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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>
This commit is contained in:
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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22
tools/testing/selftests/bpf/progs/sockmap_parse_prog.c
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@ -5,28 +5,6 @@
SEC("sk_skb1")
int bpf_prog1(struct __sk_buff *skb)
{
void *data_end = (void *)(long) skb->data_end;
void *data = (void *)(long) skb->data;
__u8 *d = data;
int err;
if (data + 10 > data_end) {
err = bpf_skb_pull_data(skb, 10);
if (err)
return SK_DROP;
data_end = (void *)(long)skb->data_end;
data = (void *)(long)skb->data;
if (data + 10 > data_end)
return SK_DROP;
}
/* This write/read is a bit pointless but tests the verifier and
* strparser handler for read/write pkt data and access into sk
* fields.
*/
d = data;
d[7] = 1;
return skb->len;
}