diff --git a/fs/exec.c b/fs/exec.c
index db17be51b112..0e46ec57fe0a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1010,16 +1010,26 @@ ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len)
}
EXPORT_SYMBOL(read_code);
+/*
+ * Maps the mm_struct mm into the current task struct.
+ * On success, this function returns with the mutex
+ * exec_update_mutex locked.
+ */
static int exec_mmap(struct mm_struct *mm)
{
struct task_struct *tsk;
struct mm_struct *old_mm, *active_mm;
+ int ret;
/* Notify parent that we're no longer interested in the old VM */
tsk = current;
old_mm = current->mm;
exec_mm_release(tsk, old_mm);
+ ret = mutex_lock_killable(&tsk->signal->exec_update_mutex);
+ if (ret)
+ return ret;
+
if (old_mm) {
sync_mm_rss(old_mm);
/*
@@ -1031,9 +1041,11 @@ static int exec_mmap(struct mm_struct *mm)
down_read(&old_mm->mmap_sem);
if (unlikely(old_mm->core_state)) {
up_read(&old_mm->mmap_sem);
+ mutex_unlock(&tsk->signal->exec_update_mutex);
return -EINTR;
}
}
+
task_lock(tsk);
active_mm = tsk->active_mm;
membarrier_exec_mmap(mm);
@@ -1189,10 +1201,22 @@ no_thread_group:
/* we have changed execution domain */
tsk->exit_signal = SIGCHLD;
-#ifdef CONFIG_POSIX_TIMERS
- exit_itimers(sig);
- flush_itimer_signals();
-#endif
+ BUG_ON(!thread_group_leader(tsk));
+ return 0;
+
+killed:
+ /* protects against exit_notify() and __exit_signal() */
+ read_lock(&tasklist_lock);
+ sig->group_exit_task = NULL;
+ sig->notify_count = 0;
+ read_unlock(&tasklist_lock);
+ return -EAGAIN;
+}
+
+
+static int unshare_sighand(struct task_struct *me)
+{
+ struct sighand_struct *oldsighand = me->sighand;
if (refcount_read(&oldsighand->count) != 1) {
struct sighand_struct *newsighand;
@@ -1210,23 +1234,13 @@ no_thread_group:
write_lock_irq(&tasklist_lock);
spin_lock(&oldsighand->siglock);
- rcu_assign_pointer(tsk->sighand, newsighand);
+ rcu_assign_pointer(me->sighand, newsighand);
spin_unlock(&oldsighand->siglock);
write_unlock_irq(&tasklist_lock);
__cleanup_sighand(oldsighand);
}
-
- BUG_ON(!thread_group_leader(tsk));
return 0;
-
-killed:
- /* protects against exit_notify() and __exit_signal() */
- read_lock(&tasklist_lock);
- sig->group_exit_task = NULL;
- sig->notify_count = 0;
- read_unlock(&tasklist_lock);
- return -EAGAIN;
}
char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk)
@@ -1260,13 +1274,13 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
*/
int flush_old_exec(struct linux_binprm * bprm)
{
+ struct task_struct *me = current;
int retval;
/*
- * Make sure we have a private signal table and that
- * we are unassociated from the previous thread group.
+ * Make this the only thread in the thread group.
*/
- retval = de_thread(current);
+ retval = de_thread(me);
if (retval)
goto out;
@@ -1286,18 +1300,31 @@ int flush_old_exec(struct linux_binprm * bprm)
goto out;
/*
- * After clearing bprm->mm (to mark that current is using the
- * prepared mm now), we have nothing left of the original
+ * After setting bprm->called_exec_mmap (to mark that current is
+ * using the prepared mm now), we have nothing left of the original
* process. If anything from here on returns an error, the check
* in search_binary_handler() will SEGV current.
*/
+ bprm->called_exec_mmap = 1;
bprm->mm = NULL;
+#ifdef CONFIG_POSIX_TIMERS
+ exit_itimers(me->signal);
+ flush_itimer_signals();
+#endif
+
+ /*
+ * Make the signal table private.
+ */
+ retval = unshare_sighand(me);
+ if (retval)
+ goto out;
+
set_fs(USER_DS);
- current->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
+ me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
PF_NOFREEZE | PF_NO_SETAFFINITY);
flush_thread();
- current->personality &= ~bprm->per_clear;
+ me->personality &= ~bprm->per_clear;
/*
* We have to apply CLOEXEC before we change whether the process is
@@ -1305,7 +1332,7 @@ int flush_old_exec(struct linux_binprm * bprm)
* trying to access the should-be-closed file descriptors of a process
* undergoing exec(2).
*/
- do_close_on_exec(current->files);
+ do_close_on_exec(me->files);
return 0;
out:
@@ -1424,6 +1451,8 @@ static void free_bprm(struct linux_binprm *bprm)
{
free_arg_pages(bprm);
if (bprm->cred) {
+ if (bprm->called_exec_mmap)
+ mutex_unlock(¤t->signal->exec_update_mutex);
mutex_unlock(¤t->signal->cred_guard_mutex);
abort_creds(bprm->cred);
}
@@ -1473,6 +1502,7 @@ void install_exec_creds(struct linux_binprm *bprm)
* credentials; any time after this it may be unlocked.
*/
security_bprm_committed_creds(bprm);
+ mutex_unlock(¤t->signal->exec_update_mutex);
mutex_unlock(¤t->signal->cred_guard_mutex);
}
EXPORT_SYMBOL(install_exec_creds);
@@ -1664,7 +1694,7 @@ int search_binary_handler(struct linux_binprm *bprm)
read_lock(&binfmt_lock);
put_binfmt(fmt);
- if (retval < 0 && !bprm->mm) {
+ if (retval < 0 && bprm->called_exec_mmap) {
/* we got to flush_old_exec() and failed after it */
read_unlock(&binfmt_lock);
force_sigsegv(SIGSEGV);
diff --git a/fs/proc/base.c b/fs/proc/base.c
index e7efe9d6f3d6..74f948a6b621 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -405,11 +405,11 @@ print0:
static int lock_trace(struct task_struct *task)
{
- int err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ int err = mutex_lock_killable(&task->signal->exec_update_mutex);
if (err)
return err;
if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) {
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
return -EPERM;
}
return 0;
@@ -417,7 +417,7 @@ static int lock_trace(struct task_struct *task)
static void unlock_trace(struct task_struct *task)
{
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
}
#ifdef CONFIG_STACKTRACE
@@ -2883,7 +2883,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
unsigned long flags;
int result;
- result = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ result = mutex_lock_killable(&task->signal->exec_update_mutex);
if (result)
return result;
@@ -2919,7 +2919,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
result = 0;
out_unlock:
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
return result;
}
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index b40fc633f3be..a345d9fed3d8 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -44,7 +44,13 @@ struct linux_binprm {
* exec has happened. Used to sanitize execution environment
* and to set AT_SECURE auxv for glibc.
*/
- secureexec:1;
+ secureexec:1,
+ /*
+ * Set by flush_old_exec, when exec_mmap has been called.
+ * This is past the point of no return, when the
+ * exec_update_mutex has been taken.
+ */
+ called_exec_mmap:1;
#ifdef __alpha__
unsigned int taso:1;
#endif
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 88050259c466..a29df79540ce 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -224,7 +224,14 @@ struct signal_struct {
struct mutex cred_guard_mutex; /* guard against foreign influences on
* credential calculations
- * (notably. ptrace) */
+ * (notably. ptrace)
+ * Deprecated do not use in new code.
+ * Use exec_update_mutex instead.
+ */
+ struct mutex exec_update_mutex; /* Held while task_struct is being
+ * updated during exec, and may have
+ * inconsistent permissions.
+ */
} __randomize_layout;
/*
diff --git a/init/init_task.c b/init/init_task.c
index 9e5cbe5eab7b..bd403ed3e418 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -26,6 +26,7 @@ static struct signal_struct init_signals = {
.multiprocess = HLIST_HEAD_INIT,
.rlim = INIT_RLIMITS,
.cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex),
+ .exec_update_mutex = __MUTEX_INITIALIZER(init_signals.exec_update_mutex),
#ifdef CONFIG_POSIX_TIMERS
.posix_timers = LIST_HEAD_INIT(init_signals.posix_timers),
.cputimer = {
diff --git a/kernel/cred.c b/kernel/cred.c
index 809a985b1793..71a792616917 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -675,8 +675,6 @@ void __init cred_init(void)
* The caller may change these controls afterwards if desired.
*
* Returns the new credentials or NULL if out of memory.
- *
- * Does not take, and does not return holding current->cred_replace_mutex.
*/
struct cred *prepare_kernel_cred(struct task_struct *daemon)
{
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e453589da97c..71cba8cfccbc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1249,7 +1249,7 @@ static void put_ctx(struct perf_event_context *ctx)
* function.
*
* Lock order:
- * cred_guard_mutex
+ * exec_update_mutex
* task_struct::perf_event_mutex
* perf_event_context::mutex
* perf_event::child_mutex;
@@ -11263,14 +11263,14 @@ SYSCALL_DEFINE5(perf_event_open,
}
if (task) {
- err = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
+ err = mutex_lock_interruptible(&task->signal->exec_update_mutex);
if (err)
goto err_task;
/*
* Reuse ptrace permission checks for now.
*
- * We must hold cred_guard_mutex across this and any potential
+ * We must hold exec_update_mutex across this and any potential
* perf_install_in_context() call for this new event to
* serialize against exec() altering our credentials (and the
* perf_event_exit_task() that could imply).
@@ -11559,7 +11559,7 @@ SYSCALL_DEFINE5(perf_event_open,
mutex_unlock(&ctx->mutex);
if (task) {
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
put_task_struct(task);
}
@@ -11595,7 +11595,7 @@ err_alloc:
free_event(event);
err_cred:
if (task)
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
err_task:
if (task)
put_task_struct(task);
@@ -11900,7 +11900,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
/*
* When a child task exits, feed back event values to parent events.
*
- * Can be called with cred_guard_mutex held when called from
+ * Can be called with exec_update_mutex held when called from
* install_exec_creds().
*/
void perf_event_exit_task(struct task_struct *child)
diff --git a/kernel/fork.c b/kernel/fork.c
index 60a1295f4384..e0668a79bca1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1224,7 +1224,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
struct mm_struct *mm;
int err;
- err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ err = mutex_lock_killable(&task->signal->exec_update_mutex);
if (err)
return ERR_PTR(err);
@@ -1234,7 +1234,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
mmput(mm);
mm = ERR_PTR(-EACCES);
}
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
return mm;
}
@@ -1594,6 +1594,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
sig->oom_score_adj_min = current->signal->oom_score_adj_min;
mutex_init(&sig->cred_guard_mutex);
+ mutex_init(&sig->exec_update_mutex);
return 0;
}
diff --git a/kernel/kcmp.c b/kernel/kcmp.c
index a0e3d7a0e8b8..b3ff9288c6cc 100644
--- a/kernel/kcmp.c
+++ b/kernel/kcmp.c
@@ -173,8 +173,8 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
/*
* One should have enough rights to inspect task details.
*/
- ret = kcmp_lock(&task1->signal->cred_guard_mutex,
- &task2->signal->cred_guard_mutex);
+ ret = kcmp_lock(&task1->signal->exec_update_mutex,
+ &task2->signal->exec_update_mutex);
if (ret)
goto err;
if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
@@ -229,8 +229,8 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
}
err_unlock:
- kcmp_unlock(&task1->signal->cred_guard_mutex,
- &task2->signal->cred_guard_mutex);
+ kcmp_unlock(&task1->signal->exec_update_mutex,
+ &task2->signal->exec_update_mutex);
err:
put_task_struct(task1);
put_task_struct(task2);
diff --git a/kernel/pid.c b/kernel/pid.c
index 60820e72634c..efd34874b3d1 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -577,7 +577,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
struct file *file;
int ret;
- ret = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ ret = mutex_lock_killable(&task->signal->exec_update_mutex);
if (ret)
return ERR_PTR(ret);
@@ -586,7 +586,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
else
file = ERR_PTR(-EPERM);
- mutex_unlock(&task->signal->cred_guard_mutex);
+ mutex_unlock(&task->signal->exec_update_mutex);
return file ?: ERR_PTR(-EBADF);
}
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index de41e830cdac..74e957e302fe 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -206,7 +206,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
if (!mm || IS_ERR(mm)) {
rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
/*
- * Explicitly map EACCES to EPERM as EPERM is a more a
+ * Explicitly map EACCES to EPERM as EPERM is a more
* appropriate error code for process_vw_readv/writev
*/
if (rc == -EACCES)
diff --git a/tools/testing/selftests/ptrace/Makefile b/tools/testing/selftests/ptrace/Makefile
index c0b7f89f0930..2f1f532c39db 100644
--- a/tools/testing/selftests/ptrace/Makefile
+++ b/tools/testing/selftests/ptrace/Makefile
@@ -1,6 +1,6 @@
# SPDX-License-Identifier: GPL-2.0-only
-CFLAGS += -iquote../../../../include/uapi -Wall
+CFLAGS += -std=c99 -pthread -iquote../../../../include/uapi -Wall
-TEST_GEN_PROGS := get_syscall_info peeksiginfo
+TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess
include ../lib.mk
diff --git a/tools/testing/selftests/ptrace/vmaccess.c b/tools/testing/selftests/ptrace/vmaccess.c
new file mode 100644
index 000000000000..4db327b44586
--- /dev/null
+++ b/tools/testing/selftests/ptrace/vmaccess.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2020 Bernd Edlinger <bernd.edlinger@hotmail.de>
+ * All rights reserved.
+ *
+ * Check whether /proc/$pid/mem can be accessed without causing deadlocks
+ * when de_thread is blocked with ->cred_guard_mutex held.
+ */
+
+#include "../kselftest_harness.h"
+#include <stdio.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/ptrace.h>
+
+static void *thread(void *arg)
+{
+ ptrace(PTRACE_TRACEME, 0, 0L, 0L);
+ return NULL;
+}
+
+TEST(vmaccess)
+{
+ int f, pid = fork();
+ char mm[64];
+
+ if (!pid) {
+ pthread_t pt;
+
+ pthread_create(&pt, NULL, thread, NULL);
+ pthread_join(pt, NULL);
+ execlp("true", "true", NULL);
+ }
+
+ sleep(1);
+ sprintf(mm, "/proc/%d/mem", pid);
+ f = open(mm, O_RDONLY);
+ ASSERT_GE(f, 0);
+ close(f);
+ f = kill(pid, SIGCONT);
+ ASSERT_EQ(f, 0);
+}
+
+TEST(attach)
+{
+ int s, k, pid = fork();
+
+ if (!pid) {
+ pthread_t pt;
+
+ pthread_create(&pt, NULL, thread, NULL);
+ pthread_join(pt, NULL);
+ execlp("sleep", "sleep", "2", NULL);
+ }
+
+ sleep(1);
+ k = ptrace(PTRACE_ATTACH, pid, 0L, 0L);
+ ASSERT_EQ(errno, EAGAIN);
+ ASSERT_EQ(k, -1);
+ k = waitpid(-1, &s, WNOHANG);
+ ASSERT_NE(k, -1);
+ ASSERT_NE(k, 0);
+ ASSERT_NE(k, pid);
+ ASSERT_EQ(WIFEXITED(s), 1);
+ ASSERT_EQ(WEXITSTATUS(s), 0);
+ sleep(1);
+ k = ptrace(PTRACE_ATTACH, pid, 0L, 0L);
+ ASSERT_EQ(k, 0);
+ k = waitpid(-1, &s, 0);
+ ASSERT_EQ(k, pid);
+ ASSERT_EQ(WIFSTOPPED(s), 1);
+ ASSERT_EQ(WSTOPSIG(s), SIGSTOP);
+ k = ptrace(PTRACE_DETACH, pid, 0L, 0L);
+ ASSERT_EQ(k, 0);
+ k = waitpid(-1, &s, 0);
+ ASSERT_EQ(k, pid);
+ ASSERT_EQ(WIFEXITED(s), 1);
+ ASSERT_EQ(WEXITSTATUS(s), 0);
+ k = waitpid(-1, NULL, 0);
+ ASSERT_EQ(k, -1);
+ ASSERT_EQ(errno, ECHILD);
+}
+
+TEST_HARNESS_MAIN