[Mesa-dev] [PATCH] i965: fix problem with constant out of bounds access

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

This is my attempt at fixing this as the CVE is making RH security team
care enough to make me look at this. (please upstream, security fixes are
more important than whatever else you are doing, if for no other reason than
it saves me having to fix stuff I've no real clue about).

Since Frank's original fix was denied, here is my attempt to just
alias all constants that are out of bounds < 0 or > nr_params to constant 0,
hopefully this provides the undefined behaviour idr requires..

CVE-2013-1872

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 src/mesa/drivers/dri/i965/brw_fs.cpp         | 12 +++++++++++-
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |  1 +
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index baaa25c..62dbe71 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -1504,7 +1504,13 @@ fs_visitor::remove_dead_constants()
 	    if (inst->src[i].file != UNIFORM)
 	       continue;
 
-	    assert(constant_nr < (int)c->prog_data.nr_params);
+            /* if we get a negative constant nr or one greater than we can
+             * handle, this can cause an overflow, we can't just refuse to
+             * build, so just go undefined and alias everyone to constant 0.
+             */
+	    if (constant_nr < 0 || constant_nr >= (int)c->prog_data.nr_params) {
+               constant_nr = 0;
+	    }
 
 	    /* For now, set this to non-negative.  We'll give it the
 	     * actual new number in a moment, in order to keep the
@@ -1552,6 +1558,10 @@ fs_visitor::remove_dead_constants()
 	 if (inst->src[i].file != UNIFORM)
 	    continue;
 
+         /* as above alias to 0 */
+         if (constant_nr < 0 || constant_nr >= (int)c->prog_data.nr_params) {
+            constant_nr = 0;
+         }
 	 assert(this->params_remap[constant_nr] != -1);
 	 inst->src[i].reg = this->params_remap[constant_nr];
 	 inst->src[i].reg_offset = 0;
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 36d9cf0..07c8088 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -2467,6 +2467,7 @@ fs_visitor::fs_visitor(struct brw_context *brw,
    this->force_sechalf_stack = 0;
 
    memset(&this->param_size, 0, sizeof(this->param_size));
+   this->params_remap = NULL;
 }
 
 fs_visitor::~fs_visitor()
-- 
1.8.1.4