shmat() for 0 (or <PAGESIZE with RND flag) has to fail with REMAPs

From: Rafael David Tinoco <[email protected]>

Fixes https://github.com/linux-test-project/ltp/issues/319

According to upstream thread (https://lkml.org/lkml/2018/5/28/2056),
cve-2017-5669 needs to address the "new" way of handling nil addresses for shmat() when used with MAP_FIXED or SHM_REMAP flags.

- mapping nil-page is OK on lower addresses with MAP_FIXED (or else X11 is broken)
- mapping nil-page is NOT OK with SHM_REMAP on lower addresses

Addresses Davidlohr Bueso's comments/changes:

commit 8f89c007b6de

Author: Davidlohr Bueso <[email protected]>
Date:   Fri May 25 14:47:30 2018 -0700

ipc/shm: fix shmat() nil address after round-down when remapping

commit a73ab244f0da

Author: Davidlohr Bueso <[email protected]>
Date:   Fri May 25 14:47:27 2018 -0700

Revert "ipc/shm: Fix shmat mmap nil-page protection"

For previously test made based on:

commit 95e91b831f87

Author: Davidlohr Bueso <[email protected]>
Date:   Mon Feb 27 14:28:24 2017 -0800

ipc/shm: Fix shmat mmap nil-page protection

Signed-off-by Rafael David Tinoco <[email protected]>

---
testcases/cve/cve-2017-5669.c | 9 ++++++++-

1 file changed, 8 insertions(+), 1 deletion(-)

testcases/cve/cve-2017-5669.c +8 -1

index 1ca598326..16e4d80be 100644
@@ -28,6 +28,9 @@
 * is just to see if we get an access error or some other unexpected behaviour.
 *
 * See commit 95e91b831f (ipc/shm: Fix shmat mmap nil-page protection)
+ * See commit a73ab244f0da (Revert "ipc/shm: Fix shmat mmap nil-page protect...)
+ * See commit 8f89c007b6de (ipc/shm: fix shmat() nil address after round-dow...)
+ * See https://github.com/linux-test-project/ltp/issues/319
 */
 #include <sys/types.h>
 #include <sys/ipc.h>

@@ -60,7 +63,11 @@ static void cleanup(void)
 static void run(void)
 {
 	tst_res(TINFO, "Attempting to attach shared memory to null page");
-	shm_addr = shmat(shm_id, ((void *)1), SHM_RND);
+	/*
+	 * shmat() for 0 (or < PAGESIZE with RND flag) has to fail with REMAPs
+	 * https://github.com/linux-test-project/ltp/issues/319
+	 */
+	shm_addr = shmat(shm_id, ((void *)1), SHM_RND | SHM_REMAP);
 	if (shm_addr == (void *)-1) {
 		shm_addr = NULL;
 		if (errno == EINVAL) {

Signature · 1 line

2.17.1

From: Rafael David Tinoco <[email protected]>

Fixes https://github.com/linux-test-project/ltp/issues/319