diff options
| -rw-r--r-- | security/landlock/errata/abi-6.h | 19 | ||||
| -rw-r--r-- | security/landlock/fs.c | 39 | ||||
| -rw-r--r-- | security/landlock/task.c | 12 | ||||
| -rw-r--r-- | tools/testing/selftests/landlock/scoped_signal_test.c | 2 |
4 files changed, 65 insertions, 7 deletions
diff --git a/security/landlock/errata/abi-6.h b/security/landlock/errata/abi-6.h new file mode 100644 index 000000000000..df7bc0e1fdf4 --- /dev/null +++ b/security/landlock/errata/abi-6.h @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +/** + * DOC: erratum_2 + * + * Erratum 2: Scoped signal handling + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * This fix addresses an issue where signal scoping was overly restrictive, + * preventing sandboxed threads from signaling other threads within the same + * process if they belonged to different domains. Because threads are not + * security boundaries, user space might assume that any thread within the same + * process can send signals between themselves (see :manpage:`nptl(7)` and + * :manpage:`libpsx(3)`). Consistent with :manpage:`ptrace(2)` behavior, direct + * interaction between threads of the same process should always be allowed. + * This change ensures that any thread is allowed to send signals to any other + * thread within the same process, regardless of their domain. + */ +LANDLOCK_ERRATUM(2) diff --git a/security/landlock/fs.c b/security/landlock/fs.c index 71b9dc331aae..c19aab87c4d2 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -27,7 +27,9 @@ #include <linux/mount.h> #include <linux/namei.h> #include <linux/path.h> +#include <linux/pid.h> #include <linux/rcupdate.h> +#include <linux/sched/signal.h> #include <linux/spinlock.h> #include <linux/stat.h> #include <linux/types.h> @@ -1628,21 +1630,46 @@ static int hook_file_ioctl_compat(struct file *file, unsigned int cmd, return -EACCES; } -static void hook_file_set_fowner(struct file *file) +/* + * Always allow sending signals between threads of the same process. This + * ensures consistency with hook_task_kill(). + */ +static bool control_current_fowner(struct fown_struct *const fown) { - struct landlock_ruleset *new_dom, *prev_dom; + struct task_struct *p; /* * Lock already held by __f_setown(), see commit 26f204380a3c ("fs: Fix * file_set_fowner LSM hook inconsistencies"). */ - lockdep_assert_held(&file_f_owner(file)->lock); - new_dom = landlock_get_current_domain(); - landlock_get_ruleset(new_dom); + lockdep_assert_held(&fown->lock); + + /* + * Some callers (e.g. fcntl_dirnotify) may not be in an RCU read-side + * critical section. + */ + guard(rcu)(); + p = pid_task(fown->pid, fown->pid_type); + if (!p) + return true; + + return !same_thread_group(p, current); +} + +static void hook_file_set_fowner(struct file *file) +{ + struct landlock_ruleset *prev_dom; + struct landlock_ruleset *new_dom = NULL; + + if (control_current_fowner(file_f_owner(file))) { + new_dom = landlock_get_current_domain(); + landlock_get_ruleset(new_dom); + } + prev_dom = landlock_file(file)->fown_domain; landlock_file(file)->fown_domain = new_dom; - /* Called in an RCU read-side critical section. */ + /* May be called in an RCU read-side critical section. */ landlock_put_ruleset_deferred(prev_dom); } diff --git a/security/landlock/task.c b/security/landlock/task.c index dc7dab78392e..4578ce6e319d 100644 --- a/security/landlock/task.c +++ b/security/landlock/task.c @@ -13,6 +13,7 @@ #include <linux/lsm_hooks.h> #include <linux/rcupdate.h> #include <linux/sched.h> +#include <linux/sched/signal.h> #include <net/af_unix.h> #include <net/sock.h> @@ -264,6 +265,17 @@ static int hook_task_kill(struct task_struct *const p, /* Dealing with USB IO. */ dom = landlock_cred(cred)->domain; } else { + /* + * Always allow sending signals between threads of the same process. + * This is required for process credential changes by the Native POSIX + * Threads Library and implemented by the set*id(2) wrappers and + * libcap(3) with tgkill(2). See nptl(7) and libpsx(3). + * + * This exception is similar to the __ptrace_may_access() one. + */ + if (same_thread_group(p, current)) + return 0; + dom = landlock_get_current_domain(); } dom = landlock_get_applicable_domain(dom, signal_scope); diff --git a/tools/testing/selftests/landlock/scoped_signal_test.c b/tools/testing/selftests/landlock/scoped_signal_test.c index 475ee62a832d..767f117703b7 100644 --- a/tools/testing/selftests/landlock/scoped_signal_test.c +++ b/tools/testing/selftests/landlock/scoped_signal_test.c @@ -281,7 +281,7 @@ TEST(signal_scoping_threads) /* Restricts the domain after creating the first thread. */ create_scoped_domain(_metadata, LANDLOCK_SCOPE_SIGNAL); - ASSERT_EQ(EPERM, pthread_kill(no_sandbox_thread, 0)); + ASSERT_EQ(0, pthread_kill(no_sandbox_thread, 0)); ASSERT_EQ(1, write(thread_pipe[1], ".", 1)); ASSERT_EQ(0, pthread_create(&scoped_thread, NULL, thread_func, NULL)); |