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, 99 insertions, 0 deletions

diff --git a/fs/fuse/req.c b/fs/fuse/req.c
new file mode 100644
index 000000000..a01ee743d
--- /dev/null
+++ b/fs/fuse/req.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "dev.h"
+#include "fuse_i.h"
+
+static int fuse_fill_creds(struct fuse_mount *fm, struct fuse_args *args, struct mnt_idmap *idmap)
+{
+	struct fuse_conn *fc = fm->fc;
+	bool no_idmap = !fm->sb || (fm->sb->s_iflags & SB_I_NOIDMAP);
+	kuid_t fsuid = mapped_fsuid(idmap, fc->user_ns);
+	kgid_t fsgid = mapped_fsgid(idmap, fc->user_ns);
+
+	args->pid = pid_nr_ns(task_pid(current), fc->pid_ns);
+
+	if (args->force) {
+		if (args->nocreds)
+			return 0;
+
+		if (no_idmap) {
+			args->uid = from_kuid_munged(fc->user_ns, current_fsuid());
+			args->gid = from_kgid_munged(fc->user_ns, current_fsgid());
+		} else {
+			args->uid = FUSE_INVALID_UIDGID;
+			args->gid = FUSE_INVALID_UIDGID;
+		}
+		return 0;
+	}
+
+	WARN_ON(args->nocreds);
+	/*
+	 * Keep the old behavior when idmappings support was not
+	 * declared by a FUSE server.
+	 *
+	 * For those FUSE servers who support idmapped mounts, we send UID/GID
+	 * only along with "inode creation" fuse requests, otherwise idmap ==
+	 * &invalid_mnt_idmap and req->in.h.{u,g}id will be equal to
+	 * FUSE_INVALID_UIDGID.
+	 */
+	if (no_idmap) {
+		fsuid = current_fsuid();
+		fsgid = current_fsgid();
+	}
+	args->uid = from_kuid(fc->user_ns, fsuid);
+	args->gid = from_kgid(fc->user_ns, fsgid);
+
+	if (no_idmap && unlikely(args->uid == ((uid_t)-1) || args->gid == ((gid_t)-1)))
+		return -EOVERFLOW;
+
+	return 0;
+}
+
+static int fuse_req_prep(struct fuse_mount *fm, struct fuse_args *args, struct mnt_idmap *idmap)
+{
+	if (!args->force && fm->fc->conn_error)
+		return -ECONNREFUSED;
+
+	return fuse_fill_creds(fm, args, idmap);
+}
+
+ssize_t __fuse_simple_request(struct mnt_idmap *idmap, struct fuse_mount *fm,
+			      struct fuse_args *args)
+{
+	struct fuse_conn *fc = fm->fc;
+	int err = fuse_req_prep(fm, args, idmap);
+
+	if (err)
+		return err;
+
+	return fuse_chan_send(fc->chan, args);
+}
+
+int fuse_simple_background(struct fuse_mount *fm, struct fuse_args *args, gfp_t gfp_flags)
+{
+	struct fuse_conn *fc = fm->fc;
+	int err;
+
+	WARN_ON(args->force && !args->nocreds);
+
+	err = fuse_req_prep(fm, args, &invalid_mnt_idmap);
+	if (err)
+		return err;
+
+	return fuse_chan_send_bg(fc->chan, args, gfp_flags);
+}
+EXPORT_SYMBOL_GPL(fuse_simple_background);
+
+int fuse_simple_notify_reply(struct fuse_mount *fm, struct fuse_args *args, u64 unique)
+{
+	struct fuse_conn *fc = fm->fc;
+	int err;
+
+	WARN_ON(args->force && !args->nocreds);
+
+	err = fuse_req_prep(fm, args, &invalid_mnt_idmap);
+	if (err)
+		return err;
+
+	return fuse_chan_send_notify_reply(fc->chan, args, unique);
+}