liblp: Add integer overflow checks when aligning.

This will prevent ubsan crashes on invalid inputs.

Bug: 155510366
Test: liblp_test gtest
Change-Id: Id6dd8badd0025d6cac3113c3f9076ea3f4d9c175

fs_mgr/liblp/builder.cpp

@@ -19,6 +19,7 @@
 #include <string.h>
 
 #include <algorithm>
+#include <limits>
 
 #include <android-base/unique_fd.h>
 
@@ -369,7 +370,10 @@ bool MetadataBuilder::Init(const std::vector<BlockDeviceInfo>& block_devices,
     }
 
     // Align the metadata size up to the nearest sector.
-    metadata_max_size = AlignTo(metadata_max_size, LP_SECTOR_SIZE);
+    if (!AlignTo(metadata_max_size, LP_SECTOR_SIZE, &metadata_max_size)) {
+        LERROR << "Max metadata size " << metadata_max_size << " is too large.";
+        return false;
+    }
 
     // Validate and build the block device list.
     uint32_t logical_block_size = 0;
@@ -401,10 +405,15 @@ bool MetadataBuilder::Init(const std::vector<BlockDeviceInfo>& block_devices,
         // untouched to be compatible code that looks for an MBR. Thus we
         // start counting free sectors at sector 1, not 0.
         uint64_t free_area_start = LP_SECTOR_SIZE;
+        bool ok;
         if (out.alignment) {
-            free_area_start = AlignTo(free_area_start, out.alignment);
+            ok = AlignTo(free_area_start, out.alignment, &free_area_start);
         } else {
-            free_area_start = AlignTo(free_area_start, logical_block_size);
+            ok = AlignTo(free_area_start, logical_block_size, &free_area_start);
+        }
+        if (!ok) {
+            LERROR << "Integer overflow computing free area start";
+            return false;
         }
         out.first_logical_sector = free_area_start / LP_SECTOR_SIZE;
 
@@ -441,10 +450,15 @@ bool MetadataBuilder::Init(const std::vector<BlockDeviceInfo>& block_devices,
 
     // Compute the first free sector, factoring in alignment.
     uint64_t free_area_start = total_reserved;
+    bool ok;
     if (super.alignment || super.alignment_offset) {
-        free_area_start = AlignTo(free_area_start, super.alignment);
+        ok = AlignTo(free_area_start, super.alignment, &free_area_start);
     } else {
-        free_area_start = AlignTo(free_area_start, logical_block_size);
+        ok = AlignTo(free_area_start, logical_block_size, &free_area_start);
+    }
+    if (!ok) {
+        LERROR << "Integer overflow computing free area start";
+        return false;
     }
     super.first_logical_sector = free_area_start / LP_SECTOR_SIZE;
 
@@ -544,7 +558,11 @@ void MetadataBuilder::ExtentsToFreeList(const std::vector<Interval>& extents,
         const Interval& current = extents[i];
         DCHECK(previous.device_index == current.device_index);
 
-        uint64_t aligned = AlignSector(block_devices_[current.device_index], previous.end);
+        uint64_t aligned;
+        if (!AlignSector(block_devices_[current.device_index], previous.end, &aligned)) {
+            LERROR << "Sector " << previous.end << " caused integer overflow.";
+            continue;
+        }
         if (aligned >= current.start) {
             // There is no gap between these two extents, try the next one.
             // Note that we check with >= instead of >, since alignment may
@@ -730,7 +748,10 @@ std::vector<Interval> MetadataBuilder::PrioritizeSecondHalfOfSuper(
     // Choose an aligned sector for the midpoint. This could lead to one half
     // being slightly larger than the other, but this will not restrict the
     // size of partitions (it might lead to one extra extent if "B" overflows).
-    midpoint = AlignSector(super, midpoint);
+    if (!AlignSector(super, midpoint, &midpoint)) {
+        LERROR << "Unexpected integer overflow aligning midpoint " << midpoint;
+        return free_list;
+    }
 
     std::vector<Interval> first_half;
     std::vector<Interval> second_half;
@@ -768,7 +789,11 @@ std::unique_ptr<LinearExtent> MetadataBuilder::ExtendFinalExtent(
     // If the sector ends where the next aligned chunk begins, then there's
     // no missing gap to try and allocate.
     const auto& block_device = block_devices_[extent->device_index()];
-    uint64_t next_aligned_sector = AlignSector(block_device, extent->end_sector());
+    uint64_t next_aligned_sector;
+    if (!AlignSector(block_device, extent->end_sector(), &next_aligned_sector)) {
+        LERROR << "Integer overflow aligning sector " << extent->end_sector();
+        return nullptr;
+    }
     if (extent->end_sector() == next_aligned_sector) {
         return nullptr;
     }
@@ -925,13 +950,19 @@ uint64_t MetadataBuilder::UsedSpace() const {
     return size;
 }
 
-uint64_t MetadataBuilder::AlignSector(const LpMetadataBlockDevice& block_device,
-                                      uint64_t sector) const {
+bool MetadataBuilder::AlignSector(const LpMetadataBlockDevice& block_device, uint64_t sector,
+                                  uint64_t* out) const {
     // Note: when reading alignment info from the Kernel, we don't assume it
     // is aligned to the sector size, so we round up to the nearest sector.
     uint64_t lba = sector * LP_SECTOR_SIZE;
-    uint64_t aligned = AlignTo(lba, block_device.alignment);
-    return AlignTo(aligned, LP_SECTOR_SIZE) / LP_SECTOR_SIZE;
+    if (!AlignTo(lba, block_device.alignment, out)) {
+        return false;
+    }
+    if (!AlignTo(*out, LP_SECTOR_SIZE, out)) {
+        return false;
+    }
+    *out /= LP_SECTOR_SIZE;
+    return true;
 }
 
 bool MetadataBuilder::FindBlockDeviceByName(const std::string& partition_name,
@@ -1005,7 +1036,12 @@ bool MetadataBuilder::UpdateBlockDeviceInfo(size_t index, const BlockDeviceInfo&
 bool MetadataBuilder::ResizePartition(Partition* partition, uint64_t requested_size,
                                       const std::vector<Interval>& free_region_hint) {
     // Align the space needed up to the nearest sector.
-    uint64_t aligned_size = AlignTo(requested_size, geometry_.logical_block_size);
+    uint64_t aligned_size;
+    if (!AlignTo(requested_size, geometry_.logical_block_size, &aligned_size)) {
+        LERROR << "Cannot resize partition " << partition->name() << " to " << requested_size
+               << " bytes; integer overflow.";
+        return false;
+    }
     uint64_t old_size = partition->size();
 
     if (!ValidatePartitionSizeChange(partition, old_size, aligned_size, false)) {

fs_mgr/liblp/builder_test.cpp

@@ -228,8 +228,9 @@ TEST_F(BuilderTest, InternalPartitionAlignment) {
         ASSERT_EQ(extent.target_type, LP_TARGET_TYPE_LINEAR);
         EXPECT_EQ(extent.num_sectors, 80);
 
+        uint64_t aligned_lba;
         uint64_t lba = extent.target_data * LP_SECTOR_SIZE;
-        uint64_t aligned_lba = AlignTo(lba, device_info.alignment);
+        ASSERT_TRUE(AlignTo(lba, device_info.alignment, &aligned_lba));
         EXPECT_EQ(lba, aligned_lba);
     }
 
@@ -1051,3 +1052,17 @@ TEST_F(BuilderTest, AlignFreeRegion) {
     EXPECT_EQ(e2->physical_sector(), 3072);
     EXPECT_EQ(e2->end_sector(), 4197368);
 }
+
+TEST_F(BuilderTest, ResizeOverflow) {
+    BlockDeviceInfo super("super", 8_GiB, 786432, 229376, 4096);
+    std::vector<BlockDeviceInfo> block_devices = {super};
+
+    unique_ptr<MetadataBuilder> builder = MetadataBuilder::New(block_devices, "super", 65536, 2);
+    ASSERT_NE(builder, nullptr);
+
+    ASSERT_TRUE(builder->AddGroup("group", 0));
+
+    Partition* p = builder->AddPartition("system", "default", 0);
+    ASSERT_NE(p, nullptr);
+    ASSERT_FALSE(builder->ResizePartition(p, 18446744073709551615ULL));
+}

fs_mgr/liblp/include/liblp/builder.h

@@ -359,7 +359,7 @@ class MetadataBuilder {
     bool GrowPartition(Partition* partition, uint64_t aligned_size,
                        const std::vector<Interval>& free_region_hint);
     void ShrinkPartition(Partition* partition, uint64_t aligned_size);
-    uint64_t AlignSector(const LpMetadataBlockDevice& device, uint64_t sector) const;
+    bool AlignSector(const LpMetadataBlockDevice& device, uint64_t sector, uint64_t* out) const;
     uint64_t TotalSizeOfGroup(PartitionGroup* group) const;
     bool UpdateBlockDeviceInfo(size_t index, const BlockDeviceInfo& info);
     bool FindBlockDeviceByName(const std::string& partition_name, uint32_t* index) const;

fs_mgr/liblp/utility.h

@@ -21,6 +21,7 @@
 #include <stdint.h>
 #include <sys/types.h>
 
+#include <limits>
 #include <string>
 #include <string_view>
 
@@ -66,16 +67,26 @@ int64_t SeekFile64(int fd, int64_t offset, int whence);
 void SHA256(const void* data, size_t length, uint8_t out[32]);
 
 // Align |base| such that it is evenly divisible by |alignment|, which does not
-// have to be a power of two.
-constexpr uint64_t AlignTo(uint64_t base, uint32_t alignment) {
+// have to be a power of two. Return false on overflow.
+template <typename T>
+bool AlignTo(T base, uint32_t alignment, T* out) {
+    static_assert(std::numeric_limits<T>::is_integer);
+    static_assert(!std::numeric_limits<T>::is_signed);
     if (!alignment) {
-        return base;
+        *out = base;
+        return true;
     }
-    uint64_t remainder = base % alignment;
+    T remainder = base % alignment;
     if (remainder == 0) {
-        return base;
+        *out = base;
+        return true;
     }
-    return base + (alignment - remainder);
+    T to_add = alignment - remainder;
+    if (to_add > std::numeric_limits<T>::max() - base) {
+        return false;
+    }
+    *out = base + to_add;
+    return true;
 }
 
 // Update names from C++ strings.

fs_mgr/liblp/utility_test.cpp

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include <optional>
+
 #include <gtest/gtest.h>
 #include <liblp/builder.h>
 #include <liblp/liblp.h>
@@ -58,15 +60,28 @@ TEST(liblp, GetMetadataOffset) {
     EXPECT_EQ(GetBackupMetadataOffset(geometry, 0), backup_start + 16384 * 0);
 }
 
+std::optional<uint64_t> AlignTo(uint64_t base, uint32_t alignment) {
+    uint64_t r;
+    if (!AlignTo(base, alignment, &r)) {
+        return {};
+    }
+    return {r};
+}
+
 TEST(liblp, AlignTo) {
-    EXPECT_EQ(AlignTo(37, 0), 37);
-    EXPECT_EQ(AlignTo(1024, 1024), 1024);
-    EXPECT_EQ(AlignTo(555, 1024), 1024);
-    EXPECT_EQ(AlignTo(555, 1000), 1000);
-    EXPECT_EQ(AlignTo(0, 1024), 0);
-    EXPECT_EQ(AlignTo(54, 32), 64);
-    EXPECT_EQ(AlignTo(32, 32), 32);
-    EXPECT_EQ(AlignTo(17, 32), 32);
+    EXPECT_EQ(AlignTo(37, 0), std::optional<uint64_t>(37));
+    EXPECT_EQ(AlignTo(1024, 1024), std::optional<uint64_t>(1024));
+    EXPECT_EQ(AlignTo(555, 1024), std::optional<uint64_t>(1024));
+    EXPECT_EQ(AlignTo(555, 1000), std::optional<uint64_t>(1000));
+    EXPECT_EQ(AlignTo(0, 1024), std::optional<uint64_t>(0));
+    EXPECT_EQ(AlignTo(54, 32), std::optional<uint64_t>(64));
+    EXPECT_EQ(AlignTo(32, 32), std::optional<uint64_t>(32));
+    EXPECT_EQ(AlignTo(17, 32), std::optional<uint64_t>(32));
+
+    auto u32limit = std::numeric_limits<uint32_t>::max();
+    auto u64limit = std::numeric_limits<uint64_t>::max();
+    EXPECT_EQ(AlignTo(u64limit - u32limit + 1, u32limit), std::optional<uint64_t>{u64limit});
+    EXPECT_EQ(AlignTo(std::numeric_limits<uint64_t>::max(), 2), std::optional<uint64_t>{});
 }
 
 TEST(liblp, GetPartitionSlotSuffix) {