ShellPkg/Shell: eliminate double-free in RunSplitCommand()

Commit bd3fc81 ("ShellPkg/App: Fix memory leak and save resources.",
2016-05-20) added a FreePool() call for Split->SplitStdIn, near end of the
RunSplitCommand(), right after the same shell file was closed with
CloseFile(). The argument was:

> 1) RunSplitCommand() allocates the initial SplitStdOut via
>    CreateFileInterfaceMem(). Free SplitStdIn after the swap to fix
>    the memory leak.

There is no memory leak actually, and the FreePool() call in question
constitutes a double-free:

(a) This is how the handle is established:

    ConvertEfiFileProtocolToShellHandle (
      CreateFileInterfaceMem (Unicode),
      NULL
      );

    CreateFileInterfaceMem() allocates an EFI_FILE_PROTOCOL_MEM object and
    populates it fully. ConvertEfiFileProtocolToShellHandle() allocates
    some administrative structures and links the EFI_FILE_PROTOCOL_MEM
    object into "mFileHandleList".

(b) EFI_SHELL_PROTOCOL.CloseFile() is required to close the
    SHELL_FILE_HANDLE and to release all associated data. Accordingly,
    near the end of RunSplitCommand(), we have:

    EfiShellClose()
      ShellFileHandleRemove()
        //
        // undoes the effects of ConvertEfiFileProtocolToShellHandle()
        //
      ConvertShellHandleToEfiFileProtocol()
        //
        // note that this does not adjust the pointer value; it's a pure
        // type cast
        //
      FileHandleClose()
        FileInterfaceMemClose()
          //
          // tears down EFI_FILE_PROTOCOL_MEM completely, undoing the
          // effects of CreateFileInterfaceMem ()
          //

The FreePool() call added by bd3fc81 conflicts with

  SHELL_FREE_NON_NULL(This);

in FileInterfaceMemClose(), so remove it.

This error can be reproduced for example with:

> Shell> map | more
> 'more' is not recognized as an internal or external command, operable
> program, or script file.

which triggers:

> ASSERT MdeModulePkg/Core/Dxe/Mem/Pool.c(624): CR has Bad Signature

with the following stack dump:

> #0  0x000000007f6dc094 in CpuDeadLoop () at
>     MdePkg/Library/BaseLib/CpuDeadLoop.c:37
> #1  0x000000007f6dd1b4 in DebugAssert (FileName=0x7f6ed9f0
>     "MdeModulePkg/Core/Dxe/Mem/Pool.c", LineNumber=624,
>     Description=0x7f6ed9d8 "CR has Bad Signature") at
>     OvmfPkg/Library/PlatformDebugLibIoPort/DebugLib.c:153
> #2  0x000000007f6d075d in CoreFreePoolI (Buffer=0x7e232c98,
>     PoolType=0x7f6bc1c4) at MdeModulePkg/Core/Dxe/Mem/Pool.c:624
> tianocore#3  0x000000007f6d060e in CoreInternalFreePool (Buffer=0x7e232c98,
>     PoolType=0x7f6bc1c4) at MdeModulePkg/Core/Dxe/Mem/Pool.c:529
> tianocore#4  0x000000007f6d0648 in CoreFreePool (Buffer=0x7e232c98) at
>     MdeModulePkg/Core/Dxe/Mem/Pool.c:552
> tianocore#5  0x000000007d49fbf8 in FreePool (Buffer=0x7e232c98) at
>     MdePkg/Library/UefiMemoryAllocationLib/MemoryAllocationLib.c:818
> tianocore#6  0x000000007d4875c3 in RunSplitCommand (CmdLine=0x7d898398,
>     StdIn=0x0, StdOut=0x0) at ShellPkg/Application/Shell/Shell.c:1813
> tianocore#7  0x000000007d487d59 in ProcessNewSplitCommandLine
>     (CmdLine=0x7d898398) at ShellPkg/Application/Shell/Shell.c:2121
> tianocore#8  0x000000007d488937 in RunShellCommand (CmdLine=0x7e233018,
>     CommandStatus=0x0) at ShellPkg/Application/Shell/Shell.c:2670
> tianocore#9  0x000000007d488b0b in RunCommand (CmdLine=0x7e233018) at
>     ShellPkg/Application/Shell/Shell.c:2732
> tianocore#10 0x000000007d4867c8 in DoShellPrompt () at
>     ShellPkg/Application/Shell/Shell.c:1349
> tianocore#11 0x000000007d48524d in UefiMain (ImageHandle=0x7e24c898,
>     SystemTable=0x7f5b6018) at ShellPkg/Application/Shell/Shell.c:631

Cc: Jaben Carsey <[email protected]>
Cc: Marvin Häuser <[email protected]>
Cc: Qiu Shumin <[email protected]>
Cc: Ruiyu Ni <[email protected]>
Fixes: bd3fc81
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <[email protected]>

Author: Laszlo Ersek

ShellPkg/Application/Shell/Shell.c

@@ -1810,7 +1810,6 @@ RunSplitCommand(
   }
   if (Split->SplitStdIn != NULL) {
     ShellInfoObject.NewEfiShellProtocol->CloseFile (Split->SplitStdIn);
-    FreePool (Split->SplitStdIn);
   }
 
   FreePool(Split);