mesa: Fix segfault on reading from a missing color read buffer.

The diff looks funny, but it's moving the integer vs non-integer check
below the _mesa_source_buffer_exists() check that ensures
_ColorReadBuffer is non-null, so we get a GL_INVALID_OPERATION instead
of a segfault.  This looks like it had regressed in the
_mesa_error_check_format_and_type() changes, which removed the first of
the two duplicated checks for the source buffer.  Fixes segfault in the
new piglit ARB_framebuffer_object/negative-readpixels-no-rb.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45877
NOTE: This is a candidate for the stable branches.
Reviewed-by: Brian Paul <brianp@vmware.com>
(cherry picked from commit 5c99697f74c68f7e170564d791b95d986a18774a)

diff --git a/src/mesa/main/readpix.c b/src/mesa/main/readpix.c
index 7dc7581..41f5a07 100644 (file)
--- a/src/mesa/main/readpix.c
+++ b/src/mesa/main/readpix.c
@@ -749,6 +749,17 @@ _mesa_ReadnPixelsARB( GLint x, GLint y, GLsizei width, GLsizei height,
       return;
    }
 
+   if (_mesa_is_user_fbo(ctx->ReadBuffer) &&
+       ctx->ReadBuffer->Visual.samples > 0) {
+      _mesa_error(ctx, GL_INVALID_OPERATION, "glReadPixels(multisample FBO)");
+      return;
+   }
+
+   if (!_mesa_source_buffer_exists(ctx, format)) {
+      _mesa_error(ctx, GL_INVALID_OPERATION, "glReadPixels(no readbuffer)");
+      return;
+   }
+
    /* Check that the destination format and source buffer are both
     * integer-valued or both non-integer-valued.
     */
@@ -763,17 +774,6 @@ _mesa_ReadnPixelsARB( GLint x, GLint y, GLsizei width, GLsizei height,
       }
    }
 
-   if (_mesa_is_user_fbo(ctx->ReadBuffer) &&
-       ctx->ReadBuffer->Visual.samples > 0) {
-      _mesa_error(ctx, GL_INVALID_OPERATION, "glReadPixels(multisample FBO)");
-      return;
-   }
-
-   if (!_mesa_source_buffer_exists(ctx, format)) {
-      _mesa_error(ctx, GL_INVALID_OPERATION, "glReadPixels(no readbuffer)");
-      return;
-   }
-
    if (width == 0 || height == 0)
       return; /* nothing to do */