[freetype2] master 8d7b919 2/2: [lzw] Avoid buffer overrun.

[Werner LEMBERG]

branch: master
commit 8d7b9198e3830bb1ae37ac3b3f44c60582c86f81
Author: Werner Lemberg <address@hidden>
Commit: Werner Lemberg <address@hidden>

    [lzw] Avoid buffer overrun.
    
    Reported as
    
      https://bugzilla.mozilla.org/show_bug.cgi?id=1273283
    
    * src/lzw/ftzopen.c (ft_lzwstate_refill): Ensure `buf_size' doesn't
    underflow.
---
 ChangeLog         |   11 +++++++++++
 src/lzw/ftzopen.c |    7 ++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 3cf0002..da002ab 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
 2016-08-16  Werner Lemberg  <address@hidden>
 
+       [lzw] Avoid buffer overrun.
+
+       Reported as
+
+         https://bugzilla.mozilla.org/show_bug.cgi?id=1273283
+
+       * src/lzw/ftzopen.c (ft_lzwstate_refill): Ensure `buf_size' doesn't
+       underflow.
+
+2016-08-16  Werner Lemberg  <address@hidden>
+
        [truetype] Fix compiler warning.
 
        * src/truetype/ttgload.c (load_truetype_glyph): Add cast.
diff --git a/src/lzw/ftzopen.c b/src/lzw/ftzopen.c
index e17b3c5..32839cc 100644
--- a/src/lzw/ftzopen.c
+++ b/src/lzw/ftzopen.c
@@ -42,7 +42,12 @@
     state->buf_total += count;
     state->in_eof     = FT_BOOL( count < state->num_bits );
     state->buf_offset = 0;
-    state->buf_size   = ( state->buf_size << 3 ) - ( state->num_bits - 1 );
+
+    state->buf_size <<= 3;
+    if ( state->buf_size > state->num_bits )
+      state->buf_size -= state->num_bits - 1;
+    else
+      return -1; /* not enough data */
 
     if ( count == 0 )  /* end of file */
       return -1;