usercopy: Adjust tests to deal with SMAP/PAN

commit f5f893c57e37ca730808cb2eee3820abd05e7507 upstream.

Under SMAP/PAN/etc, we cannot write directly to userspace memory, so
this rearranges the test bytes to get written through copy_to_user().
Additionally drops the bad copy_from_user() test that would trigger a
memcpy() against userspace on failure.

[arnd: the test module was added in 3.14, and this backported patch
       should apply cleanly on all version from 3.14 to 4.10.
       The original patch was in 4.11 on top of a context change
       I saw the bug triggered with kselftest on a 4.4.y stable kernel]

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index 0ecef3e..5e6db6b 100644 (file)
--- a/lib/test_user_copy.c
+++ b/lib/test_user_copy.c
@@ -58,7 +58,9 @@ static int __init test_user_copy_init(void)
        usermem = (char __user *)user_addr;
        bad_usermem = (char *)user_addr;
 
-       /* Legitimate usage: none of these should fail. */
+       /*
+        * Legitimate usage: none of these copies should fail.
+        */
        ret |= test(copy_from_user(kmem, usermem, PAGE_SIZE),
                    "legitimate copy_from_user failed");
        ret |= test(copy_to_user(usermem, kmem, PAGE_SIZE),
@@ -68,19 +70,33 @@ static int __init test_user_copy_init(void)
        ret |= test(put_user(value, (unsigned long __user *)usermem),
                    "legitimate put_user failed");
 
-       /* Invalid usage: none of these should succeed. */
+       /*
+        * Invalid usage: none of these copies should succeed.
+        */
+
+       /* Reject kernel-to-kernel copies through copy_from_user(). */
        ret |= test(!copy_from_user(kmem, (char __user *)(kmem + PAGE_SIZE),
                                    PAGE_SIZE),
                    "illegal all-kernel copy_from_user passed");
+
+#if 0
+       /*
+        * When running with SMAP/PAN/etc, this will Oops the kernel
+        * due to the zeroing of userspace memory on failure. This needs
+        * to be tested in LKDTM instead, since this test module does not
+        * expect to explode.
+        */
        ret |= test(!copy_from_user(bad_usermem, (char __user *)kmem,
                                    PAGE_SIZE),
                    "illegal reversed copy_from_user passed");
+#endif
        ret |= test(!copy_to_user((char __user *)kmem, kmem + PAGE_SIZE,
                                  PAGE_SIZE),
                    "illegal all-kernel copy_to_user passed");
        ret |= test(!copy_to_user((char __user *)kmem, bad_usermem,
                                  PAGE_SIZE),
                    "illegal reversed copy_to_user passed");
+
        ret |= test(!get_user(value, (unsigned long __user *)kmem),
                    "illegal get_user passed");
        ret |= test(!put_user(value, (unsigned long __user *)kmem),