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selftests/bpf: Add tests for bpf_cgroup_read_xattr
Add tests for different scenarios with bpf_cgroup_read_xattr: 1. Read cgroup xattr from bpf_cgroup_from_id; 2. Read cgroup xattr from bpf_cgroup_ancestor; 3. Read cgroup xattr from css_iter; 4. Use bpf_cgroup_read_xattr in LSM hook security_socket_connect. 5. Use bpf_cgroup_read_xattr in cgroup program. Signed-off-by: Song Liu <song@kernel.org> Link: https://lore.kernel.org/20250623063854.1896364-5-song@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>
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‎tools/testing/selftests/bpf/bpf_experimental.h‎

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@@ -596,4 +596,7 @@ extern int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) __weak __ksym;
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extern struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it) __weak __ksym;
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extern void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) __weak __ksym;
598598

599+
extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str,
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struct bpf_dynptr *value_p) __weak __ksym;
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599602
#endif

‎tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c‎

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// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
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#include <errno.h>
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#include <fcntl.h>
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#include <sys/stat.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/socket.h>
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#include <sys/xattr.h>
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#include <test_progs.h>
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#include "read_cgroupfs_xattr.skel.h"
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#include "cgroup_read_xattr.skel.h"
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#define CGROUP_FS_ROOT "/sys/fs/cgroup/"
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#define CGROUP_FS_PARENT CGROUP_FS_ROOT "foo/"
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#define CGROUP_FS_CHILD CGROUP_FS_PARENT "bar/"
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static int move_pid_to_cgroup(const char *cgroup_folder, pid_t pid)
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{
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char filename[128];
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char pid_str[64];
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int procs_fd;
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int ret;
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snprintf(filename, sizeof(filename), "%scgroup.procs", cgroup_folder);
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snprintf(pid_str, sizeof(pid_str), "%d", pid);
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procs_fd = open(filename, O_WRONLY | O_APPEND);
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if (!ASSERT_OK_FD(procs_fd, "open"))
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return -1;
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ret = write(procs_fd, pid_str, strlen(pid_str));
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close(procs_fd);
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if (!ASSERT_GT(ret, 0, "write cgroup.procs"))
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return -1;
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return 0;
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}
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static void reset_cgroups_and_lo(void)
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{
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rmdir(CGROUP_FS_CHILD);
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rmdir(CGROUP_FS_PARENT);
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system("ip addr del 1.1.1.1/32 dev lo");
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system("ip link set dev lo down");
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}
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static const char xattr_value_a[] = "bpf_selftest_value_a";
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static const char xattr_value_b[] = "bpf_selftest_value_b";
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static const char xattr_name[] = "user.bpf_test";
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static int setup_cgroups_and_lo(void)
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{
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int err;
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err = mkdir(CGROUP_FS_PARENT, 0755);
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if (!ASSERT_OK(err, "mkdir 1"))
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goto error;
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err = mkdir(CGROUP_FS_CHILD, 0755);
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if (!ASSERT_OK(err, "mkdir 2"))
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goto error;
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err = setxattr(CGROUP_FS_PARENT, xattr_name, xattr_value_a,
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strlen(xattr_value_a) + 1, 0);
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if (!ASSERT_OK(err, "setxattr 1"))
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goto error;
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err = setxattr(CGROUP_FS_CHILD, xattr_name, xattr_value_b,
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strlen(xattr_value_b) + 1, 0);
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if (!ASSERT_OK(err, "setxattr 2"))
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goto error;
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err = system("ip link set dev lo up");
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if (!ASSERT_OK(err, "lo up"))
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goto error;
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err = system("ip addr add 1.1.1.1 dev lo");
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if (!ASSERT_OK(err, "lo addr v4"))
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goto error;
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err = write_sysctl("/proc/sys/net/ipv4/ping_group_range", "0 0");
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if (!ASSERT_OK(err, "write_sysctl"))
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goto error;
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return 0;
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error:
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reset_cgroups_and_lo();
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return err;
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}
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static void test_read_cgroup_xattr(void)
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{
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struct sockaddr_in sa4 = {
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.sin_family = AF_INET,
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.sin_addr.s_addr = htonl(INADDR_LOOPBACK),
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};
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struct read_cgroupfs_xattr *skel = NULL;
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pid_t pid = gettid();
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int sock_fd = -1;
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int connect_fd = -1;
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if (!ASSERT_OK(setup_cgroups_and_lo(), "setup_cgroups_and_lo"))
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return;
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if (!ASSERT_OK(move_pid_to_cgroup(CGROUP_FS_CHILD, pid),
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"move_pid_to_cgroup"))
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goto out;
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skel = read_cgroupfs_xattr__open_and_load();
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if (!ASSERT_OK_PTR(skel, "read_cgroupfs_xattr__open_and_load"))
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goto out;
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skel->bss->target_pid = pid;
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if (!ASSERT_OK(read_cgroupfs_xattr__attach(skel), "read_cgroupfs_xattr__attach"))
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goto out;
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sock_fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP);
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if (!ASSERT_OK_FD(sock_fd, "sock create"))
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goto out;
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connect_fd = connect(sock_fd, &sa4, sizeof(sa4));
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if (!ASSERT_OK_FD(connect_fd, "connect 1"))
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goto out;
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close(connect_fd);
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ASSERT_TRUE(skel->bss->found_value_a, "found_value_a");
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ASSERT_TRUE(skel->bss->found_value_b, "found_value_b");
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out:
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close(connect_fd);
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close(sock_fd);
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read_cgroupfs_xattr__destroy(skel);
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move_pid_to_cgroup(CGROUP_FS_ROOT, pid);
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reset_cgroups_and_lo();
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}
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void test_cgroup_xattr(void)
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{
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RUN_TESTS(cgroup_read_xattr);
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if (test__start_subtest("read_cgroupfs_xattr"))
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test_read_cgroup_xattr();
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}

‎tools/testing/selftests/bpf/progs/cgroup_read_xattr.c‎

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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
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#include <vmlinux.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_core_read.h>
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#include "bpf_experimental.h"
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#include "bpf_misc.h"
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char _license[] SEC("license") = "GPL";
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char value[16];
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static __always_inline void read_xattr(struct cgroup *cgroup)
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{
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struct bpf_dynptr value_ptr;
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bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
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bpf_cgroup_read_xattr(cgroup, "user.bpf_test",
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&value_ptr);
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}
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SEC("lsm.s/socket_connect")
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__success
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int BPF_PROG(trusted_cgroup_ptr_sleepable)
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{
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u64 cgrp_id = bpf_get_current_cgroup_id();
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struct cgroup *cgrp;
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cgrp = bpf_cgroup_from_id(cgrp_id);
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if (!cgrp)
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return 0;
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read_xattr(cgrp);
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bpf_cgroup_release(cgrp);
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return 0;
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}
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SEC("lsm/socket_connect")
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__success
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int BPF_PROG(trusted_cgroup_ptr_non_sleepable)
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{
44+
u64 cgrp_id = bpf_get_current_cgroup_id();
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struct cgroup *cgrp;
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cgrp = bpf_cgroup_from_id(cgrp_id);
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if (!cgrp)
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return 0;
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read_xattr(cgrp);
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bpf_cgroup_release(cgrp);
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return 0;
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}
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SEC("lsm/socket_connect")
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__success
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int BPF_PROG(use_css_iter_non_sleepable)
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{
60+
u64 cgrp_id = bpf_get_current_cgroup_id();
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struct cgroup_subsys_state *css;
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struct cgroup *cgrp;
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cgrp = bpf_cgroup_from_id(cgrp_id);
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if (!cgrp)
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return 0;
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bpf_for_each(css, css, &cgrp->self, BPF_CGROUP_ITER_ANCESTORS_UP)
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read_xattr(css->cgroup);
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bpf_cgroup_release(cgrp);
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return 0;
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}
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SEC("lsm.s/socket_connect")
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__failure __msg("expected an RCU CS")
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int BPF_PROG(use_css_iter_sleepable_missing_rcu_lock)
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{
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u64 cgrp_id = bpf_get_current_cgroup_id();
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struct cgroup_subsys_state *css;
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struct cgroup *cgrp;
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cgrp = bpf_cgroup_from_id(cgrp_id);
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if (!cgrp)
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return 0;
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bpf_for_each(css, css, &cgrp->self, BPF_CGROUP_ITER_ANCESTORS_UP)
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read_xattr(css->cgroup);
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bpf_cgroup_release(cgrp);
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return 0;
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}
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SEC("lsm.s/socket_connect")
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__success
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int BPF_PROG(use_css_iter_sleepable_with_rcu_lock)
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{
98+
u64 cgrp_id = bpf_get_current_cgroup_id();
99+
struct cgroup_subsys_state *css;
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struct cgroup *cgrp;
101+
102+
bpf_rcu_read_lock();
103+
cgrp = bpf_cgroup_from_id(cgrp_id);
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if (!cgrp)
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goto out;
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bpf_for_each(css, css, &cgrp->self, BPF_CGROUP_ITER_ANCESTORS_UP)
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read_xattr(css->cgroup);
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bpf_cgroup_release(cgrp);
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out:
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bpf_rcu_read_unlock();
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return 0;
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}
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SEC("lsm/socket_connect")
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__success
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int BPF_PROG(use_bpf_cgroup_ancestor)
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{
120+
u64 cgrp_id = bpf_get_current_cgroup_id();
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struct cgroup *cgrp, *ancestor;
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cgrp = bpf_cgroup_from_id(cgrp_id);
124+
if (!cgrp)
125+
return 0;
126+
127+
ancestor = bpf_cgroup_ancestor(cgrp, 1);
128+
if (!ancestor)
129+
goto out;
130+
131+
read_xattr(cgrp);
132+
bpf_cgroup_release(ancestor);
133+
out:
134+
bpf_cgroup_release(cgrp);
135+
return 0;
136+
}
137+
138+
SEC("cgroup/sendmsg4")
139+
__success
140+
int BPF_PROG(cgroup_skb)
141+
{
142+
u64 cgrp_id = bpf_get_current_cgroup_id();
143+
struct cgroup *cgrp, *ancestor;
144+
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cgrp = bpf_cgroup_from_id(cgrp_id);
146+
if (!cgrp)
147+
return 0;
148+
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ancestor = bpf_cgroup_ancestor(cgrp, 1);
150+
if (!ancestor)
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goto out;
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read_xattr(cgrp);
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bpf_cgroup_release(ancestor);
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out:
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bpf_cgroup_release(cgrp);
157+
return 0;
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}

‎tools/testing/selftests/bpf/progs/read_cgroupfs_xattr.c‎

Lines changed: 60 additions & 0 deletions
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@@ -0,0 +1,60 @@
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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
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#include <vmlinux.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_core_read.h>
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#include "bpf_experimental.h"
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char _license[] SEC("license") = "GPL";
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pid_t target_pid = 0;
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char xattr_value[64];
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static const char expected_value_a[] = "bpf_selftest_value_a";
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static const char expected_value_b[] = "bpf_selftest_value_b";
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bool found_value_a;
18+
bool found_value_b;
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20+
SEC("lsm.s/socket_connect")
21+
int BPF_PROG(test_socket_connect)
22+
{
23+
u64 cgrp_id = bpf_get_current_cgroup_id();
24+
struct cgroup_subsys_state *css, *tmp;
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struct bpf_dynptr value_ptr;
26+
struct cgroup *cgrp;
27+
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if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
29+
return 0;
30+
31+
bpf_rcu_read_lock();
32+
cgrp = bpf_cgroup_from_id(cgrp_id);
33+
if (!cgrp) {
34+
bpf_rcu_read_unlock();
35+
return 0;
36+
}
37+
38+
css = &cgrp->self;
39+
bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr);
40+
bpf_for_each(css, tmp, css, BPF_CGROUP_ITER_ANCESTORS_UP) {
41+
int ret;
42+
43+
ret = bpf_cgroup_read_xattr(tmp->cgroup, "user.bpf_test",
44+
&value_ptr);
45+
if (ret < 0)
46+
continue;
47+
48+
if (ret == sizeof(expected_value_a) &&
49+
!bpf_strncmp(xattr_value, sizeof(expected_value_a), expected_value_a))
50+
found_value_a = true;
51+
if (ret == sizeof(expected_value_b) &&
52+
!bpf_strncmp(xattr_value, sizeof(expected_value_b), expected_value_b))
53+
found_value_b = true;
54+
}
55+
56+
bpf_rcu_read_unlock();
57+
bpf_cgroup_release(cgrp);
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59+
return 0;
60+
}

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