[edk2-platforms][PATCH v4 06/12] Ext4Pkg: Corrects integer overflow check logic in DiskUtil

["Savva Mitrofanov" <savvamtr@gmail.com>]

Corrects multiplication overflow check code and adds additional check
for emptiness of number of blocks and block number

Cc: Marvin Häuser <mhaeuser@posteo.de>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Vitaly Cheptsov <vit9696@protonmail.com>
Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
---
 Features/Ext4Pkg/Ext4Pkg.dsc        |  2 +-
 Features/Ext4Pkg/Ext4Dxe/DiskUtil.c | 18 ++++++++++++++----
 Features/Ext4Pkg/Ext4Dxe/Extents.c  | 15 ++++++++++++---
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/Features/Ext4Pkg/Ext4Pkg.dsc b/Features/Ext4Pkg/Ext4Pkg.dsc
index 59bc327ebf6e..621c63eaf92d 100644
--- a/Features/Ext4Pkg/Ext4Pkg.dsc
+++ b/Features/Ext4Pkg/Ext4Pkg.dsc
@@ -46,7 +46,7 @@
   DevicePathLib|MdePkg/Library/UefiDevicePathLib/UefiDevicePathLib.inf
   OrderedCollectionLib|MdePkg/Library/BaseOrderedCollectionRedBlackTreeLib/BaseOrderedCollectionRedBlackTreeLib.inf
   BaseUcs2Utf8Lib|RedfishPkg/Library/BaseUcs2Utf8Lib/BaseUcs2Utf8Lib.inf
-  
+
   #
   # Required for stack protector support
   #
diff --git a/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c b/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
index 32da35f7d9f5..5df9ce5bafcf 100644
--- a/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
+++ b/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
@@ -54,17 +54,20 @@ Ext4ReadBlocks (
   UINT64  Offset;
   UINTN   Length;
 
+  ASSERT (NumberBlocks != 0);
+  ASSERT (BlockNumber != EXT4_BLOCK_FILE_HOLE);
+
   Offset = MultU64x32 (BlockNumber, Partition->BlockSize);
   Length = NumberBlocks * Partition->BlockSize;
 
   // Check for overflow on the block -> byte conversions.
   // Partition->BlockSize is never 0, so we don't need to check for that.
 
-  if (Offset > DivU64x32 ((UINT64)-1, Partition->BlockSize)) {
+  if (DivU64x64Remainder (Offset, BlockNumber, NULL) != Partition->BlockSize) {
     return EFI_INVALID_PARAMETER;
   }
 
-  if (Length > (UINTN)-1/Partition->BlockSize) {
+  if (Length / NumberBlocks != Partition->BlockSize) {
     return EFI_INVALID_PARAMETER;
   }
 
@@ -92,14 +95,21 @@ Ext4AllocAndReadBlocks (
   VOID   *Buf;
   UINTN  Length;
 
+  // Check that number of blocks isn't empty, because
+  // this is incorrect condition for opened partition,
+  // so we just early-exit
+  if ((NumberBlocks == 0) || (BlockNumber == EXT4_BLOCK_FILE_HOLE)) {
+    return NULL;
+  }
+
   Length = NumberBlocks * Partition->BlockSize;
 
-  if (Length > (UINTN)-1/Partition->BlockSize) {
+  // Check for integer overflow
+  if (Length / NumberBlocks != Partition->BlockSize) {
     return NULL;
   }
 
   Buf = AllocatePool (Length);
-
   if (Buf == NULL) {
     return NULL;
   }
diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c b/Features/Ext4Pkg/Ext4Dxe/Extents.c
index e1001d0a4292..99cb0f204fc2 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
@@ -237,6 +237,7 @@ Ext4GetExtent (
   EXT4_EXTENT_HEADER  *ExtHeader;
   EXT4_EXTENT_INDEX   *Index;
   EFI_STATUS          Status;
+  EXT4_BLOCK_NR       BlockNumber;
 
   Inode  = File->Inode;
   Ext    = NULL;
@@ -288,7 +289,16 @@ Ext4GetExtent (
     // Therefore, we can use binary search, and it's actually the standard for doing so
     // (see FreeBSD).
 
-    Index = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
+    Index       = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
+    BlockNumber = Ext4ExtentIdxLeafBlock (Index);
+
+    // Check that block isn't file hole
+    if (BlockNumber == EXT4_BLOCK_FILE_HOLE) {
+      if (Buffer != NULL) {
+        FreePool (Buffer);
+      }
+      return EFI_NO_MAPPING;
+    }
 
     if (Buffer == NULL) {
       Buffer = AllocatePool (Partition->BlockSize);
@@ -298,8 +308,7 @@ Ext4GetExtent (
     }
 
     // Read the leaf block onto the previously-allocated buffer.
-
-    Status = Ext4ReadBlocks (Partition, Buffer, 1, Ext4ExtentIdxLeafBlock (Index));
+    Status = Ext4ReadBlocks (Partition, Buffer, 1, BlockNumber);
     if (EFI_ERROR (Status)) {
       FreePool (Buffer);
       return Status;
-- 
2.39.1