File size seal for memory mapped region

When using memfd for cross process communication, we always need to seal
the file size, otherwise remote process and shrink the size we memory
mapped and thus crash the originate process causing a DoS

Bug: 294609150
Test: Build
Ignore-AOSP-First: security
(cherry picked from commit 3d9f1e3b0a135b784b9ffa0e65d6a699c7ed1f8e)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:77b758c59f58a05d1c0d45350796951bc778745f)
Merged-In: Ibc263c4f78df897e884378e3d984a188ca8772c7
Change-Id: Ibc263c4f78df897e884378e3d984a188ca8772c7

2 files changed, 11 insertions, 6 deletions

diff --git a/libs/binder/MemoryHeapBase.cpp b/libs/binder/MemoryHeapBase.cpp
index 8fe1d2bb3d..34e747ef21 100644
--- a/libs/binder/MemoryHeapBase.cpp
+++ b/libs/binder/MemoryHeapBase.cpp
@@ -73,8 +73,8 @@ MemoryHeapBase::MemoryHeapBase(size_t size, uint32_t flags, char const * name)
         ALOGV("MemoryHeapBase: Attempting to force MemFD");
         fd = memfd_create_region(name ? name : "MemoryHeapBase", size);
         if (fd < 0 || (mapfd(fd, true, size) != NO_ERROR)) return;
-        const int SEAL_FLAGS = ((mFlags & READ_ONLY) ? F_SEAL_FUTURE_WRITE : 0) |
-                ((mFlags & MEMFD_ALLOW_SEALING_FLAG) ? 0 : F_SEAL_SEAL);
+        const int SEAL_FLAGS = ((mFlags & READ_ONLY) ? F_SEAL_FUTURE_WRITE : 0) | F_SEAL_GROW |
+                F_SEAL_SHRINK | ((mFlags & MEMFD_ALLOW_SEALING_FLAG) ? 0 : F_SEAL_SEAL);
         if (SEAL_FLAGS && (fcntl(fd, F_ADD_SEALS, SEAL_FLAGS) == -1)) {
             ALOGE("MemoryHeapBase: MemFD %s sealing with flags %x failed with error  %s", name,
                   SEAL_FLAGS, strerror(errno));
diff --git a/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp b/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp
index 278dd2bf81..140270f5a1 100644
--- a/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp
+++ b/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp
@@ -37,7 +37,8 @@ TEST(MemoryHeapBase, MemfdSealed) {
     ASSERT_NE(mHeap.get(), nullptr);
     int fd = mHeap->getHeapID();
     EXPECT_NE(fd, -1);
-    EXPECT_EQ(fcntl(fd, F_GET_SEALS), F_SEAL_SEAL);
+    EXPECT_EQ(fcntl(fd, F_GET_SEALS), F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL);
+    EXPECT_EQ(ftruncate(fd, 4096), -1);
 }
 
 TEST(MemoryHeapBase, MemfdUnsealed) {
@@ -48,7 +49,8 @@ TEST(MemoryHeapBase, MemfdUnsealed) {
     ASSERT_NE(mHeap.get(), nullptr);
     int fd = mHeap->getHeapID();
     EXPECT_NE(fd, -1);
-    EXPECT_EQ(fcntl(fd, F_GET_SEALS), 0);
+    EXPECT_EQ(fcntl(fd, F_GET_SEALS), F_SEAL_GROW | F_SEAL_SHRINK);
+    EXPECT_EQ(ftruncate(fd, 4096), -1);
 }
 
 TEST(MemoryHeapBase, MemfdSealedProtected) {
@@ -59,7 +61,9 @@ TEST(MemoryHeapBase, MemfdSealedProtected) {
     ASSERT_NE(mHeap.get(), nullptr);
     int fd = mHeap->getHeapID();
     EXPECT_NE(fd, -1);
-    EXPECT_EQ(fcntl(fd, F_GET_SEALS), F_SEAL_SEAL | F_SEAL_FUTURE_WRITE);
+    EXPECT_EQ(fcntl(fd, F_GET_SEALS),
+              F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL | F_SEAL_FUTURE_WRITE);
+    EXPECT_EQ(ftruncate(fd, 4096), -1);
 }
 
 TEST(MemoryHeapBase, MemfdUnsealedProtected) {
@@ -71,7 +75,8 @@ TEST(MemoryHeapBase, MemfdUnsealedProtected) {
     ASSERT_NE(mHeap.get(), nullptr);
     int fd = mHeap->getHeapID();
     EXPECT_NE(fd, -1);
-    EXPECT_EQ(fcntl(fd, F_GET_SEALS), F_SEAL_FUTURE_WRITE);
+    EXPECT_EQ(fcntl(fd, F_GET_SEALS), F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_FUTURE_WRITE);
+    EXPECT_EQ(ftruncate(fd, 4096), -1);
 }
 
 #else