Re: [ros-dev] [ros-diffs] [tfaber] 64762: [NPFS] - Don't call RtlEqualUnicodeString (paged code) while holding a spin lock. Powered by Driver Verifier.

[Thomas Faber]

RtlEqualUnicodeString is in a pagable code section in ntoskrnl,
RtlCompareMemory is not. Holding a spinlock means we're at
DISPATCH_LEVEL and can't access pagable code/data.


On 2014-10-16 19:32, Hermès BÉLUSCA - MAÏTO wrote:
>   What is the *root* reason for this problem (ok I’ve
> seen in the comment,
>  “paged code” and “holding spin lock”, but it doesn’t answer my question)?
>  Because I’ve looked at our code of RtlEqualUnicodeString and I see that it
>  just calls RtlCompareUnicodeString that in turns just loops over the two
>  memory buffers, checks their contents (and in case we check for char case,
>  calls RtlUpcaseUnicodeChar). And RtlCompareMemory does that, too? What I’m
>  missing?
>  
>  Hermès.
>  
>  
>  -------------------------------------------------------------------------
>  Author: tfaber
>  Date: Thu Oct 16 16:40:13 2014
>  New Revision: 64762
>  
>  URL: http://svn.reactos.org/svn/reactos?rev=64762&view=rev
>  Log:
>  [NPFS]
>  - Don't call RtlEqualUnicodeString (paged code) while holding a spin lock.
>  Powered by Driver Verifier.
>  
>  Modified:
>      trunk/reactos/drivers/filesystems/npfs/waitsup.c
>  
>  Modified: trunk/reactos/drivers/filesystems/npfs/waitsup.c
>  URL:
>  http://svn.reactos.org/svn/reactos/trunk/reactos/drivers/filesystems/npfs/wa
>  itsup.c?rev=64762&r1=64761&r2=64762&view=diff
>  ============================================================================
>  ==
>  --- trunk/reactos/drivers/filesystems/npfs/waitsup.c	[iso-8859-1]
>  (original)
>  +++ trunk/reactos/drivers/filesystems/npfs/waitsup.c	[iso-8859-1] Thu Oct
>  16 16:40:13 2014
>  @@ -97,6 +97,22 @@
>   {
>       InitializeListHead(&WaitQueue->WaitList);
>       KeInitializeSpinLock(&WaitQueue->WaitLock);
>  +}
>  +
>  +static
>  +BOOLEAN
>  +NpEqualUnicodeString(IN PCUNICODE_STRING String1,
>  +                     IN PCUNICODE_STRING String2)
>  +{
>  +    SIZE_T EqualLength;
>  +
>  +    if (String1->Length != String2->Length)
>  +        return FALSE;
>  +
>  +    EqualLength = RtlCompareMemory(String1->Buffer,
>  +                                   String2->Buffer,
>  +                                   String1->Length);
>  +    return EqualLength == String1->Length;
>   }
>   
>   NTSTATUS
>  @@ -156,7 +172,8 @@
>               PipeName.MaximumLength = PipeName.Length;
>           }
>   
>  -        if (RtlEqualUnicodeString(&WaitName, &PipeName, FALSE))
>  +        /* Can't use RtlEqualUnicodeString with a spinlock held */
>  +        if (NpEqualUnicodeString(&WaitName, &PipeName))
>           {
>               /* Found a matching wait. Cancel it */
>               RemoveEntryList(&WaitIrp->Tail.Overlay.ListEntry);
>