[PATCH v3 5/6] sample/Landlock: Support signal scoping restriction

[Tahera Fahimi]

A sandboxer can receive the character "s" as input from the environment
variable LL_SCOPE to restrict itself from sending a signal to a process
outside its scoped domain.

Example
=======
Create a sandboxed shell and pass the character "s" to LL_SCOPED:
LL_FS_RO=/ LL_FS_RW=. LL_SCOPED="s" ./sandboxer /bin/bash
Try to send a SIGTRAP to a process with process ID <PID> through:
kill -SIGTRAP <PID>
The sandboxed process should not be able to send the signal.

Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>
---
v3:
- Add a restrict approach on input of LL_SCOPED, so it only allows
  zero or one "s" to be the input.
---
 samples/landlock/sandboxer.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index bec201eb96f7..32fec6cede2c 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -191,10 +191,12 @@ static bool check_ruleset_scope(const char *const env_var,
 				struct landlock_ruleset_attr *ruleset_attr)
 {
 	bool abstract_scoping = false;
+	bool signal_scoping = false;
 	bool ret = true;
 	char *env_type_scope, *env_type_scope_next, *ipc_scoping_name;
 
-	ruleset_attr->scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
+	ruleset_attr->scoped &= ~(LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET |
+				  LANDLOCK_SCOPED_SIGNAL);
 	env_type_scope = getenv(env_var);
 	/* scoping is not supported by the user */
 	if (!env_type_scope)
@@ -209,6 +211,10 @@ static bool check_ruleset_scope(const char *const env_var,
 			abstract_scoping = true;
 			ruleset_attr->scoped |=
 				LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
+		} else if (strcmp("s", ipc_scoping_name) == 0 &&
+			   !signal_scoping) {
+			signal_scoping = true;
+			ruleset_attr->scoped |= LANDLOCK_SCOPED_SIGNAL;
 		} else {
 			fprintf(stderr, "Unsupported scoping \"%s\"\n",
 				ipc_scoping_name);
@@ -260,7 +266,8 @@ 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,
+		.scoped = LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET |
+			  LANDLOCK_SCOPED_SIGNAL,
 	};
 
 	if (argc < 2) {
@@ -297,7 +304,7 @@ int main(const int argc, char *const argv[], char *const *const envp)
 			"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
 			"%s=\"9418\" "
 			"%s=\"80:443\" "
-			"%s=\"a\" "
+			"%s=\"a:s\" "
 			"%s bash -i\n\n",
 			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
 			ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]);
@@ -371,7 +378,8 @@ int main(const int argc, char *const argv[], char *const *const envp)
 		__attribute__((fallthrough));
 	case 5:
 		/* Removes LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */
-		ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
+		ruleset_attr.scoped &= ~(LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET |
+					 LANDLOCK_SCOPED_SIGNAL);
 		fprintf(stderr,
 			"Hint: You should update the running kernel "
 			"to leverage Landlock features "
-- 
2.34.1