From: KP Singh <kpsi...@google.com>

The test exercises the syscall based map operations by creating a pidfd
for the current process.

For verifying kernel / LSM functionality, the test implements a simple
MAC policy which denies an executable from unlinking itself. The LSM
program bprm_committed_creds sets a task_local_storage with a pointer to
the inode. This is then used to detect if the task is trying to unlink
itself in the inode_unlink LSM hook.

The test copies /bin/rm to /tmp and executes it in a child thread with
the intention of deleting itself. A successful test should prevent the
the running executable from deleting itself.

The bpf programs are also updated to call bpf_spin_{lock, unlock} to
trigger the verfier checks for spin locks.

The temporary file is cleaned up later in the test.

Signed-off-by: KP Singh <kpsi...@google.com>
---
 .../bpf/prog_tests/test_local_storage.c       | 167 ++++++++++++++++--
 .../selftests/bpf/progs/local_storage.c       |  61 ++++++-
 2 files changed, 210 insertions(+), 18 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/test_local_storage.c 
b/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
index 91cd6f357246..feba23f8848b 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_local_storage.c
@@ -4,30 +4,149 @@
  * Copyright (C) 2020 Google LLC.
  */
 
+#define _GNU_SOURCE
+
+#include <asm-generic/errno-base.h>
+#include <unistd.h>
+#include <sys/stat.h>
 #include <test_progs.h>
 #include <linux/limits.h>
 
 #include "local_storage.skel.h"
 #include "network_helpers.h"
 
-int create_and_unlink_file(void)
+static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
+{
+       return syscall(__NR_pidfd_open, pid, flags);
+}
+
+unsigned int duration;
+
+#define TEST_STORAGE_VALUE 0xbeefdead
+
+struct storage {
+       void *inode;
+       unsigned int value;
+       /* Lock ensures that spin locked versions of local stoage operations
+        * also work, most operations in this tests are still single threaded
+        */
+       struct bpf_spin_lock lock;
+};
+
+/* Copies an rm binary to a temp file. dest is a mkstemp template */
+int copy_rm(char *dest)
 {
-       char fname[PATH_MAX] = "/tmp/fileXXXXXX";
-       int fd;
+       int ret, fd_in, fd_out;
+       struct stat stat;
 
-       fd = mkstemp(fname);
-       if (fd < 0)
-               return fd;
+       fd_in = open("/bin/rm", O_RDONLY);
+       if (fd_in < 0)
+               return fd_in;
 
-       close(fd);
-       unlink(fname);
+       fd_out = mkstemp(dest);
+       if (fd_out < 0)
+               return fd_out;
+
+       ret = fstat(fd_in, &stat);
+       if (ret == -1)
+               return errno;
+
+       ret = copy_file_range(fd_in, NULL, fd_out, NULL, stat.st_size, 0);
+       if (ret == -1)
+               return errno;
+
+       /* Set executable permission on the copied file */
+       ret = chmod(dest, 0100);
+       if (ret == -1)
+               return errno;
+
+       close(fd_in);
+       close(fd_out);
        return 0;
 }
 
+/* Fork and exec the provided rm binary and return the exit code of the
+ * forked process and its pid.
+ */
+int run_self_unlink(int *monitored_pid, const char *rm_path)
+{
+       int child_pid, child_status, ret;
+       int null_fd;
+
+       child_pid = fork();
+       if (child_pid == 0) {
+               null_fd = open("/dev/null", O_WRONLY);
+               dup2(null_fd, STDOUT_FILENO);
+               dup2(null_fd, STDERR_FILENO);
+               close(null_fd);
+
+               *monitored_pid = getpid();
+               /* Use the copied /usr/bin/rm to delete itself
+                * /tmp/copy_of_rm /tmp/copy_of_rm.
+                */
+               ret = execlp(rm_path, rm_path, rm_path, NULL);
+               if (ret)
+                       exit(errno);
+       } else if (child_pid > 0) {
+               waitpid(child_pid, &child_status, 0);
+               return WEXITSTATUS(child_status);
+       }
+
+       return -EINVAL;
+}
+
+bool check_syscall_operations(int map_fd, int obj_fd)
+{
+       struct storage val = { .value = TEST_STORAGE_VALUE, .lock = { 0 } },
+                      lookup_val = { .value = 0, .lock = { 0 } };
+       int err;
+
+       /* Looking up an existing element should fail initially */
+       err = bpf_map_lookup_elem_flags(map_fd, &obj_fd, &lookup_val,
+                                       BPF_F_LOCK);
+       if (CHECK(!err || errno != ENOENT, "bpf_map_lookup_elem",
+                 "err:%d errno:%d\n", err, errno))
+               return false;
+
+       /* Create a new element */
+       err = bpf_map_update_elem(map_fd, &obj_fd, &val,
+                                 BPF_NOEXIST | BPF_F_LOCK);
+       if (CHECK(err < 0, "bpf_map_update_elem", "err:%d errno:%d\n", err,
+                 errno))
+               return false;
+
+       /* Lookup the newly created element */
+       err = bpf_map_lookup_elem_flags(map_fd, &obj_fd, &lookup_val,
+                                       BPF_F_LOCK);
+       if (CHECK(err < 0, "bpf_map_lookup_elem", "err:%d errno:%d", err,
+                 errno))
+               return false;
+
+       /* Check the value of the newly created element */
+       if (CHECK(lookup_val.value != val.value, "bpf_map_lookup_elem",
+                 "value got = %x errno:%d", lookup_val.value, val.value))
+               return false;
+
+       err = bpf_map_delete_elem(map_fd, &obj_fd);
+       if (CHECK(err, "bpf_map_delete_elem()", "err:%d errno:%d\n", err,
+                 errno))
+               return false;
+
+       /* The lookup should fail, now that the element has been deleted */
+       err = bpf_map_lookup_elem_flags(map_fd, &obj_fd, &lookup_val,
+                                       BPF_F_LOCK);
+       if (CHECK(!err || errno != ENOENT, "bpf_map_lookup_elem",
+                 "err:%d errno:%d\n", err, errno))
+               return false;
+
+       return true;
+}
+
 void test_test_local_storage(void)
 {
+       char tmp_exec_path[PATH_MAX] = "/tmp/copy_of_rmXXXXXX";
+       int err, serv_sk = -1, task_fd = -1;
        struct local_storage *skel = NULL;
-       int err, duration = 0, serv_sk = -1;
 
        skel = local_storage__open_and_load();
        if (CHECK(!skel, "skel_load", "lsm skeleton failed\n"))
@@ -37,10 +156,35 @@ void test_test_local_storage(void)
        if (CHECK(err, "attach", "lsm attach failed: %d\n", err))
                goto close_prog;
 
+       task_fd = sys_pidfd_open(getpid(), 0);
+       if (CHECK(task_fd < 0, "pidfd_open",
+                 "failed to get pidfd err:%d, errno:%d", task_fd, errno))
+               goto close_prog;
+
+       if (!check_syscall_operations(bpf_map__fd(skel->maps.task_storage_map),
+                                     task_fd))
+               goto close_prog;
+
+       err = copy_rm(tmp_exec_path);
+       if (CHECK(err < 0, "copy_rm", "err %d errno %d\n", err, errno))
+               goto close_prog;
+
+       /* Sets skel->bss->monitored_pid to the pid of the forked child
+        * forks a child process that executes tmp_exec_path and tries to
+        * unlink its executable. This operation should be denied by the loaded
+        * LSM program.
+        */
+       err = run_self_unlink(&skel->bss->monitored_pid, tmp_exec_path);
+       if (CHECK(err != EPERM, "run_self_unlink", "err %d want EPERM\n", err))
+               goto close_prog;
+
+       /* Set the process being monitored to be the current process */
        skel->bss->monitored_pid = getpid();
 
-       err = create_and_unlink_file();
-       if (CHECK(err < 0, "exec_cmd", "err %d errno %d\n", err, errno))
+       /* Remove the temporary created executable */
+       err = unlink(tmp_exec_path);
+       if (CHECK(err != 0, "unlink", "unable to unlink %s: %d", tmp_exec_path,
+                 errno))
                goto close_prog;
 
        CHECK(skel->data->inode_storage_result != 0, "inode_storage_result",
@@ -56,5 +200,6 @@ void test_test_local_storage(void)
        close(serv_sk);
 
 close_prog:
+       close(task_fd);
        local_storage__destroy(skel);
 }
diff --git a/tools/testing/selftests/bpf/progs/local_storage.c 
b/tools/testing/selftests/bpf/progs/local_storage.c
index ef3822bc7542..3e3de130f28f 100644
--- a/tools/testing/selftests/bpf/progs/local_storage.c
+++ b/tools/testing/selftests/bpf/progs/local_storage.c
@@ -17,41 +17,64 @@ int monitored_pid = 0;
 int inode_storage_result = -1;
 int sk_storage_result = -1;
 
-struct dummy_storage {
+struct local_storage {
+       struct inode *exec_inode;
        __u32 value;
+       struct bpf_spin_lock lock;
 };
 
 struct {
        __uint(type, BPF_MAP_TYPE_INODE_STORAGE);
        __uint(map_flags, BPF_F_NO_PREALLOC);
        __type(key, int);
-       __type(value, struct dummy_storage);
+       __type(value, struct local_storage);
 } inode_storage_map SEC(".maps");
 
 struct {
        __uint(type, BPF_MAP_TYPE_SK_STORAGE);
        __uint(map_flags, BPF_F_NO_PREALLOC | BPF_F_CLONE);
        __type(key, int);
-       __type(value, struct dummy_storage);
+       __type(value, struct local_storage);
 } sk_storage_map SEC(".maps");
 
+struct {
+       __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+       __uint(map_flags, BPF_F_NO_PREALLOC);
+       __type(key, int);
+       __type(value, struct local_storage);
+} task_storage_map SEC(".maps");
+
 SEC("lsm/inode_unlink")
 int BPF_PROG(unlink_hook, struct inode *dir, struct dentry *victim)
 {
        __u32 pid = bpf_get_current_pid_tgid() >> 32;
-       struct dummy_storage *storage;
+       struct local_storage *storage;
+       bool is_self_unlink;
        int err;
 
        if (pid != monitored_pid)
                return 0;
 
+       storage = bpf_task_storage_get(&task_storage_map,
+                                      bpf_get_current_task_btf(), 0, 0);
+       if (storage) {
+               /* Don't let an executable delete itself */
+               bpf_spin_lock(&storage->lock);
+               is_self_unlink = storage->exec_inode == victim->d_inode;
+               bpf_spin_unlock(&storage->lock);
+               if (is_self_unlink)
+                       return -EPERM;
+       }
+
        storage = bpf_inode_storage_get(&inode_storage_map, victim->d_inode, 0,
                                        BPF_LOCAL_STORAGE_GET_F_CREATE);
        if (!storage)
                return 0;
 
+       bpf_spin_lock(&storage->lock);
        if (storage->value != DUMMY_STORAGE_VALUE)
                inode_storage_result = -1;
+       bpf_spin_unlock(&storage->lock);
 
        err = bpf_inode_storage_delete(&inode_storage_map, victim->d_inode);
        if (!err)
@@ -65,7 +88,7 @@ int BPF_PROG(socket_bind, struct socket *sock, struct 
sockaddr *address,
             int addrlen)
 {
        __u32 pid = bpf_get_current_pid_tgid() >> 32;
-       struct dummy_storage *storage;
+       struct local_storage *storage;
        int err;
 
        if (pid != monitored_pid)
@@ -76,8 +99,10 @@ int BPF_PROG(socket_bind, struct socket *sock, struct 
sockaddr *address,
        if (!storage)
                return 0;
 
+       bpf_spin_lock(&storage->lock);
        if (storage->value != DUMMY_STORAGE_VALUE)
                sk_storage_result = -1;
+       bpf_spin_unlock(&storage->lock);
 
        err = bpf_sk_storage_delete(&sk_storage_map, sock->sk);
        if (!err)
@@ -91,7 +116,7 @@ int BPF_PROG(socket_post_create, struct socket *sock, int 
family, int type,
             int protocol, int kern)
 {
        __u32 pid = bpf_get_current_pid_tgid() >> 32;
-       struct dummy_storage *storage;
+       struct local_storage *storage;
 
        if (pid != monitored_pid)
                return 0;
@@ -101,7 +126,9 @@ int BPF_PROG(socket_post_create, struct socket *sock, int 
family, int type,
        if (!storage)
                return 0;
 
+       bpf_spin_lock(&storage->lock);
        storage->value = DUMMY_STORAGE_VALUE;
+       bpf_spin_unlock(&storage->lock);
 
        return 0;
 }
@@ -110,7 +137,7 @@ SEC("lsm/file_open")
 int BPF_PROG(file_open, struct file *file)
 {
        __u32 pid = bpf_get_current_pid_tgid() >> 32;
-       struct dummy_storage *storage;
+       struct local_storage *storage;
 
        if (pid != monitored_pid)
                return 0;
@@ -123,6 +150,26 @@ int BPF_PROG(file_open, struct file *file)
        if (!storage)
                return 0;
 
+       bpf_spin_lock(&storage->lock);
        storage->value = DUMMY_STORAGE_VALUE;
+       bpf_spin_unlock(&storage->lock);
        return 0;
 }
+
+/* This uses the local storage to remember the inode of the binary that a
+ * process was originally executing.
+ */
+SEC("lsm/bprm_committed_creds")
+void BPF_PROG(exec, struct linux_binprm *bprm)
+{
+       struct local_storage *storage;
+
+       storage = bpf_task_storage_get(&task_storage_map,
+                                      bpf_get_current_task_btf(), 0,
+                                      BPF_LOCAL_STORAGE_GET_F_CREATE);
+       if (storage) {
+               bpf_spin_lock(&storage->lock);
+               storage->exec_inode = bprm->file->f_inode;
+               bpf_spin_unlock(&storage->lock);
+       }
+}
-- 
2.29.1.341.ge80a0c044ae-goog

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