From: KP Singh <kpsi...@google.com>
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 temporary file is cleaned up later in the test.
Signed-off-by: KP Singh <kpsi...@google.com>
---
.../bpf/prog_tests/test_local_storage.c | 89 ++++++++++++++++---
.../selftests/bpf/progs/local_storage.c | 44 +++++++--
2 files changed, 116 insertions(+), 17 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..0e41b27f3471 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 +4,83 @@
* 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)
+/* 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_in = open("/bin/rm", O_RDONLY);
+ if (fd_in < 0)
+ return fd_in;
+
+ fd_out = mkstemp(dest);
+ if (fd_out < 0)
+ return fd_out;
- fd = mkstemp(fname);
- if (fd < 0)
- return fd;
+ ret = fstat(fd_in, &stat);
+ if (ret == -1)
+ return errno;
- close(fd);
- unlink(fname);
+ 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;
+}
void test_test_local_storage(void)
{
struct local_storage *skel = NULL;
int err, duration = 0, serv_sk = -1;
+ char tmp_exec_path[PATH_MAX] = "/tmp/copy_of_rmXXXXXX";
skel = local_storage__open_and_load();
if (CHECK(!skel, "skel_load", "lsm skeleton failed\n"))
@@ -37,10 +90,26 @@ void test_test_local_storage(void)
if (CHECK(err, "attach", "lsm attach failed: %d\n", err))
goto close_prog;
+ err = copy_rm(tmp_exec_path);
+ if (CHECK(err < 0, "copy_executable", "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",
diff --git a/tools/testing/selftests/bpf/progs/local_storage.c
b/tools/testing/selftests/bpf/progs/local_storage.c
index 5acf9203a69a..eb280cd0c416 100644
--- a/tools/testing/selftests/bpf/progs/local_storage.c
+++ b/tools/testing/selftests/bpf/progs/local_storage.c
@@ -17,7 +17,8 @@ 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;
};
@@ -25,26 +26,40 @@ 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 | BPF_F_CLONE);
+ __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;
int err;
if (pid != monitored_pid)
return 0;
+ storage = bpf_task_storage_get(&task_storage_map,
+ bpf_get_current_task_btf(), 0, 0);
+
+ /* Don't let an executable delete itself */
+ if (storage && storage->exec_inode == victim->d_inode)
+ return -EPERM;
+
storage = bpf_inode_storage_get(&inode_storage_map, victim->d_inode, 0,
BPF_SK_STORAGE_GET_F_CREATE);
if (!storage)
@@ -65,7 +80,7 @@ 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)
@@ -91,7 +106,7 @@ 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;
@@ -110,7 +125,7 @@ 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;
@@ -126,3 +141,18 @@ int BPF_PROG(file_open, struct file *file)
storage->value = DUMMY_STORAGE_VALUE;
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)
+ storage->exec_inode = bprm->file->f_inode;
+}
--
2.29.0.rc2.309.g374f81d7ae-goog
