[libpng17] Simplified and future-proofed png_user_version_check().

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.7.0beta40 - November 4, 2014
+Libpng 1.7.0beta40 - November 5, 2014
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -620,9 +620,13 @@ Version 1.7.0beta38 [October 17, 2014]
 Version 1.7.0beta39 [November 1, 2014]
   Ported cosmetic changes from libpng-1.6.15beta02.
 
-Version 1.7.0beta40 [November 4, 2014]
+Version 1.7.0beta40 [November 5, 2014]
   Made a one-line revision to configure.ac to support ARM on aarch64
     (bug report by Marcin Juszkiewicz, fix by John Bowler).
+  Use png_get_libpng_ver(NULL) instead of PNG_LIBPNG_VER_STRING in
+    example.c, pngtest.c, and applications in the contrib directory.
+  Avoid out-of-bounds memory access in png_user_version_check().
+  Simplified and future-proofed png_user_version_check().
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

CHANGES

@@ -4909,9 +4909,13 @@ Version 1.7.0beta38 [October 17, 2014]
 Version 1.7.0beta39 [November 1, 2014]
   Ported cosmetic changes from libpng-1.6.15beta02.
 
-Version 1.7.0beta40 [November 4, 2014]
+Version 1.7.0beta40 [November 5, 2014]
   Made a one-line revision to configure.ac to support ARM on aarch64
     (bug report by Marcin Juszkiewicz, fix by John Bowler).
+  Use png_get_libpng_ver(NULL) instead of PNG_LIBPNG_VER_STRING in
+    example.c, pngtest.c, and applications in the contrib directory.
+  Avoid out-of-bounds memory access in png_user_version_check().
+  Simplified and future-proofed png_user_version_check().
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

png.c

@@ -165,15 +165,25 @@ png_calculate_crc(png_structrp png_ptr, png_const_bytep ptr, png_size_t length)
 int
 png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver)
 {
+     /* Libpng versions 1.0.0 and later are binary compatible if the version
+      * string matches through the second '.'; we must recompile any
+      * applications that use any older library version.
+      */
+
    if (user_png_ver != NULL)
    {
-      int i = 0;
+      int i = -1;
+      int found_dots = 0;
 
       do
       {
-         if (user_png_ver[i] != png_libpng_ver[i])
+         i++;
+         if (user_png_ver[i] != PNG_LIBPNG_VER_STRING[i])
             png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;
-      } while (png_libpng_ver[i++]);
+         if (user_png_ver[i] == '.')
+            found_dots++;
+      } while (found_dots < 2 && user_png_ver[i] != 0 &&
+            PNG_LIBPNG_VER_STRING[i] != 0);
    }
 
    else
@@ -181,17 +191,6 @@ png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver)
 
    if ((png_ptr->flags & PNG_FLAG_LIBRARY_MISMATCH) != 0)
    {
-     /* Libpng 0.90 and later are binary incompatible with libpng 0.89, so
-      * we must recompile any applications that use any older library version.
-      * For versions after libpng 1.0, we will be compatible, so we need
-      * only check the first and third digits (note that when we reach version
-      * 1.10 we will need to check the fourth symbol, namely user_png_ver[3]).
-      */
-      if (user_png_ver == NULL || user_png_ver[0] != png_libpng_ver[0] ||
-          (user_png_ver[0] == '1' && (user_png_ver[2] != png_libpng_ver[2] ||
-          user_png_ver[3] != png_libpng_ver[3])) ||
-          (user_png_ver[0] == '0' && user_png_ver[2] < '9'))
-      {
 #ifdef PNG_WARNINGS_SUPPORTED
       size_t pos = 0;
       char m[128];
@@ -200,7 +199,7 @@ png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver)
           "Application built with libpng-");
       pos = png_safecat(m, (sizeof m), pos, user_png_ver);
       pos = png_safecat(m, (sizeof m), pos, " but running with ");
-         pos = png_safecat(m, (sizeof m), pos, png_libpng_ver);
+      pos = png_safecat(m, (sizeof m), pos, PNG_LIBPNG_VER_STRING);
       PNG_UNUSED(pos)
 
       png_warning(png_ptr, m);
@@ -212,12 +211,10 @@ png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver)
 
       return 0;
    }
-   }
 
    /* Success return. */
    return 1;
 }
-
 /* Generic function to create a png_struct for either read or write - this
  * contains the common initialization.
  */
@@ -694,13 +691,13 @@ png_get_copyright(png_const_structrp png_ptr)
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
-     "libpng version 1.7.0beta40 - November 1, 2014" PNG_STRING_NEWLINE \
+     "libpng version 1.7.0beta40 - November 5, 2014" PNG_STRING_NEWLINE \
      "Copyright (c) 1998-2014 Glenn Randers-Pehrson" PNG_STRING_NEWLINE \
      "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
      "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
      PNG_STRING_NEWLINE;
 #  else
-      return "libpng version 1.7.0beta40 - November 1, 2014\
+      return "libpng version 1.7.0beta40 - November 5, 2014\
       Copyright (c) 1998-2014 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
       Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";