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samples/landlock: Add support for abstract UNIX socket scoping

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The sandboxer can receive the character "a" as input from the
environment variable LL_SCOPE to restrict sandboxed processes from
connecting to an abstract UNIX socket created by a process outside of
the sandbox.

Example
=======

Create an abstract UNIX socket to listen with socat(1):
  socat abstract-listen:mysocket -

Create a sandboxed shell and pass the character "a" to LL_SCOPED:
  LL_FS_RO=/ LL_FS_RW=. LL_SCOPED="a" ./sandboxer /bin/bash

Note that any other form of input (e.g. "a:a", "aa", etc) is not
acceptable.

If the sandboxed process tries to connect to the listening socket, the
connection will fail:
  socat - abstract-connect:mysocket

Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/d8af908f00b77415caa3eb0f4de631c3794e4909.1725494372.git.fahimitahera@gmail.com
[mic: Improve commit message, simplify check_ruleset_scope() with
inverted error code and only one scoped change, always unset environment
variable]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
This commit is contained in:
Tahera Fahimi 2024-09-04 18:14:01 -06:00 committed by Mickaël Salaün
parent 644a728506
commit 369b48b43a
No known key found for this signature in database
GPG Key ID: E5E3D0E88C82F6D2
1 changed files with 60 additions and 4 deletions
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64
samples/landlock/sandboxer.c
View File

@ -14,6 +14,7 @@
#include <fcntl.h>
#include <linux/landlock.h>
#include <linux/prctl.h>
#include <linux/socket.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
@ -22,6 +23,7 @@
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <stdbool.h>
#ifndef landlock_create_ruleset
static inline int
@ -55,6 +57,7 @@ static inline int landlock_restrict_self(const int ruleset_fd,
#define ENV_FS_RW_NAME "LL_FS_RW"
#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
#define ENV_SCOPED_NAME "LL_SCOPED"
#define ENV_DELIMITER ":"
static int parse_path(char *env_path, const char ***const path_list)
@ -184,6 +187,48 @@ out_free_name:
return ret;
}
/* Returns true on error, false otherwise. */
static bool check_ruleset_scope(const char *const env_var,
struct landlock_ruleset_attr *ruleset_attr)
{
char *env_type_scope, *env_type_scope_next, *ipc_scoping_name;
bool error = false;
bool abstract_scoping = false;
/* Scoping is not supported by Landlock ABI */
if (!(ruleset_attr->scoped & LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET))
goto out_unset;
env_type_scope = getenv(env_var);
/* Scoping is not supported by the user */
if (!env_type_scope || strcmp("", env_type_scope) == 0)
goto out_unset;
env_type_scope = strdup(env_type_scope);
env_type_scope_next = env_type_scope;
while ((ipc_scoping_name =
strsep(&env_type_scope_next, ENV_DELIMITER))) {
if (strcmp("a", ipc_scoping_name) == 0 && !abstract_scoping) {
abstract_scoping = true;
} else {
fprintf(stderr, "Unknown or duplicate scope \"%s\"\n",
ipc_scoping_name);
error = true;
goto out_free_name;
}
}
out_free_name:
free(env_type_scope);
out_unset:
if (!abstract_scoping)
ruleset_attr->scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
unsetenv(env_var);
return error;
}
/* clang-format off */
#define ACCESS_FS_ROUGHLY_READ ( \
@ -208,7 +253,7 @@ out_free_name:
/* clang-format on */
#define LANDLOCK_ABI_LAST 5
#define LANDLOCK_ABI_LAST 6
int main(const int argc, char *const argv[], char *const *const envp)
{
@ -223,14 +268,15 @@ int main(const int argc, char *const argv[], char *const *const envp)
.handled_access_fs = access_fs_rw,
.handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
LANDLOCK_ACCESS_NET_CONNECT_TCP,
.scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET,
};
if (argc < 2) {
fprintf(stderr,
"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s "
"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s "
"<cmd> [args]...\n\n",
ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
ENV_TCP_CONNECT_NAME, argv[0]);
ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]);
fprintf(stderr,
"Execute a command in a restricted environment.\n\n");
fprintf(stderr,
@ -251,15 +297,18 @@ int main(const int argc, char *const argv[], char *const *const envp)
fprintf(stderr,
"* %s: list of ports allowed to connect (client).\n",
ENV_TCP_CONNECT_NAME);
fprintf(stderr, "* %s: list of scoped IPCs.\n",
ENV_SCOPED_NAME);
fprintf(stderr,
"\nexample:\n"
"%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
"%s=\"9418\" "
"%s=\"80:443\" "
"%s=\"a\" "
"%s bash -i\n\n",
ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
ENV_TCP_CONNECT_NAME, argv[0]);
ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]);
fprintf(stderr,
"This sandboxer can use Landlock features "
"up to ABI version %d.\n",
@ -327,6 +376,10 @@ int main(const int argc, char *const argv[], char *const *const envp)
/* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
__attribute__((fallthrough));
case 5:
/* Removes LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET for ABI < 6 */
ruleset_attr.scoped &= ~LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
fprintf(stderr,
"Hint: You should update the running kernel "
"to leverage Landlock features "
@ -358,6 +411,9 @@ int main(const int argc, char *const argv[], char *const *const envp)
~LANDLOCK_ACCESS_NET_CONNECT_TCP;
}
if (check_ruleset_scope(ENV_SCOPED_NAME, &ruleset_attr))
return 1;
ruleset_fd =
landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
if (ruleset_fd < 0) {