From: Bartosz Brachaczek <b.brachaczek@gmail.com>
Date: Mon, 1 Apr 2019 00:09:23 +0000 (+0200)
Subject: [NTOSKRNL] Do not try to access OldBackTracking[-1]
X-Git-Tag: 0.4.13-dev~96
X-Git-Url: https://git.reactos.org/?p=reactos.git;a=commitdiff_plain;h=d256ff60068cafca0d3dc78f518b6617b786efe0

[NTOSKRNL] Do not try to access OldBackTracking[-1]

It can be triggered by the existing "F<", "FILE.TXT" case in the tests.

CORE-15902
---

diff --git a/ntoskrnl/fsrtl/dbcsname.c b/ntoskrnl/fsrtl/dbcsname.c
index 3b1afd801ec..362549e30b7 100644
--- a/ntoskrnl/fsrtl/dbcsname.c
+++ b/ntoskrnl/fsrtl/dbcsname.c
@@ -248,7 +248,7 @@ FsRtlIsDbcsInExpression(IN PANSI_STRING Expression,
         if (NamePosition >= Name->Length)
         {
             EndOfName = TRUE;
-            if (OldBackTracking[MatchingChars - 1] == Expression->Length * 2)
+            if (MatchingChars && OldBackTracking[MatchingChars - 1] == Expression->Length * 2)
                 break;
         }
         else
@@ -422,7 +422,7 @@ FsRtlIsDbcsInExpression(IN PANSI_STRING Expression,
     }
 
     /* Store result value */
-    Result = (OldBackTracking[MatchingChars - 1] == Expression->Length * 2);
+    Result = MatchingChars && (OldBackTracking[MatchingChars - 1] == Expression->Length * 2);
 
 Exit: