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, 141 insertions, 0 deletions

diff --git a/io_uring/notif.c b/io_uring/notif.c
new file mode 100644
index 000000000..efce8ae12
--- /dev/null
+++ b/io_uring/notif.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+#include <linux/net.h>
+#include <linux/io_uring.h>
+
+#include "io_uring.h"
+#include "notif.h"
+#include "rsrc.h"
+
+static const struct ubuf_info_ops io_ubuf_ops;
+
+static void io_notif_tw_complete(struct io_tw_req tw_req, io_tw_token_t tw)
+{
+	struct io_kiocb *notif = tw_req.req;
+	struct io_notif_data *nd = io_notif_to_data(notif);
+	struct io_ring_ctx *ctx = notif->ctx;
+
+	lockdep_assert_held(&ctx->uring_lock);
+
+	do {
+		notif = cmd_to_io_kiocb(nd);
+
+		if (WARN_ON_ONCE(ctx != notif->ctx))
+			return;
+		lockdep_assert(refcount_read(&nd->uarg.refcnt) == 0);
+
+		if (unlikely(nd->zc_report) && (nd->zc_copied || !nd->zc_used))
+			notif->cqe.res |= IORING_NOTIF_USAGE_ZC_COPIED;
+
+		if (nd->account_pages && notif->ctx->user) {
+			__io_unaccount_mem(notif->ctx->user, nd->account_pages);
+			nd->account_pages = 0;
+		}
+
+		nd = nd->next;
+		io_req_task_complete((struct io_tw_req){notif}, tw);
+	} while (nd);
+}
+
+void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg,
+			 bool success)
+{
+	struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
+	struct io_kiocb *notif = cmd_to_io_kiocb(nd);
+	unsigned tw_flags;
+
+	if (nd->zc_report) {
+		if (success && !nd->zc_used && skb)
+			WRITE_ONCE(nd->zc_used, true);
+		else if (!success && !nd->zc_copied)
+			WRITE_ONCE(nd->zc_copied, true);
+	}
+
+	if (!refcount_dec_and_test(&uarg->refcnt))
+		return;
+
+	if (nd->head != nd) {
+		io_tx_ubuf_complete(skb, &nd->head->uarg, success);
+		return;
+	}
+
+	tw_flags = nd->next ? 0 : IOU_F_TWQ_LAZY_WAKE;
+	notif->io_task_work.func = io_notif_tw_complete;
+	__io_req_task_work_add(notif, tw_flags);
+}
+
+static int io_link_skb(struct sk_buff *skb, struct ubuf_info *uarg)
+{
+	struct io_notif_data *nd, *prev_nd;
+	struct io_kiocb *prev_notif, *notif;
+	struct ubuf_info *prev_uarg = skb_zcopy(skb);
+
+	nd = container_of(uarg, struct io_notif_data, uarg);
+	notif = cmd_to_io_kiocb(nd);
+
+	if (!prev_uarg) {
+		net_zcopy_get(&nd->uarg);
+		skb_zcopy_init(skb, &nd->uarg);
+		return 0;
+	}
+	/* handle it separately as we can't link a notif to itself */
+	if (unlikely(prev_uarg == &nd->uarg))
+		return 0;
+	/* we can't join two links together, just request a fresh skb */
+	if (unlikely(nd->head != nd || nd->next))
+		return -EEXIST;
+	/* don't mix zc providers */
+	if (unlikely(prev_uarg->ops != &io_ubuf_ops))
+		return -EEXIST;
+
+	prev_nd = container_of(prev_uarg, struct io_notif_data, uarg);
+	prev_notif = cmd_to_io_kiocb(prev_nd);
+
+	/* make sure all notifications can be finished in the same task_work */
+	if (unlikely(notif->ctx != prev_notif->ctx ||
+		     notif->tctx != prev_notif->tctx))
+		return -EEXIST;
+
+	nd->head = prev_nd->head;
+	nd->next = prev_nd->next;
+	prev_nd->next = nd;
+	net_zcopy_get(&nd->head->uarg);
+	return 0;
+}
+
+static const struct ubuf_info_ops io_ubuf_ops = {
+	.complete = io_tx_ubuf_complete,
+	.link_skb = io_link_skb,
+};
+
+struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
+	__must_hold(&ctx->uring_lock)
+{
+	struct io_kiocb *notif;
+	struct io_notif_data *nd;
+
+	if (unlikely(!io_alloc_req(ctx, &notif)))
+		return NULL;
+	notif->ctx = ctx;
+	notif->opcode = IORING_OP_NOP;
+	notif->flags = 0;
+	notif->file = NULL;
+	notif->tctx = current->io_uring;
+	io_get_task_refs(1);
+	notif->file_node = NULL;
+	notif->buf_node = NULL;
+
+	nd = io_notif_to_data(notif);
+	nd->zc_report = false;
+	nd->account_pages = 0;
+	nd->next = NULL;
+	nd->head = nd;
+
+	nd->uarg.flags = IO_NOTIF_UBUF_FLAGS;
+	nd->uarg.ops = &io_ubuf_ops;
+	refcount_set(&nd->uarg.refcnt, 1);
+	return notif;
+}