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, 147 insertions, 0 deletions

diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
new file mode 100644
index 000000000..386fd1c54
--- /dev/null
+++ b/fs/nfsd/debugfs.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/debugfs.h>
+
+#include "nfsd.h"
+
+static struct dentry *nfsd_top_dir __read_mostly;
+
+/*
+ * /sys/kernel/debug/nfsd/disable-splice-read
+ *
+ * Contents:
+ *   %0: NFS READ is allowed to use page splicing
+ *   %1: NFS READ uses only iov iter read
+ *
+ * The default value of this setting is zero (page splicing is
+ * allowed). This setting takes immediate effect for all NFS
+ * versions, all exports, and in all NFSD net namespaces.
+ */
+
+static int nfsd_dsr_get(void *data, u64 *val)
+{
+	*val = nfsd_disable_splice_read ? 1 : 0;
+	return 0;
+}
+
+static int nfsd_dsr_set(void *data, u64 val)
+{
+	nfsd_disable_splice_read = (val > 0);
+	if (!nfsd_disable_splice_read) {
+		/*
+		 * Must use buffered I/O if splice_read is enabled.
+		 */
+		nfsd_io_cache_read = NFSD_IO_BUFFERED;
+	}
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(nfsd_dsr_fops, nfsd_dsr_get, nfsd_dsr_set, "%llu\n");
+
+/*
+ * /sys/kernel/debug/nfsd/io_cache_read
+ *
+ * Contents:
+ *   %0: NFS READ will use buffered IO
+ *   %1: NFS READ will use dontcache (buffered IO w/ dropbehind)
+ *   %2: NFS READ will use direct IO
+ *
+ * This setting takes immediate effect for all NFS versions,
+ * all exports, and in all NFSD net namespaces.
+ */
+
+static int nfsd_io_cache_read_get(void *data, u64 *val)
+{
+	*val = nfsd_io_cache_read;
+	return 0;
+}
+
+static int nfsd_io_cache_read_set(void *data, u64 val)
+{
+	int ret = 0;
+
+	switch (val) {
+	case NFSD_IO_BUFFERED:
+		nfsd_io_cache_read = NFSD_IO_BUFFERED;
+		break;
+	case NFSD_IO_DONTCACHE:
+	case NFSD_IO_DIRECT:
+		/*
+		 * Must disable splice_read when enabling
+		 * NFSD_IO_DONTCACHE.
+		 */
+		nfsd_disable_splice_read = true;
+		nfsd_io_cache_read = val;
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(nfsd_io_cache_read_fops, nfsd_io_cache_read_get,
+			 nfsd_io_cache_read_set, "%llu\n");
+
+/*
+ * /sys/kernel/debug/nfsd/io_cache_write
+ *
+ * Contents:
+ *   %0: NFS WRITE will use buffered IO
+ *   %1: NFS WRITE will use dontcache (buffered IO w/ dropbehind)
+ *
+ * This setting takes immediate effect for all NFS versions,
+ * all exports, and in all NFSD net namespaces.
+ */
+
+static int nfsd_io_cache_write_get(void *data, u64 *val)
+{
+	*val = nfsd_io_cache_write;
+	return 0;
+}
+
+static int nfsd_io_cache_write_set(void *data, u64 val)
+{
+	int ret = 0;
+
+	switch (val) {
+	case NFSD_IO_BUFFERED:
+	case NFSD_IO_DONTCACHE:
+	case NFSD_IO_DIRECT:
+		nfsd_io_cache_write = val;
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(nfsd_io_cache_write_fops, nfsd_io_cache_write_get,
+			 nfsd_io_cache_write_set, "%llu\n");
+
+void nfsd_debugfs_exit(void)
+{
+	debugfs_remove_recursive(nfsd_top_dir);
+	nfsd_top_dir = NULL;
+}
+
+void nfsd_debugfs_init(void)
+{
+	nfsd_top_dir = debugfs_create_dir("nfsd", NULL);
+
+	debugfs_create_file("disable-splice-read", S_IWUSR | S_IRUGO,
+			    nfsd_top_dir, NULL, &nfsd_dsr_fops);
+
+	debugfs_create_file("io_cache_read", 0644, nfsd_top_dir, NULL,
+			    &nfsd_io_cache_read_fops);
+
+	debugfs_create_file("io_cache_write", 0644, nfsd_top_dir, NULL,
+			    &nfsd_io_cache_write_fops);
+#ifdef CONFIG_NFSD_V4
+	debugfs_create_bool("delegated_timestamps", 0644, nfsd_top_dir,
+			    &nfsd_delegts_enabled);
+#endif
+}