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Message-Id: <d8af908f00b77415caa3eb0f4de631c3794e4909.1725494372.git.fahimitahera@gmail.com>
Date: Wed, 4 Sep 2024 18:14:01 -0600
From: Tahera Fahimi <fahimitahera@...il.com>
To: outreachy@...ts.linux.dev
Cc: mic@...ikod.net,
gnoack@...gle.com,
paul@...l-moore.com,
jmorris@...ei.org,
serge@...lyn.com,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org,
bjorn3_gh@...tonmail.com,
jannh@...gle.com,
netdev@...r.kernel.org,
Tahera Fahimi <fahimitahera@...il.com>
Subject: [PATCH v11 7/8] sample/landlock: Add support abstract UNIX socket restriction
A sandboxer can receive the character "a" as input from the environment
variable LL_SCOPE to restrict the abstract UNIX sockets from connecting
to a process outside its scoped domain.
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 with
command "socat - abstract-connect:mysocket", the connection will fail.
Signed-off-by: Tahera Fahimi <fahimitahera@...il.com>
---
v11:
- Change implementation of check_ruleset_scope function to make it less
bug prone.
- Imptovement on the commit description.
v10:
- Minor improvement in code based on v9.
v9:
- Add a restrict approach on input of LL_SCOPED, so it only allows zero
or one "a" to be the input.
v8:
- Adding check_ruleset_scope function to parse the scope environment
variable and update the landlock attribute based on the restriction
provided by the user.
- Adding Mickaël Salaün reviews on version 7.
v7:
- Adding IPC scoping to the sandbox demo by defining a new "LL_SCOPED"
environment variable. "LL_SCOPED" gets value "a" to restrict abstract
unix sockets.
- Change LANDLOCK_ABI_LAST to 6.
---
samples/landlock/sandboxer.c | 61 +++++++++++++++++++++++++++++++++---
1 file changed, 57 insertions(+), 4 deletions(-)
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index e8223c3e781a..18d072c23a23 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -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 +187,45 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
return ret;
}
+static bool check_ruleset_scope(const char *const env_var,
+ struct landlock_ruleset_attr *ruleset_attr)
+{
+ bool abstract_scoping = false;
+ bool ret = true;
+ char *env_type_scope, *env_type_scope_next, *ipc_scoping_name;
+
+ /* scoping is not supported by Landlock ABI */
+ if (!(ruleset_attr->scoped & LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET))
+ return ret;
+
+ env_type_scope = getenv(env_var);
+ /* scoping is not supported by the user */
+ if (!env_type_scope || strcmp("", env_type_scope) == 0) {
+ ruleset_attr->scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
+ return ret;
+ }
+
+ env_type_scope = strdup(env_type_scope);
+ unsetenv(env_var);
+ 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, "Unsupported scoping \"%s\"\n",
+ ipc_scoping_name);
+ ret = false;
+ goto out_free_name;
+ }
+ }
+ if (!abstract_scoping)
+ ruleset_attr->scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
+out_free_name:
+ free(env_type_scope);
+ return ret;
+}
+
/* clang-format off */
#define ACCESS_FS_ROUGHLY_READ ( \
@@ -208,7 +250,7 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
/* 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 +265,15 @@ 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_SCOPED_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 +294,18 @@ 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 restrictions on 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 +373,10 @@ 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_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */
+ ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
fprintf(stderr,
"Hint: You should update the running kernel "
"to leverage Landlock features "
@@ -358,6 +408,9 @@ 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) {
--
2.34.1
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