commit aa98edf0ce9dde4886979658a459900ca987f193
author Keith Mok <keithmok@google.com> Fri Aug 04 22:17:08 2023 +0000
committer Android Build Coastguard Worker <android-build-coastguard-worker@google.com> Wed Dec 06 22:44:29 2023 +0000
tree f963f8f8ac41178e35e1aa54d150676028832a25
parent bfcf75076e562945bae131a4929f29a90d0d2481

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

libs/binder/MemoryHeapBase.cpp

diff --git a/libs/binder/MemoryHeapBase.cpp b/libs/binder/MemoryHeapBase.cpp
index 8fe1d2b..34e747e 100644
--- a/libs/binder/MemoryHeapBase.cpp
+++ b/libs/binder/MemoryHeapBase.cpp
@@ -73,8 +73,8 @@
         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));

libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp

diff --git a/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp b/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp
index 278dd2b..140270f 100644
--- a/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp
+++ b/libs/binder/tests/binderMemoryHeapBaseUnitTest.cpp
@@ -37,7 +37,8 @@
     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 @@
     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 @@
     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 @@
     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