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, 75 insertions, 0 deletions

diff --git a/Documentation/filesystems/dnotify.rst b/Documentation/filesystems/dnotify.rst
new file mode 100644
index 000000000..a28a1f9ef
--- /dev/null
+++ b/Documentation/filesystems/dnotify.rst
@@ -0,0 +1,75 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+Linux Directory Notification
+============================
+
+	   Stephen Rothwell <sfr@canb.auug.org.au>
+
+The intention of directory notification is to allow user applications
+to be notified when a directory, or any of the files in it, are changed.
+The basic mechanism involves the application registering for notification
+on a directory using a fcntl(2) call and the notifications themselves
+being delivered using signals.
+
+The application decides which "events" it wants to be notified about.
+The currently defined events are:
+
+	=========	=====================================================
+	DN_ACCESS	A file in the directory was accessed (read)
+	DN_MODIFY	A file in the directory was modified (write,truncate)
+	DN_CREATE	A file was created in the directory
+	DN_DELETE	A file was unlinked from directory
+	DN_RENAME	A file in the directory was renamed
+	DN_ATTRIB	A file in the directory had its attributes
+			changed (chmod,chown)
+	=========	=====================================================
+
+Usually, the application must reregister after each notification, but
+if DN_MULTISHOT is or'ed with the event mask, then the registration will
+remain until explicitly removed (by registering for no events).
+
+By default, SIGIO will be delivered to the process and no other useful
+information.  However, if the F_SETSIG fcntl(2) call is used to let the
+kernel know which signal to deliver, a siginfo structure will be passed to
+the signal handler and the si_fd member of that structure will contain the
+file descriptor associated with the directory in which the event occurred.
+
+Preferably the application will choose one of the real time signals
+(SIGRTMIN + <n>) so that the notifications may be queued.  This is
+especially important if DN_MULTISHOT is specified.  Note that SIGRTMIN
+is often blocked, so it is better to use (at least) SIGRTMIN + 1.
+
+Implementation expectations (features and bugs :-))
+---------------------------------------------------
+
+The notification should work for any local access to files even if the
+actual file system is on a remote server.  This implies that remote
+access to files served by local user mode servers should be notified.
+Also, remote accesses to files served by a local kernel NFS server should
+be notified.
+
+In order to make the impact on the file system code as small as possible,
+the problem of hard links to files has been ignored.  So if a file (x)
+exists in two directories (a and b) then a change to the file using the
+name "a/x" should be notified to a program expecting notifications on
+directory "a", but will not be notified to one expecting notifications on
+directory "b".
+
+Also, files that are unlinked, will still cause notifications in the
+last directory that they were linked to.
+
+Configuration
+-------------
+
+Dnotify is controlled via the CONFIG_DNOTIFY configuration option.  When
+disabled, fcntl(fd, F_NOTIFY, ...) will return -EINVAL.
+
+Example
+-------
+See tools/testing/selftests/filesystems/dnotify_test.c for an example.
+
+NOTE
+----
+Beginning with Linux 2.6.13, dnotify has been replaced by inotify.
+See Documentation/filesystems/inotify.rst for more information on it.