the skb: it calls bpf_skb_pull_data() and writes a byte into the packet.
A stream parser runs on strparser's message head and must not modify it.
A resize frees the frag_list segments strparser still tracks, leading to
a use-after-free.

Make the parser read-only. It only needs to return the message length,
which keeps it attaching once packet-modifying parsers are rejected.

Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Sechang Lim <rhkrqnwk98@gmail.com>
Link: https://lore.kernel.org/r/20260620024423.4141004-2-rhkrqnwk98@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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Sechang Lim 2026-06-20 02:44:16 +00:00 • committed by Alexei Starovoitov

parent 4edcdefd40

commit 22a0cc10da

1 changed files with 0 additions and 22 deletions

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tools/testing/selftests/bpf/progs/sockmap_parse_prog.c

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