From 39705a6c29f8a2b93cf5b99528a55366c50014d1 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 24 Jul 2024 14:49:01 +0200 Subject: [PATCH 1/2] landlock: Don't lose track of restrictions on cred_transfer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When a process' cred struct is replaced, this _almost_ always invokes the cred_prepare LSM hook; but in one special case (when KEYCTL_SESSION_TO_PARENT updates the parent's credentials), the cred_transfer LSM hook is used instead. Landlock only implements the cred_prepare hook, not cred_transfer, so KEYCTL_SESSION_TO_PARENT causes all information on Landlock restrictions to be lost. This basically means that a process with the ability to use the fork() and keyctl() syscalls can get rid of all Landlock restrictions on itself. Fix it by adding a cred_transfer hook that does the same thing as the existing cred_prepare hook. (Implemented by having hook_cred_prepare() call hook_cred_transfer() so that the two functions are less likely to accidentally diverge in the future.) Cc: stable@kernel.org Fixes: 385975dca53e ("landlock: Set up the security framework and manage credentials") Signed-off-by: Jann Horn Link: https://lore.kernel.org/r/20240724-landlock-houdini-fix-v1-1-df89a4560ca3@google.com Signed-off-by: Mickaël Salaün --- security/landlock/cred.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/security/landlock/cred.c b/security/landlock/cred.c index 786af18c4a1c..db9fe7d906ba 100644 --- a/security/landlock/cred.c +++ b/security/landlock/cred.c @@ -14,8 +14,8 @@ #include "ruleset.h" #include "setup.h" -static int hook_cred_prepare(struct cred *const new, - const struct cred *const old, const gfp_t gfp) +static void hook_cred_transfer(struct cred *const new, + const struct cred *const old) { struct landlock_ruleset *const old_dom = landlock_cred(old)->domain; @@ -23,6 +23,12 @@ static int hook_cred_prepare(struct cred *const new, landlock_get_ruleset(old_dom); landlock_cred(new)->domain = old_dom; } +} + +static int hook_cred_prepare(struct cred *const new, + const struct cred *const old, const gfp_t gfp) +{ + hook_cred_transfer(new, old); return 0; } @@ -36,6 +42,7 @@ static void hook_cred_free(struct cred *const cred) static struct security_hook_list landlock_hooks[] __ro_after_init = { LSM_HOOK_INIT(cred_prepare, hook_cred_prepare), + LSM_HOOK_INIT(cred_transfer, hook_cred_transfer), LSM_HOOK_INIT(cred_free, hook_cred_free), }; From cc374782b6ca0fd634482391da977542443d3368 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= Date: Wed, 24 Jul 2024 16:54:26 +0200 Subject: [PATCH 2/2] selftests/landlock: Add cred_transfer test MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Jann Horn Link: https://lore.kernel.org/r/20240724.Ood5aige9she@digikod.net Signed-off-by: Mickaël Salaün --- tools/testing/selftests/landlock/base_test.c | 74 ++++++++++++++++++++ tools/testing/selftests/landlock/config | 1 + 2 files changed, 75 insertions(+) diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c index 3c1e9f35b531..3b26bf3cf5b9 100644 --- a/tools/testing/selftests/landlock/base_test.c +++ b/tools/testing/selftests/landlock/base_test.c @@ -9,6 +9,7 @@ #define _GNU_SOURCE #include #include +#include #include #include #include @@ -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 0086efaa7b68..29af19c4e9f9 100644 --- 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