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bpf: Update local storage test to check handling of null ptrs
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It was found in [1] that bpf_inode_storage_get helper did not check
the nullness of the passed owner ptr which caused an oops when
dereferenced. This change incorporates the example suggested in [1] into
the local storage selftest.

The test is updated to create a temporary directory instead of just
using a tempfile. In order to replicate the issue this copied rm binary
is renamed tiggering the inode_rename with a null pointer for the
new_inode. The logic to verify the setting and deletion of the inode
local storage of the old inode is also moved to this LSM hook.

The change also removes the copy_rm function and simply shells out
to copy files and recursively delete directories and consolidates the
logic of setting the initial inode storage to the bprm_committed_creds
hook and removes the file_open hook.

[1]: https://lore.kernel.org/bpf/CANaYP3HWkH91SN=wTNO9FL_2ztHfqcXKX38SSE-JJ2voh+vssw@mail.gmail.com

Suggested-by: Gilad Reti <gilad.reti@gmail.com>
Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210112075525.256820-2-kpsingh@kernel.org
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KP Singh authored and Daniel Borkmann committed Jan 12, 2021
1 parent 84d571d commit 2f94ac1
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Showing 2 changed files with 61 additions and 97 deletions.
96 changes: 26 additions & 70 deletions tools/testing/selftests/bpf/prog_tests/test_local_storage.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,61 +34,6 @@ struct storage {
struct bpf_spin_lock lock;
};

/* Copies an rm binary to a temp file. dest is a mkstemp template */
static int copy_rm(char *dest)
{
int fd_in, fd_out = -1, ret = 0;
struct stat stat;
char *buf = NULL;

fd_in = open("/bin/rm", O_RDONLY);
if (fd_in < 0)
return -errno;

fd_out = mkstemp(dest);
if (fd_out < 0) {
ret = -errno;
goto out;
}

ret = fstat(fd_in, &stat);
if (ret == -1) {
ret = -errno;
goto out;
}

buf = malloc(stat.st_blksize);
if (!buf) {
ret = -errno;
goto out;
}

while (ret = read(fd_in, buf, stat.st_blksize), ret > 0) {
ret = write(fd_out, buf, ret);
if (ret < 0) {
ret = -errno;
goto out;

}
}
if (ret < 0) {
ret = -errno;
goto out;

}

/* Set executable permission on the copied file */
ret = chmod(dest, 0100);
if (ret == -1)
ret = -errno;

out:
free(buf);
close(fd_in);
close(fd_out);
return ret;
}

/* Fork and exec the provided rm binary and return the exit code of the
* forked process and its pid.
*/
Expand Down Expand Up @@ -168,9 +113,11 @@ static bool check_syscall_operations(int map_fd, int obj_fd)

void test_test_local_storage(void)
{
char tmp_exec_path[PATH_MAX] = "/tmp/copy_of_rmXXXXXX";
char tmp_dir_path[64] = "/tmp/local_storageXXXXXX";
int err, serv_sk = -1, task_fd = -1, rm_fd = -1;
struct local_storage *skel = NULL;
char tmp_exec_path[64];
char cmd[256];

skel = local_storage__open_and_load();
if (CHECK(!skel, "skel_load", "lsm skeleton failed\n"))
Expand All @@ -189,18 +136,24 @@ void test_test_local_storage(void)
task_fd))
goto close_prog;

err = copy_rm(tmp_exec_path);
if (CHECK(err < 0, "copy_rm", "err %d errno %d\n", err, errno))
if (CHECK(!mkdtemp(tmp_dir_path), "mkdtemp",
"unable to create tmpdir: %d\n", errno))
goto close_prog;

snprintf(tmp_exec_path, sizeof(tmp_exec_path), "%s/copy_of_rm",
tmp_dir_path);
snprintf(cmd, sizeof(cmd), "cp /bin/rm %s", tmp_exec_path);
if (CHECK_FAIL(system(cmd)))
goto close_prog_rmdir;

rm_fd = open(tmp_exec_path, O_RDONLY);
if (CHECK(rm_fd < 0, "open", "failed to open %s err:%d, errno:%d",
tmp_exec_path, rm_fd, errno))
goto close_prog;
goto close_prog_rmdir;

if (!check_syscall_operations(bpf_map__fd(skel->maps.inode_storage_map),
rm_fd))
goto close_prog;
goto close_prog_rmdir;

/* Sets skel->bss->monitored_pid to the pid of the forked child
* forks a child process that executes tmp_exec_path and tries to
Expand All @@ -209,33 +162,36 @@ void test_test_local_storage(void)
*/
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_unlink;
goto close_prog_rmdir;

/* Set the process being monitored to be the current process */
skel->bss->monitored_pid = getpid();

/* 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_unlink;
/* Move copy_of_rm to a new location so that it triggers the
* inode_rename LSM hook with a new_dentry that has a NULL inode ptr.
*/
snprintf(cmd, sizeof(cmd), "mv %s/copy_of_rm %s/check_null_ptr",
tmp_dir_path, tmp_dir_path);
if (CHECK_FAIL(system(cmd)))
goto close_prog_rmdir;

CHECK(skel->data->inode_storage_result != 0, "inode_storage_result",
"inode_local_storage not set\n");

serv_sk = start_server(AF_INET6, SOCK_STREAM, NULL, 0, 0);
if (CHECK(serv_sk < 0, "start_server", "failed to start server\n"))
goto close_prog;
goto close_prog_rmdir;

CHECK(skel->data->sk_storage_result != 0, "sk_storage_result",
"sk_local_storage not set\n");

if (!check_syscall_operations(bpf_map__fd(skel->maps.sk_storage_map),
serv_sk))
goto close_prog;
goto close_prog_rmdir;

close_prog_unlink:
unlink(tmp_exec_path);
close_prog_rmdir:
snprintf(cmd, sizeof(cmd), "rm -rf %s", tmp_dir_path);
system(cmd);
close_prog:
close(serv_sk);
close(rm_fd);
Expand Down
62 changes: 35 additions & 27 deletions tools/testing/selftests/bpf/progs/local_storage.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,6 @@ int BPF_PROG(unlink_hook, struct inode *dir, struct dentry *victim)
__u32 pid = bpf_get_current_pid_tgid() >> 32;
struct local_storage *storage;
bool is_self_unlink;
int err;

if (pid != monitored_pid)
return 0;
Expand All @@ -66,8 +65,27 @@ int BPF_PROG(unlink_hook, struct inode *dir, struct dentry *victim)
return -EPERM;
}

storage = bpf_inode_storage_get(&inode_storage_map, victim->d_inode, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
return 0;
}

SEC("lsm/inode_rename")
int BPF_PROG(inode_rename, struct inode *old_dir, struct dentry *old_dentry,
struct inode *new_dir, struct dentry *new_dentry,
unsigned int flags)
{
__u32 pid = bpf_get_current_pid_tgid() >> 32;
struct local_storage *storage;
int err;

/* new_dentry->d_inode can be NULL when the inode is renamed to a file
* that did not exist before. The helper should be able to handle this
* NULL pointer.
*/
bpf_inode_storage_get(&inode_storage_map, new_dentry->d_inode, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);

storage = bpf_inode_storage_get(&inode_storage_map, old_dentry->d_inode,
0, 0);
if (!storage)
return 0;

Expand All @@ -76,7 +94,7 @@ int BPF_PROG(unlink_hook, struct inode *dir, struct dentry *victim)
inode_storage_result = -1;
bpf_spin_unlock(&storage->lock);

err = bpf_inode_storage_delete(&inode_storage_map, victim->d_inode);
err = bpf_inode_storage_delete(&inode_storage_map, old_dentry->d_inode);
if (!err)
inode_storage_result = err;

Expand Down Expand Up @@ -133,37 +151,18 @@ int BPF_PROG(socket_post_create, struct socket *sock, int family, int type,
return 0;
}

SEC("lsm/file_open")
int BPF_PROG(file_open, struct file *file)
{
__u32 pid = bpf_get_current_pid_tgid() >> 32;
struct local_storage *storage;

if (pid != monitored_pid)
return 0;

if (!file->f_inode)
return 0;

storage = bpf_inode_storage_get(&inode_storage_map, file->f_inode, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
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)
{
__u32 pid = bpf_get_current_pid_tgid() >> 32;
struct local_storage *storage;

if (pid != monitored_pid)
return;

storage = bpf_task_storage_get(&task_storage_map,
bpf_get_current_task_btf(), 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
Expand All @@ -172,4 +171,13 @@ void BPF_PROG(exec, struct linux_binprm *bprm)
storage->exec_inode = bprm->file->f_inode;
bpf_spin_unlock(&storage->lock);
}

storage = bpf_inode_storage_get(&inode_storage_map, bprm->file->f_inode,
0, BPF_LOCAL_STORAGE_GET_F_CREATE);
if (!storage)
return;

bpf_spin_lock(&storage->lock);
storage->value = DUMMY_STORAGE_VALUE;
bpf_spin_unlock(&storage->lock);
}

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