[reactos] 01/02: [NTOSKRNL] Fix our-of-bounds access and memory leak (CID-1401178, 1401177) in FsRtlIsDbcsInExpression

[Timo Kreuzer]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=561f18afeae0040c79918…

commit 561f18afeae0040c7991810c6e9ab3cb58fddf84
Author: Timo Kreuzer <timo.kreuzer(a)reactos.org>
AuthorDate: Wed Oct 11 14:20:57 2017 +0200

    [NTOSKRNL] Fix our-of-bounds access and memory leak (CID-1401178, 1401177) in
FsRtlIsDbcsInExpression
---
 ntoskrnl/fsrtl/dbcsname.c | 52 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 37 insertions(+), 15 deletions(-)

diff --git a/ntoskrnl/fsrtl/dbcsname.c b/ntoskrnl/fsrtl/dbcsname.c
index ccaaa9b37c..306c5474b2 100644
--- a/ntoskrnl/fsrtl/dbcsname.c
+++ b/ntoskrnl/fsrtl/dbcsname.c
@@ -163,6 +163,8 @@ FsRtlIsDbcsInExpression(IN PANSI_STRING Expression,
     USHORT Offset, Position, BackTrackingPosition, OldBackTrackingPosition;
     USHORT BackTrackingBuffer[16], OldBackTrackingBuffer[16] = {0};
     PUSHORT BackTrackingSwap, BackTracking = BackTrackingBuffer, OldBackTracking =
OldBackTrackingBuffer;
+    ULONG BackTrackingBufferSize = RTL_NUMBER_OF(BackTrackingBuffer);
+    PVOID AllocatedBuffer = NULL;
     USHORT ExpressionPosition, NamePosition = 0, MatchingChars = 1;
     USHORT NameChar = 0, ExpressionChar;
     BOOLEAN EndOfName = FALSE;
@@ -281,22 +283,40 @@ FsRtlIsDbcsInExpression(IN PANSI_STRING Expression,
                 }
 
                 /* If buffer too small */
-                if (BackTrackingPosition > RTL_NUMBER_OF(BackTrackingBuffer) - 1)
+                if (BackTrackingPosition > BackTrackingBufferSize - 2)
                 {
-                    /* Allocate memory for BackTracking */
-                    BackTracking = ExAllocatePoolWithTag(PagedPool |
POOL_RAISE_IF_ALLOCATION_FAILURE,
-                                                         (Expression->Length + 1) *
sizeof(USHORT) * 2,
-                                                         'nrSF');
-                    /* Copy old buffer content */
+                    /* We should only ever get here once! */
+                    ASSERT(AllocatedBuffer == NULL);
+                    ASSERT((BackTracking == BackTrackingBuffer) || (BackTracking ==
OldBackTrackingBuffer));
+                    ASSERT((OldBackTracking == BackTrackingBuffer) || (OldBackTracking ==
OldBackTrackingBuffer));
+
+                    /* Calculate buffer size */
+                    BackTrackingBufferSize = (Expression->Length + 1) * 2;
+
+                    /* Allocate memory for both back-tracking buffers */
+                    AllocatedBuffer = ExAllocatePoolWithTag(PagedPool |
POOL_RAISE_IF_ALLOCATION_FAILURE,
+                                                            2 * BackTrackingBufferSize *
sizeof(USHORT),
+                                                            'nrSF');
+                    if (AllocatedBuffer == NULL)
+                    {
+                        DPRINT1("Failed to allocate BackTracking buffer.
BackTrackingBufferSize = =x%lx\n",
+                                BackTrackingBufferSize);
+                        Result = FALSE;
+                        goto Exit;
+                    }
+
+                    /* Backtracking is at the start of the buffer */
+                    BackTracking = AllocatedBuffer;
+
+                    /* Copy BackTrackingBuffer content */
                     RtlCopyMemory(BackTracking,
                                   BackTrackingBuffer,
                                   RTL_NUMBER_OF(BackTrackingBuffer) * sizeof(USHORT));
 
-                    /* Allocate memory for OldBackTracking */
-                    OldBackTracking = ExAllocatePoolWithTag(PagedPool |
POOL_RAISE_IF_ALLOCATION_FAILURE,
-                                                            (Expression->Length + 1) *
sizeof(USHORT) * 2,
-                                                            'nrSF');
-                    /* Copy old buffer content */
+                    /* OldBackTracking is after BackTracking */
+                    OldBackTracking = &BackTracking[BackTrackingBufferSize];
+
+                    /* Copy OldBackTrackingBuffer content */
                     RtlCopyMemory(OldBackTracking,
                                   OldBackTrackingBuffer,
                                   RTL_NUMBER_OF(OldBackTrackingBuffer) *
sizeof(USHORT));
@@ -404,11 +424,13 @@ FsRtlIsDbcsInExpression(IN PANSI_STRING Expression,
     /* Store result value */
     Result = (OldBackTracking[MatchingChars - 1] == Expression->Length * 2);
 
+Exit:
+
     /* Frees the memory if necessary */
-    if (BackTracking != BackTrackingBuffer && BackTracking !=
OldBackTrackingBuffer)
-        ExFreePoolWithTag(BackTracking, 'nrSF');
-    if (OldBackTracking != BackTrackingBuffer && OldBackTracking !=
OldBackTrackingBuffer)
-        ExFreePoolWithTag(OldBackTracking, 'nrSF');
+    if (AllocatedBuffer != NULL)
+    {
+        ExFreePoolWithTag(AllocatedBuffer, 'nrSF');
+    }
 
     return Result;
 }