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082f1db02c
Certain bpf syscall subcommands are available for usage from both userspace and the kernel. LSM modules or eBPF gatekeeper programs may need to take a different course of action depending on whether or not a BPF syscall originated from the kernel or userspace. Additionally, some of the bpf_attr struct fields contain pointers to arbitrary memory. Currently the functionality to determine whether or not a pointer refers to kernel memory or userspace memory is exposed to the bpf verifier, but that information is missing from various LSM hooks. Here we augment the LSM hooks to provide this data, by simply passing a boolean flag indicating whether or not the call originated in the kernel, in any hook that contains a bpf_attr struct that corresponds to a subcommand that may be called from the kernel. Signed-off-by: Blaise Boscaccy <bboscaccy@linux.microsoft.com> Acked-by: Song Liu <song@kernel.org> Acked-by: Paul Moore <paul@paul-moore.com> Link: https://lore.kernel.org/r/20250310221737.821889-2-bboscaccy@linux.microsoft.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
71 lines
1.6 KiB
C
71 lines
1.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (C) 2023 Yafang Shao <laoar.shao@gmail.com> */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_core_read.h>
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__u32 target_ancestor_level;
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__u64 target_ancestor_cgid;
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int target_pid, target_hid;
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struct cgroup *bpf_task_get_cgroup1(struct task_struct *task, int hierarchy_id) __ksym;
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struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) __ksym;
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void bpf_cgroup_release(struct cgroup *cgrp) __ksym;
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static int bpf_link_create_verify(int cmd)
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{
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struct cgroup *cgrp, *ancestor;
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struct task_struct *task;
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int ret = 0;
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if (cmd != BPF_LINK_CREATE)
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return 0;
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task = bpf_get_current_task_btf();
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/* Then it can run in parallel with others */
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if (task->pid != target_pid)
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return 0;
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cgrp = bpf_task_get_cgroup1(task, target_hid);
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if (!cgrp)
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return 0;
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/* Refuse it if its cgid or its ancestor's cgid is the target cgid */
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if (cgrp->kn->id == target_ancestor_cgid)
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ret = -1;
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ancestor = bpf_cgroup_ancestor(cgrp, target_ancestor_level);
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if (!ancestor)
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goto out;
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if (ancestor->kn->id == target_ancestor_cgid)
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ret = -1;
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bpf_cgroup_release(ancestor);
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out:
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bpf_cgroup_release(cgrp);
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return ret;
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}
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SEC("lsm/bpf")
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int BPF_PROG(lsm_run, int cmd, union bpf_attr *attr, unsigned int size, bool kernel)
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{
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return bpf_link_create_verify(cmd);
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}
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SEC("lsm.s/bpf")
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int BPF_PROG(lsm_s_run, int cmd, union bpf_attr *attr, unsigned int size, bool kernel)
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{
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return bpf_link_create_verify(cmd);
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}
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SEC("fentry")
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int BPF_PROG(fentry_run)
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{
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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