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1a4607ffba
Tail-called programs could execute any of the helpers that invalidate
packet pointers. Hence, conservatively assume that each tail call
invalidates packet pointers.
Making the change in bpf_helper_changes_pkt_data() automatically makes
use of check_cfg() logic that computes 'changes_pkt_data' effect for
global sub-programs, such that the following program could be
rejected:
int tail_call(struct __sk_buff *sk)
{
bpf_tail_call_static(sk, &jmp_table, 0);
return 0;
}
SEC("tc")
int not_safe(struct __sk_buff *sk)
{
int *p = (void *)(long)sk->data;
... make p valid ...
tail_call(sk);
*p = 42; /* this is unsafe */
...
}
The tc_bpf2bpf.c:subprog_tc() needs change: mark it as a function that
can invalidate packet pointers. Otherwise, it can't be freplaced with
tailcall_freplace.c:entry_freplace() that does a tail call.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20241210041100.1898468-8-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
25 lines
449 B
C
25 lines
449 B
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include "bpf_misc.h"
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__noinline
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int subprog_tc(struct __sk_buff *skb)
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{
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int ret = 1;
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__sink(skb);
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__sink(ret);
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/* let verifier know that 'subprog_tc' can change pointers to skb->data */
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bpf_skb_change_proto(skb, 0, 0);
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return ret;
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}
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SEC("tc")
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int entry_tc(struct __sk_buff *skb)
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{
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return subprog_tc(skb);
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}
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char __license[] SEC("license") = "GPL";
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