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, 119 insertions, 0 deletions

diff --git a/include/net/scm.h b/include/net/scm.h
new file mode 100644
index 000000000..c52519669
--- /dev/null
+++ b/include/net/scm.h
@@ -0,0 +1,119 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_NET_SCM_H
+#define __LINUX_NET_SCM_H
+
+#include <linux/limits.h>
+#include <linux/net.h>
+#include <linux/cred.h>
+#include <linux/file.h>
+#include <linux/security.h>
+#include <linux/pid.h>
+#include <linux/nsproxy.h>
+#include <linux/sched/signal.h>
+#include <net/compat.h>
+
+/* Well, we should have at least one descriptor open
+ * to accept passed FDs 8)
+ */
+#define SCM_MAX_FD	253
+
+struct scm_creds {
+	u32	pid;
+	kuid_t	uid;
+	kgid_t	gid;
+};
+
+#ifdef CONFIG_UNIX
+struct unix_edge;
+#endif
+
+struct scm_fp_list {
+	short			count;
+	short			count_unix;
+	short			max;
+#ifdef CONFIG_UNIX
+	bool			inflight;
+	bool			dead;
+	struct list_head	vertices;
+	struct unix_edge	*edges;
+#endif
+	struct user_struct	*user;
+	struct file		*fp[SCM_MAX_FD];
+};
+
+struct scm_cookie {
+	struct pid		*pid;		/* Skb credentials */
+	struct scm_fp_list	*fp;		/* Passed files		*/
+	struct scm_creds	creds;		/* Skb credentials	*/
+#ifdef CONFIG_SECURITY_NETWORK
+	u32			secid;		/* Passed security ID 	*/
+#endif
+};
+
+void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm);
+void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm);
+int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm);
+void __scm_destroy(struct scm_cookie *scm);
+struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl);
+
+#ifdef CONFIG_SECURITY_NETWORK
+static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
+{
+	security_socket_getpeersec_dgram(sock, NULL, &scm->secid);
+}
+#else
+static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
+{ }
+#endif /* CONFIG_SECURITY_NETWORK */
+
+static __inline__ void scm_set_cred(struct scm_cookie *scm,
+				    struct pid *pid, kuid_t uid, kgid_t gid)
+{
+	scm->pid = get_pid(pid);
+	scm->creds.pid = pid_vnr(pid);
+	scm->creds.uid = uid;
+	scm->creds.gid = gid;
+}
+
+static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
+{
+	put_pid(scm->pid);
+	scm->pid = NULL;
+}
+
+static __inline__ void scm_destroy(struct scm_cookie *scm)
+{
+	scm_destroy_cred(scm);
+	if (scm->fp)
+		__scm_destroy(scm);
+}
+
+static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
+			       struct scm_cookie *scm, bool forcecreds)
+{
+	memset(scm, 0, sizeof(*scm));
+	scm->creds.uid = INVALID_UID;
+	scm->creds.gid = INVALID_GID;
+	if (forcecreds)
+		scm_set_cred(scm, task_tgid(current), current_uid(), current_gid());
+	unix_get_peersec_dgram(sock, scm);
+	if (msg->msg_controllen <= 0)
+		return 0;
+	return __scm_send(sock, msg, scm);
+}
+
+void scm_recv(struct socket *sock, struct msghdr *msg,
+	      struct scm_cookie *scm, int flags);
+void scm_recv_unix(struct socket *sock, struct msghdr *msg,
+		   struct scm_cookie *scm, int flags);
+
+static inline int scm_recv_one_fd(struct file *f, int __user *ufd,
+				  unsigned int flags)
+{
+	if (!ufd)
+		return -EFAULT;
+	return receive_fd(f, ufd, flags);
+}
+
+#endif /* __LINUX_NET_SCM_H */
+