[PATCH] xmllite: Avoid out of bounds access in readerinput_get_utf8_convlen().

[Paul Gofman]

And consequently in readerinput_shrinkraw().

Signed-off-by: Paul Gofman 
---
    Spotted as a crash reproducible under certain conditions during Forza Horizon 4 start.
    The out of bounds access in readerinput_get_utf8_convlen() is reproducible with the
    existing tests, that just doesn't usually result in the crash as
    'if (!(buffer->data[len-1] & 0x80)) return len;' ends up returning 0 for zero length
    most of the time.

dlls/xmllite/reader.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/dlls/xmllite/reader.c b/dlls/xmllite/reader.c
index 13d841eb94d..aa193128e4b 100644
--- a/dlls/xmllite/reader.c
+++ b/dlls/xmllite/reader.c
@@ -929,6 +929,8 @@ static int readerinput_get_utf8_convlen(xmlreaderinput *readerinput)
     encoded_buffer *buffer = &readerinput->buffer->encoded;
     int len = buffer->written;

+    assert(len);
+
     /* complete single byte char */
     if (!(buffer->data[len-1] & 0x80)) return len;

@@ -966,6 +968,7 @@ static void readerinput_shrinkraw(xmlreaderinput *readerinput, int len)
     if (len == -1)
         len = readerinput_get_convlen(readerinput);

+    assert(len >= 0);
     memmove(buffer->data, buffer->data + buffer->cur + (buffer->written - len), len);
     /* everything below cur is lost too */
     buffer->written -= len + buffer->cur;
@@ -1069,6 +1072,9 @@ static HRESULT reader_more(xmlreader *reader)

/* get some raw data from stream first */
     hr = readerinput_growraw(readerinput);
+    if (!src->written)
+        return hr ? hr : MX_E_INPUTEND;
+
     len = readerinput_get_convlen(readerinput);
     prev_len = dest->written / sizeof(WCHAR);

[Nikolay Sivov]

On 4/14/21 3:48 PM, Paul Gofman wrote:
> @@ -1069,6 +1072,9 @@ static HRESULT reader_more(xmlreader *reader)
>  /* get some raw data from stream first */
>  hr = readerinput_growraw(readerinput);
> - if (!src->written)
> -
>    return hr ? hr : MX_E_INPUTEND;
> - len = readerinput_get_convlen(readerinput);
>    prev_len = dest->written / sizeof(WCHAR);

I think it's safe to move this to growraw() directly, checking for
resulting buffer->written there.