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, 33 insertions, 0 deletions

diff --git a/fs/lockd/share.h b/fs/lockd/share.h
new file mode 100644
index 000000000..1ec3ccdb2
--- /dev/null
+++ b/fs/lockd/share.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DOS share management for lockd.
+ *
+ * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
+ */
+
+#ifndef _LOCKD_SHARE_H
+#define _LOCKD_SHARE_H
+
+/* Synthetic svid for lockowner lookup during share operations */
+#define LOCKD_SHARE_SVID	(~(u32)0)
+
+/*
+ * DOS share for a specific file
+ */
+struct lockd_share {
+	struct lockd_share *	s_next;		/* linked list */
+	struct nlm_host *	s_host;		/* client host */
+	struct nlm_file *	s_file;		/* shared file */
+	struct xdr_netobj	s_owner;	/* owner handle */
+	u32			s_access;	/* access mode */
+	u32			s_mode;		/* deny mode */
+};
+
+__be32	nlmsvc_share_file(struct nlm_host *host, struct nlm_file *file,
+			  struct xdr_netobj *oh, u32 access, u32 mode);
+__be32	nlmsvc_unshare_file(struct nlm_host *host, struct nlm_file *file,
+			    struct xdr_netobj *oh);
+void	nlmsvc_traverse_shares(struct nlm_host *, struct nlm_file *,
+					       nlm_host_match_fn_t);
+
+#endif /* _LOCKD_SHARE_H */