98589a0998
Commit 2c16d60332 ("netfilter: xt_bpf: support ebpf") introduced
support for attaching an eBPF object by an fd, with the
'bpf_mt_check_v1' ABI expecting the '.fd' to be specified upon each
IPT_SO_SET_REPLACE call.
However this breaks subsequent iptables calls:
# iptables -A INPUT -m bpf --object-pinned /sys/fs/bpf/xxx -j ACCEPT
# iptables -A INPUT -s 5.6.7.8 -j ACCEPT
iptables: Invalid argument. Run `dmesg' for more information.
That's because iptables works by loading existing rules using
IPT_SO_GET_ENTRIES to userspace, then issuing IPT_SO_SET_REPLACE with
the replacement set.
However, the loaded 'xt_bpf_info_v1' has an arbitrary '.fd' number
(from the initial "iptables -m bpf" invocation) - so when 2nd invocation
occurs, userspace passes a bogus fd number, which leads to
'bpf_mt_check_v1' to fail.
One suggested solution [1] was to hack iptables userspace, to perform a
"entries fixup" immediatley after IPT_SO_GET_ENTRIES, by opening a new,
process-local fd per every 'xt_bpf_info_v1' entry seen.
However, in [2] both Pablo Neira Ayuso and Willem de Bruijn suggested to
depricate the xt_bpf_info_v1 ABI dealing with pinned ebpf objects.
This fix changes the XT_BPF_MODE_FD_PINNED behavior to ignore the given
'.fd' and instead perform an in-kernel lookup for the bpf object given
the provided '.path'.
It also defines an alias for the XT_BPF_MODE_FD_PINNED mode, named
XT_BPF_MODE_PATH_PINNED, to better reflect the fact that the user is
expected to provide the path of the pinned object.
Existing XT_BPF_MODE_FD_ELF behavior (non-pinned fd mode) is preserved.
References: [1] https://marc.info/?l=netfilter-devel&m=150564724607440&w=2
[2] https://marc.info/?l=netfilter-devel&m=150575727129880&w=2
Reported-by: Rafael Buchbinder <rafi@rbk.ms>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
42 lines
872 B
C
42 lines
872 B
C
#ifndef _XT_BPF_H
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#define _XT_BPF_H
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#include <linux/filter.h>
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#include <linux/limits.h>
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#include <linux/types.h>
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#define XT_BPF_MAX_NUM_INSTR 64
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#define XT_BPF_PATH_MAX (XT_BPF_MAX_NUM_INSTR * sizeof(struct sock_filter))
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struct bpf_prog;
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struct xt_bpf_info {
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__u16 bpf_program_num_elem;
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struct sock_filter bpf_program[XT_BPF_MAX_NUM_INSTR];
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/* only used in the kernel */
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struct bpf_prog *filter __attribute__((aligned(8)));
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};
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enum xt_bpf_modes {
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XT_BPF_MODE_BYTECODE,
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XT_BPF_MODE_FD_PINNED,
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XT_BPF_MODE_FD_ELF,
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};
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#define XT_BPF_MODE_PATH_PINNED XT_BPF_MODE_FD_PINNED
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struct xt_bpf_info_v1 {
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__u16 mode;
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__u16 bpf_program_num_elem;
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__s32 fd;
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union {
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struct sock_filter bpf_program[XT_BPF_MAX_NUM_INSTR];
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char path[XT_BPF_PATH_MAX];
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};
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/* only used in the kernel */
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struct bpf_prog *filter __attribute__((aligned(8)));
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};
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#endif /*_XT_BPF_H */
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