[edk2-devel] [PATCH v1 1/2] FatPkg/EnhancedFatDxe: Fix SIGN_EXTENSION Coverity issues

["Ranbir Singh" <rsingh@ventanamicro.com>]

From: Ranbir Singh <Ranbir.Singh3@Dell.com>

The functions FatGetDirEntInfo and FatOpenDirEnt contains the code
statements

      Cluster            = (Entry->FileClusterHigh << 16) | Entry->FileCluster;
      and
      OFile->FileCluster = ((DirEnt->Entry.FileClusterHigh) << 16) | (DirEnt->Entry.FileCluster);

respectively. As per Coverity report, in both these statements, there is
an "Operand1" with type "UINT16" (16 bits, unsigned) which is promoted in
"(Operand1 << 16) | Operand2" to type "int" (32 bits, signed), then sign-
extended to type "unsigned long long" (64 bits, unsigned). If the result
of "(Operand1 << 16) | Operand2" is greater than 0x7FFFFFFF, the upper
bits of the result will all be 1.

So to avoid sign-extension, typecast the Operand1 and then the inter-
-mediate result after << 16 operation with UINTN. Note - UINTN is the
data type of the variable on the LHS of the assignment.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4249

Cc: Ray Ni <ray.ni@intel.com>
Co-authored-by: Veeresh Sangolli <veeresh.sangolli@dellteam.com>
Signed-off-by: Ranbir Singh <Ranbir.Singh3@Dell.com>
Signed-off-by: Ranbir Singh <rsingh@ventanamicro.com>
---
 FatPkg/EnhancedFatDxe/DirectoryManage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/FatPkg/EnhancedFatDxe/DirectoryManage.c b/FatPkg/EnhancedFatDxe/DirectoryManage.c
index 723fc35f38db..a21b7973cd21 100644
--- a/FatPkg/EnhancedFatDxe/DirectoryManage.c
+++ b/FatPkg/EnhancedFatDxe/DirectoryManage.c
@@ -474,7 +474,7 @@ FatGetDirEntInfo (
     Info       = Buffer;
     Info->Size = ResultSize;
     if ((Entry->Attributes & FAT_ATTRIBUTE_DIRECTORY) != 0) {
-      Cluster            = (Entry->FileClusterHigh << 16) | Entry->FileCluster;
+      Cluster            = (UINTN)((UINTN)(Entry->FileClusterHigh) << 16) | Entry->FileCluster;
       Info->PhysicalSize = FatPhysicalDirSize (Volume, Cluster);
       Info->FileSize     = Info->PhysicalSize;
     } else {
@@ -1167,7 +1167,7 @@ FatOpenDirEnt (
       //
       Volume             = Parent->Volume;
       OFile->FullPathLen = Parent->FullPathLen + 1 + StrLen (DirEnt->FileString);
-      OFile->FileCluster = ((DirEnt->Entry.FileClusterHigh) << 16) | (DirEnt->Entry.FileCluster);
+      OFile->FileCluster = (UINTN)((UINTN)(DirEnt->Entry.FileClusterHigh) << 16) | (DirEnt->Entry.FileCluster);
       InsertTailList (&Parent->ChildHead, &OFile->ChildLink);
     } else {
       //
-- 
2.34.1



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