commit 3d9f1e3b0a135b784b9ffa0e65d6a699c7ed1f8e
author Keith Mok <keithmok@google.com> Fri Aug 04 22:17:08 2023 +0000
committer Keith Mok <keithmok@google.com> Fri Aug 11 21:40:23 2023 +0000
tree f33c337d1419118b34a13b1304d0b9b67feff061
parent 47f61c48649af99bb245e4faea08788b76b4347d

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
Change-Id: Ibc263c4f78df897e884378e3d984a188ca8772c7

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