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bpf: Reject pkt arguments in mutating subprogs

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The verifier tracks changes in how PTR_TO_PACKET registers'
bounds are modified across subprog boundaries. PTR_TO_PACKET
registers are actually passed as PTR_TO_MEM, which is assumed
valid for the entire call. This is not the case with packet memory,
where a pskb_* call may invalidate its memory region.

Reject BPF code that passes PTR_TO_PACKET pointers to subprogs that
may mutate a packet. We cannot pass the pointer as a true PTR_TO_PACKET
because we would also need to somehow pass the PTR_TO_PACKET_META
or PTR_TO_PACKET_END to the subprog. Since we cannot avoid representing
the pointer in the subprog as PTR_TO_MEM, only permit it if the
subprog is guaranteed not to mutate the packet.

Fixes: 80f281664f5a ("bpf: Support pointers in global func args")
Reported-by: Nicholas Carlini <nicholas@carlini.com>
Suggested-by: Nicholas Carlini <nicholas@carlini.com>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20260922172028.6269-6-emil@etsalapatis.com
This commit is contained in:
Emil Tsalapatis 2026-09-22 17:20:22 +00:00 committed by Alexei Starovoitov
parent dec0c209a6
commit a6c1edfbe2
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1 changed files with 10 additions and 0 deletions
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10
kernel/bpf/verifier.c
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@ -9750,6 +9750,16 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
if (check_mem_reg(env, reg, argno, arg->mem_size, BPF_READ | BPF_WRITE, NULL,
NULL))
return -EINVAL;
/*
* PTR_TO_PACKET get passed as PTR_TO_MEM, preventing
* us from adjusting bounds tracking info.
*/
if ((reg_is_pkt_pointer_any(reg) || reg_is_dynptr_slice_pkt(reg)) &&
sub->changes_pkt_data) {
bpf_log(log, "%s is a packet pointer, but func#%d may change packet data\n",
reg_arg_name(env, argno), subprog);
return -EINVAL;
}
if (!(arg->arg_type & PTR_MAYBE_NULL) &&
(type_may_be_null(reg->type) || bpf_register_is_null(reg))) {
bpf_log(log, "%s is expected to be non-NULL\n",