selftests/landlock: Add cred_transfer test

Check that keyctl(KEYCTL_SESSION_TO_PARENT) preserves the parent's
restrictions.

Fixes: e1199815b47b ("selftests/landlock: Add user space tests")
Co-developed-by: Jann Horn <jannh@google.com>
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20240724.Ood5aige9she@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index 3c1e9f35b53123038082818840176a99632905b3..3b26bf3cf5b9a489e037f5b11b2a635ccb55b83a 100644 (file)
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -9,6 +9,7 @@
 #define _GNU_SOURCE
 #include <errno.h>
 #include <fcntl.h>
+#include <linux/keyctl.h>
 #include <linux/landlock.h>
 #include <string.h>
 #include <sys/prctl.h>
@@ -326,4 +327,77 @@ TEST(ruleset_fd_transfer)
        ASSERT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
 }
 
+TEST(cred_transfer)
+{
+       struct landlock_ruleset_attr ruleset_attr = {
+               .handled_access_fs = LANDLOCK_ACCESS_FS_READ_DIR,
+       };
+       int ruleset_fd, dir_fd;
+       pid_t child;
+       int status;
+
+       drop_caps(_metadata);
+
+       dir_fd = open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
+       EXPECT_LE(0, dir_fd);
+       EXPECT_EQ(0, close(dir_fd));
+
+       /* Denies opening directories. */
+       ruleset_fd =
+               landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+       ASSERT_LE(0, ruleset_fd);
+       EXPECT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+       ASSERT_EQ(0, landlock_restrict_self(ruleset_fd, 0));
+       EXPECT_EQ(0, close(ruleset_fd));
+
+       /* Checks ruleset enforcement. */
+       EXPECT_EQ(-1, open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+       EXPECT_EQ(EACCES, errno);
+
+       /* Needed for KEYCTL_SESSION_TO_PARENT permission checks */
+       EXPECT_NE(-1, syscall(__NR_keyctl, KEYCTL_JOIN_SESSION_KEYRING, NULL, 0,
+                             0, 0))
+       {
+               TH_LOG("Failed to join session keyring: %s", strerror(errno));
+       }
+
+       child = fork();
+       ASSERT_LE(0, child);
+       if (child == 0) {
+               /* Checks ruleset enforcement. */
+               EXPECT_EQ(-1, open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+               EXPECT_EQ(EACCES, errno);
+
+               /*
+                * KEYCTL_SESSION_TO_PARENT is a no-op unless we have a
+                * different session keyring in the child, so make that happen.
+                */
+               EXPECT_NE(-1, syscall(__NR_keyctl, KEYCTL_JOIN_SESSION_KEYRING,
+                                     NULL, 0, 0, 0));
+
+               /*
+                * KEYCTL_SESSION_TO_PARENT installs credentials on the parent
+                * that never go through the cred_prepare hook, this path uses
+                * cred_transfer instead.
+                */
+               EXPECT_EQ(0, syscall(__NR_keyctl, KEYCTL_SESSION_TO_PARENT, 0,
+                                    0, 0, 0));
+
+               /* Re-checks ruleset enforcement. */
+               EXPECT_EQ(-1, open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+               EXPECT_EQ(EACCES, errno);
+
+               _exit(_metadata->exit_code);
+               return;
+       }
+
+       EXPECT_EQ(child, waitpid(child, &status, 0));
+       EXPECT_EQ(1, WIFEXITED(status));
+       EXPECT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
+
+       /* Re-checks ruleset enforcement. */
+       EXPECT_EQ(-1, open("/", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
+       EXPECT_EQ(EACCES, errno);
+}
+
 TEST_HARNESS_MAIN

diff --git a/tools/testing/selftests/landlock/config b/tools/testing/selftests/landlock/config
index 0086efaa7b681c7be4866b4e4b5d9cb924fe150d..29af19c4e9f981923e231112efb5b4cf08dce3b4 100644 (file)
--- a/tools/testing/selftests/landlock/config
+++ b/tools/testing/selftests/landlock/config
@@ -2,6 +2,7 @@ CONFIG_CGROUPS=y
 CONFIG_CGROUP_SCHED=y
 CONFIG_INET=y
 CONFIG_IPV6=y
+CONFIG_KEYS=y
 CONFIG_NET=y
 CONFIG_NET_NS=y
 CONFIG_OVERLAY_FS=y