[PATCH] FatPkg/EnhancedFatDxe: Fix various Coverity issues

[PATCH] FatPkg/EnhancedFatDxe: Fix various Coverity issues

[Ranbir Singh]

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The functions FatGetDirEntInfo and FatOpenDirEnt in the file
FatPkg/EnhancedFatDxe/DirectoryManage.c contains the code statements

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

respectively. In both these statements, there is an "Operand1" with
type "UINT16" (16 bits, unsigned) which is promoted in the operation
"(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 "Operand1" with UINTN which is the data type of the variable
on the LHS of the assignment.

The function FatInitializeDiskCache in the file
FatPkg/EnhancedFatDxe/DiskCache.c evaluates an expression

FAT_DATACACHE_GROUP_COUNT << DiskCache[CacheData].PageAlignment
and
assigns it to DataCacheSize which is of type UINTN;

As per Coverity report,
FAT_DATACACHE_GROUP_COUNT << DiskCache[CacheData].PageAlignment is a
potentially overflowing expression with type "int" (32 bits, signed)
evaluated using 32-bit arithmetic, and then used in a context that
expects an expression of type "UINTN" (64 bits, unsigned).
To avoid overflow, cast "FAT_DATACACHE_GROUP_COUNT" to type "UINTN".

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4249
Signed-off-by: Ranbir Singh <Ranbir.Singh3@Dell.com>
---
FatPkg/EnhancedFatDxe/DirectoryManage.c | 4 ++--
FatPkg/EnhancedFatDxe/DiskCache.c       | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/FatPkg/EnhancedFatDxe/DirectoryManage.c b/FatPkg/EnhancedFatDxe/DirectoryManage.c
index 723fc35f38..cdae864be0 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)(Entry->FileClusterHigh) << 16) | (UINTN)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)(DirEnt->Entry.FileClusterHigh) << 16) | (DirEnt->Entry.FileCluster);
InsertTailList (&Parent->ChildHead, &OFile->ChildLink);
} else {
//
diff --git a/FatPkg/EnhancedFatDxe/DiskCache.c b/FatPkg/EnhancedFatDxe/DiskCache.c
index d1a34a6a64..d56e338586 100644
--- a/FatPkg/EnhancedFatDxe/DiskCache.c
+++ b/FatPkg/EnhancedFatDxe/DiskCache.c
@@ -477,7 +477,7 @@ FatInitializeDiskCache (
DiskCache[CacheFat].BaseAddress   = Volume->FatPos;
DiskCache[CacheFat].LimitAddress  = Volume->FatPos + Volume->FatSize;
FatCacheSize                      = FatCacheGroupCount << DiskCache[CacheFat].PageAlignment;
-  DataCacheSize                     = FAT_DATACACHE_GROUP_COUNT << DiskCache[CacheData].PageAlignment;
+  DataCacheSize                     = (UINTN)FAT_DATACACHE_GROUP_COUNT << DiskCache[CacheData].PageAlignment;
//
// Allocate the Fat Cache buffer
//
--
2.36.1.windows.1

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