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.
Signed-off-by: Song Liu <song@kernel.org>
---
.../selftests/bpf/prog_tests/cgroup_xattr.c | 145 ++++++++++++++++++
.../selftests/bpf/progs/cgroup_read_xattr.c | 136 ++++++++++++++++
.../selftests/bpf/progs/read_cgroupfs_xattr.c | 60 ++++++++
3 files changed, 341 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c
create mode 100644 tools/testing/selftests/bpf/progs/cgroup_read_xattr.c
create mode 100644 tools/testing/selftests/bpf/progs/read_cgroupfs_xattr.c
diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c b/tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c
new file mode 100644
index 000000000000..87978a0f7eb7
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_xattr.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/xattr.h>
+
+#include <test_progs.h>
+
+#include "read_cgroupfs_xattr.skel.h"
+#include "cgroup_read_xattr.skel.h"
+
+#define CGROUP_FS_ROOT "/sys/fs/cgroup/"
+#define CGROUP_FS_PARENT CGROUP_FS_ROOT "foo/"
+#define CGROUP_FS_CHILD CGROUP_FS_PARENT "bar/"
+
+static int move_pid_to_cgroup(const char *cgroup_folder, pid_t pid)
+{
+ char filename[128];
+ char pid_str[64];
+ int procs_fd;
+ int ret;
+
+ snprintf(filename, sizeof(filename), "%scgroup.procs", cgroup_folder);
+ snprintf(pid_str, sizeof(pid_str), "%d", pid);
+
+ procs_fd = open(filename, O_WRONLY | O_APPEND);
+ if (!ASSERT_OK_FD(procs_fd, "open"))
+ return -1;
+
+ ret = write(procs_fd, pid_str, strlen(pid_str));
+ close(procs_fd);
+ if (!ASSERT_GT(ret, 0, "write cgroup.procs"))
+ return -1;
+ return 0;
+}
+
+static void reset_cgroups_and_lo(void)
+{
+ rmdir(CGROUP_FS_CHILD);
+ rmdir(CGROUP_FS_PARENT);
+ system("ip addr del 1.1.1.1/32 dev lo");
+ system("ip link set dev lo down");
+}
+
+static const char xattr_value_a[] = "bpf_selftest_value_a";
+static const char xattr_value_b[] = "bpf_selftest_value_b";
+static const char xattr_name[] = "user.bpf_test";
+
+static int setup_cgroups_and_lo(void)
+{
+ int err;
+
+ err = mkdir(CGROUP_FS_PARENT, 0755);
+ if (!ASSERT_OK(err, "mkdir 1"))
+ goto error;
+ err = mkdir(CGROUP_FS_CHILD, 0755);
+ if (!ASSERT_OK(err, "mkdir 2"))
+ goto error;
+
+ err = setxattr(CGROUP_FS_PARENT, xattr_name, xattr_value_a,
+ strlen(xattr_value_a) + 1, 0);
+ if (!ASSERT_OK(err, "setxattr 1"))
+ goto error;
+
+ err = setxattr(CGROUP_FS_CHILD, xattr_name, xattr_value_b,
+ strlen(xattr_value_b) + 1, 0);
+ if (!ASSERT_OK(err, "setxattr 2"))
+ goto error;
+
+ err = system("ip link set dev lo up");
+ if (!ASSERT_OK(err, "lo up"))
+ goto error;
+
+ err = system("ip addr add 1.1.1.1 dev lo");
+ if (!ASSERT_OK(err, "lo addr v4"))
+ goto error;
+
+ err = write_sysctl("/proc/sys/net/ipv4/ping_group_range", "0 0");
+ if (!ASSERT_OK(err, "write_sysctl"))
+ goto error;
+
+ return 0;
+error:
+ reset_cgroups_and_lo();
+ return err;
+}
+
+static void test_read_cgroup_xattr(void)
+{
+ struct sockaddr_in sa4 = {
+ .sin_family = AF_INET,
+ .sin_addr.s_addr = htonl(INADDR_LOOPBACK),
+ };
+ struct read_cgroupfs_xattr *skel = NULL;
+ pid_t pid = gettid();
+ int sock_fd = -1;
+ int connect_fd = -1;
+
+ if (!ASSERT_OK(setup_cgroups_and_lo(), "setup_cgroups_and_lo"))
+ return;
+ if (!ASSERT_OK(move_pid_to_cgroup(CGROUP_FS_CHILD, pid),
+ "move_pid_to_cgroup"))
+ goto out;
+
+ skel = read_cgroupfs_xattr__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "read_cgroupfs_xattr__open_and_load"))
+ goto out;
+
+ skel->bss->target_pid = pid;
+
+ if (!ASSERT_OK(read_cgroupfs_xattr__attach(skel), "read_cgroupfs_xattr__attach"))
+ goto out;
+
+ sock_fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP);
+ if (!ASSERT_OK_FD(sock_fd, "sock create"))
+ goto out;
+
+ connect_fd = connect(sock_fd, &sa4, sizeof(sa4));
+ if (!ASSERT_OK_FD(connect_fd, "connect 1"))
+ goto out;
+ close(connect_fd);
+
+ ASSERT_TRUE(skel->bss->found_value_a, "found_value_a");
+ ASSERT_TRUE(skel->bss->found_value_b, "found_value_b");
+
+out:
+ close(connect_fd);
+ close(sock_fd);
+ read_cgroupfs_xattr__destroy(skel);
+ move_pid_to_cgroup(CGROUP_FS_ROOT, pid);
+ reset_cgroups_and_lo();
+}
+
+void test_cgroup_xattr(void)
+{
+ RUN_TESTS(cgroup_read_xattr);
+
+ if (test__start_subtest("read_cgroupfs_xattr"))
+ test_read_cgroup_xattr();
+}
diff --git a/tools/testing/selftests/bpf/progs/cgroup_read_xattr.c b/tools/testing/selftests/bpf/progs/cgroup_read_xattr.c
new file mode 100644
index 000000000000..b50ccb3aebcf
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/cgroup_read_xattr.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include "bpf_experimental.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+char value[16];
+
+__always_inline void read_xattr(struct cgroup *cgroup)
+{
+ struct bpf_dynptr value_ptr;
+
+ bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
+ bpf_cgroup_read_xattr(cgroup, "user.bpf_test",
+ &value_ptr);
+}
+
+SEC("lsm.s/socket_connect")
+__success
+int BPF_PROG(trusted_cgroup_ptr_sleepable)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup *cgrp;
+
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp)
+ return 0;
+
+ read_xattr(cgrp);
+ bpf_cgroup_release(cgrp);
+ return 0;
+}
+
+SEC("lsm/socket_connect")
+__success
+int BPF_PROG(trusted_cgroup_ptr_non_sleepable)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup *cgrp;
+
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp)
+ return 0;
+
+ read_xattr(cgrp);
+ bpf_cgroup_release(cgrp);
+ return 0;
+}
+
+SEC("lsm/socket_connect")
+__success
+int BPF_PROG(use_css_iter_non_sleepable)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup_subsys_state *css;
+ struct cgroup *cgrp;
+
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp)
+ return 0;
+
+ bpf_for_each(css, css, &cgrp->self, BPF_CGROUP_ITER_ANCESTORS_UP)
+ read_xattr(css->cgroup);
+
+ bpf_cgroup_release(cgrp);
+ return 0;
+}
+
+SEC("lsm.s/socket_connect")
+__failure __msg("expected an RCU CS")
+int BPF_PROG(use_css_iter_sleepable_missing_rcu_lock)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup_subsys_state *css;
+ struct cgroup *cgrp;
+
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp)
+ return 0;
+
+ bpf_for_each(css, css, &cgrp->self, BPF_CGROUP_ITER_ANCESTORS_UP)
+ read_xattr(css->cgroup);
+
+ bpf_cgroup_release(cgrp);
+ return 0;
+}
+
+SEC("lsm.s/socket_connect")
+__success
+int BPF_PROG(use_css_iter_sleepable_with_rcu_lock)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup_subsys_state *css;
+ struct cgroup *cgrp;
+
+ bpf_rcu_read_lock();
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp)
+ goto out;
+
+ bpf_for_each(css, css, &cgrp->self, BPF_CGROUP_ITER_ANCESTORS_UP)
+ read_xattr(css->cgroup);
+
+ bpf_cgroup_release(cgrp);
+out:
+ bpf_rcu_read_unlock();
+ return 0;
+}
+
+SEC("lsm/socket_connect")
+__success
+int BPF_PROG(use_bpf_cgroup_ancestor)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup *cgrp, *ancestor;
+
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp)
+ return 0;
+
+ ancestor = bpf_cgroup_ancestor(cgrp, 1);
+ if (!ancestor)
+ goto out;
+
+ read_xattr(cgrp);
+ bpf_cgroup_release(ancestor);
+out:
+ bpf_cgroup_release(cgrp);
+ return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/read_cgroupfs_xattr.c b/tools/testing/selftests/bpf/progs/read_cgroupfs_xattr.c
new file mode 100644
index 000000000000..855f85fc5522
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/read_cgroupfs_xattr.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include "bpf_experimental.h"
+
+char _license[] SEC("license") = "GPL";
+
+pid_t target_pid = 0;
+
+char xattr_value[64];
+static const char expected_value_a[] = "bpf_selftest_value_a";
+static const char expected_value_b[] = "bpf_selftest_value_b";
+bool found_value_a;
+bool found_value_b;
+
+SEC("lsm.s/socket_connect")
+int BPF_PROG(test_socket_connect)
+{
+ u64 cgrp_id = bpf_get_current_cgroup_id();
+ struct cgroup_subsys_state *css, *tmp;
+ struct bpf_dynptr value_ptr;
+ struct cgroup *cgrp;
+
+ if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
+ return 0;
+
+ bpf_rcu_read_lock();
+ cgrp = bpf_cgroup_from_id(cgrp_id);
+ if (!cgrp) {
+ bpf_rcu_read_unlock();
+ return 0;
+ }
+
+ css = &cgrp->self;
+ bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr);
+ bpf_for_each(css, tmp, css, BPF_CGROUP_ITER_ANCESTORS_UP) {
+ int ret;
+
+ ret = bpf_cgroup_read_xattr(tmp->cgroup, "user.bpf_test",
+ &value_ptr);
+ if (ret < 0)
+ continue;
+
+ if (ret == sizeof(expected_value_a) &&
+ !bpf_strncmp(xattr_value, sizeof(expected_value_a), expected_value_a))
+ found_value_a = true;
+ if (ret == sizeof(expected_value_b) &&
+ !bpf_strncmp(xattr_value, sizeof(expected_value_b), expected_value_b))
+ found_value_b = true;
+ }
+
+ bpf_rcu_read_unlock();
+ bpf_cgroup_release(cgrp);
+
+ return 0;
+}
--
2.47.1On Thu, Jun 19, 2025 at 3:02 PM Song Liu <song@kernel.org> wrote: > + bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr); https://github.com/kernel-patches/bpf/actions/runs/15767046528/job/44445539248 progs/cgroup_read_xattr.c:19:9: error: ‘bpf_dynptr_from_mem’ is static but used in inline function ‘read_xattr’ which is not static [-Werror] 19 | bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr); | ^~~~~~~~~~~~~~~~~~~ Jose, Could you please help us understand this gcc-bpf error ? What does it mean?
On Fri, 2025-06-20 at 11:11 -0700, Alexei Starovoitov wrote:
> On Thu, Jun 19, 2025 at 3:02 PM Song Liu <song@kernel.org> wrote:
> > + bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr);
>
> https://github.com/kernel-patches/bpf/actions/runs/15767046528/job/44445539248
>
> progs/cgroup_read_xattr.c:19:9: error: ‘bpf_dynptr_from_mem’ is static
> but used in inline function ‘read_xattr’ which is not static [-Werror]
> 19 | bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
> > ^~~~~~~~~~~~~~~~~~~
>
>
> Jose,
>
> Could you please help us understand this gcc-bpf error ?
> What does it mean?
Not Jose, but was curious.
Some googling lead to the following C99 wording [1]:
> An inline definition of a function with external linkage shall not
> contain a definition of a modifiable object with static storage
> duration, and shall not contain a reference to an identifier with
> internal linkage
[1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
6.7.4 Function specifiers, paragraph 3
The helper is defined as `static`:
static long (* const bpf_dynptr_from_mem)(...) = (void *) 197;
While `read_xattr` has external linkage:
__always_inline void read_xattr(struct cgroup *cgroup)
{
...
bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
...
}
I think that declaring `read_xattr` as `static` should help with gcc.
> On Fri, 2025-06-20 at 11:11 -0700, Alexei Starovoitov wrote:
>> On Thu, Jun 19, 2025 at 3:02 PM Song Liu <song@kernel.org> wrote:
>> > + bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr);
>>
>> https://github.com/kernel-patches/bpf/actions/runs/15767046528/job/44445539248
>>
>> progs/cgroup_read_xattr.c:19:9: error: ‘bpf_dynptr_from_mem’ is static
>> but used in inline function ‘read_xattr’ which is not static [-Werror]
>> 19 | bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
>> > ^~~~~~~~~~~~~~~~~~~
>>
>>
>> Jose,
>>
>> Could you please help us understand this gcc-bpf error ?
>> What does it mean?
>
> Not Jose, but was curious.
> Some googling lead to the following C99 wording [1]:
>
> > An inline definition of a function with external linkage shall not
> > contain a definition of a modifiable object with static storage
> > duration, and shall not contain a reference to an identifier with
> > internal linkage
>
> [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
> 6.7.4 Function specifiers, paragraph 3
>
> The helper is defined as `static`:
>
> static long (* const bpf_dynptr_from_mem)(...) = (void *) 197;
>
> While `read_xattr` has external linkage:
>
> __always_inline void read_xattr(struct cgroup *cgroup)
> {
> ...
> bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
> ...
> }
>
> I think that declaring `read_xattr` as `static` should help with gcc.
Yes I agree that is the issue. It is a restriction introduced by C99.
I wasn't aware of it so I had to look it up.
If you need read_xattr to be accessible from other compilation units and
inlinable, you may declare it as static inline and put it in a header
file. It will then use the copies of the helper pointers in the other
compilation units.
Alternatively, with GCC you could try to add a direct declaration for
the helper function to progs/cgroup_read_xattr.c, that doesnt need to
use any static intermediate pointer:
#if COMPILING_WITH_GCC
long _bpf_dynptr_from_mem (...) __attribute__ ((kernel_helper (197)));
#define bpf_dynptr_from_mem _bpf_dynptr_from_mem
#endif
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