openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 249 insertions, 0 deletions

diff --git a/block/ioprio.c b/block/ioprio.c
new file mode 100644
index 000000000..f0ee27985
--- /dev/null
+++ b/block/ioprio.c
@@ -0,0 +1,249 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/ioprio.c
+ *
+ * Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
+ *
+ * Helper functions for setting/querying io priorities of processes. The
+ * system calls closely mimmick getpriority/setpriority, see the man page for
+ * those. The prio argument is a composite of prio class and prio data, where
+ * the data argument has meaning within that class. The standard scheduling
+ * classes have 8 distinct prio levels, with 0 being the highest prio and 7
+ * being the lowest.
+ *
+ * IOW, setting BE scheduling class with prio 2 is done ala:
+ *
+ * unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
+ *
+ * ioprio_set(PRIO_PROCESS, pid, prio);
+ *
+ * See also Documentation/block/ioprio.rst
+ *
+ */
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/ioprio.h>
+#include <linux/cred.h>
+#include <linux/blkdev.h>
+#include <linux/capability.h>
+#include <linux/syscalls.h>
+#include <linux/security.h>
+#include <linux/pid_namespace.h>
+
+int ioprio_check_cap(int ioprio)
+{
+	int class = IOPRIO_PRIO_CLASS(ioprio);
+	int level = IOPRIO_PRIO_LEVEL(ioprio);
+
+	switch (class) {
+		case IOPRIO_CLASS_RT:
+			/*
+			 * Originally this only checked for CAP_SYS_ADMIN,
+			 * which was implicitly allowed for pid 0 by security
+			 * modules such as SELinux. Make sure we check
+			 * CAP_SYS_ADMIN first to avoid a denial/avc for
+			 * possibly missing CAP_SYS_NICE permission.
+			 */
+			if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
+				return -EPERM;
+			break;
+		case IOPRIO_CLASS_BE:
+		case IOPRIO_CLASS_IDLE:
+			break;
+		case IOPRIO_CLASS_NONE:
+			if (level)
+				return -EINVAL;
+			break;
+		case IOPRIO_CLASS_INVALID:
+		default:
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
+{
+	struct task_struct *p, *g;
+	struct user_struct *user;
+	struct pid *pgrp;
+	kuid_t uid;
+	int ret;
+
+	ret = ioprio_check_cap(ioprio);
+	if (ret)
+		return ret;
+
+	ret = -ESRCH;
+	rcu_read_lock();
+	switch (which) {
+		case IOPRIO_WHO_PROCESS:
+			if (!who)
+				p = current;
+			else
+				p = find_task_by_vpid(who);
+			if (p)
+				ret = set_task_ioprio(p, ioprio);
+			break;
+		case IOPRIO_WHO_PGRP:
+			if (!who)
+				pgrp = task_pgrp(current);
+			else
+				pgrp = find_vpid(who);
+
+			read_lock(&tasklist_lock);
+			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
+				ret = set_task_ioprio(p, ioprio);
+				if (ret) {
+					read_unlock(&tasklist_lock);
+					goto out;
+				}
+			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
+			read_unlock(&tasklist_lock);
+
+			break;
+		case IOPRIO_WHO_USER:
+			uid = make_kuid(current_user_ns(), who);
+			if (!uid_valid(uid))
+				break;
+			if (!who)
+				user = current_user();
+			else
+				user = find_user(uid);
+
+			if (!user)
+				break;
+
+			for_each_process_thread(g, p) {
+				if (!uid_eq(task_uid(p), uid) ||
+				    !task_pid_vnr(p))
+					continue;
+				ret = set_task_ioprio(p, ioprio);
+				if (ret)
+					goto free_uid;
+			}
+free_uid:
+			if (who)
+				free_uid(user);
+			break;
+		default:
+			ret = -EINVAL;
+	}
+
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
+static int get_task_ioprio(struct task_struct *p)
+{
+	int ret;
+
+	ret = security_task_getioprio(p);
+	if (ret)
+		goto out;
+	task_lock(p);
+	ret = __get_task_ioprio(p);
+	task_unlock(p);
+out:
+	return ret;
+}
+
+/*
+ * Return raw IO priority value as set by userspace. We use this for
+ * ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
+ * also so that userspace can distinguish unset IO priority (which just gets
+ * overriden based on task's nice value) from IO priority set to some value.
+ */
+static int get_task_raw_ioprio(struct task_struct *p)
+{
+	int ret;
+
+	ret = security_task_getioprio(p);
+	if (ret)
+		goto out;
+	task_lock(p);
+	if (p->io_context)
+		ret = p->io_context->ioprio;
+	else
+		ret = IOPRIO_DEFAULT;
+	task_unlock(p);
+out:
+	return ret;
+}
+
+static int ioprio_best(unsigned short aprio, unsigned short bprio)
+{
+	return min(aprio, bprio);
+}
+
+SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
+{
+	struct task_struct *g, *p;
+	struct user_struct *user;
+	struct pid *pgrp;
+	kuid_t uid;
+	int ret = -ESRCH;
+	int tmpio;
+
+	rcu_read_lock();
+	switch (which) {
+		case IOPRIO_WHO_PROCESS:
+			if (!who)
+				p = current;
+			else
+				p = find_task_by_vpid(who);
+			if (p)
+				ret = get_task_raw_ioprio(p);
+			break;
+		case IOPRIO_WHO_PGRP:
+			if (!who)
+				pgrp = task_pgrp(current);
+			else
+				pgrp = find_vpid(who);
+			read_lock(&tasklist_lock);
+			do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
+				tmpio = get_task_ioprio(p);
+				if (tmpio < 0)
+					continue;
+				if (ret == -ESRCH)
+					ret = tmpio;
+				else
+					ret = ioprio_best(ret, tmpio);
+			} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
+			read_unlock(&tasklist_lock);
+
+			break;
+		case IOPRIO_WHO_USER:
+			uid = make_kuid(current_user_ns(), who);
+			if (!who)
+				user = current_user();
+			else
+				user = find_user(uid);
+
+			if (!user)
+				break;
+
+			for_each_process_thread(g, p) {
+				if (!uid_eq(task_uid(p), user->uid) ||
+				    !task_pid_vnr(p))
+					continue;
+				tmpio = get_task_ioprio(p);
+				if (tmpio < 0)
+					continue;
+				if (ret == -ESRCH)
+					ret = tmpio;
+				else
+					ret = ioprio_best(ret, tmpio);
+			}
+
+			if (who)
+				free_uid(user);
+			break;
+		default:
+			ret = -EINVAL;
+	}
+
+	rcu_read_unlock();
+	return ret;
+}