--- /dev/null
+From 2a3129365d3bc0d4a41f107ef175920d1505d1f7 Mon Sep 17 00:00:00 2001
+From: Chris Liddell <chris.liddell@artifex.com>
+Date: Tue, 1 Jun 2021 19:57:16 +0100
+Subject: [PATCH] Bug 703902: Fix op stack management in
+ sampled_data_continue()
+
+Replace pop() (which does no checking, and doesn't handle stack extension
+blocks) with ref_stack_pop() which does do all that.
+
+We still use pop() in one case (it's faster), but we have to later use
+ref_stack_pop() before calling sampled_data_sample() which also accesses the
+op stack.
+
+Fixes:
+https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=34675
+
+Upstream-Status: Backported [https://git.ghostscript.com/?p=ghostpdl.git;a=commit;h=2a3129365d3bc0d4a41f107ef175920d1505d1f7]
+CVE: CVE-2021-45949
+Signed-off-by: Lee Chee Yang <chee.yang.lee@intel.com>
+---
+ psi/zfsample.c | 16 ++++++++++------
+ 1 file changed, 10 insertions(+), 6 deletions(-)
+
+diff --git a/psi/zfsample.c b/psi/zfsample.c
+index 0e8e4bc8d..00cd0cfdd 100644
+--- a/psi/zfsample.c
++++ b/psi/zfsample.c
+@@ -533,15 +533,19 @@ sampled_data_continue(i_ctx_t *i_ctx_p)
+ for (j = 0; j < bps; j++)
+ data_ptr[bps * i + j] = (byte)(cv >> ((bps - 1 - j) * 8)); /* MSB first */
+ }
+- pop(num_out); /* Move op to base of result values */
+
+- /* Check if we are done collecting data. */
++ pop(num_out); /* Move op to base of result values */
+
++ /* From here on, we have to use ref_stack_pop() rather than pop()
++ so that it handles stack extension blocks properly, before calling
++ sampled_data_sample() which also uses the op stack.
++ */
++ /* Check if we are done collecting data. */
+ if (increment_cube_indexes(params, penum->indexes)) {
+ if (stack_depth_adjust == 0)
+- pop(O_STACK_PAD); /* Remove spare stack space */
++ ref_stack_pop(&o_stack, O_STACK_PAD); /* Remove spare stack space */
+ else
+- pop(stack_depth_adjust - num_out);
++ ref_stack_pop(&o_stack, stack_depth_adjust - num_out);
+ /* Execute the closing procedure, if given */
+ code = 0;
+ if (esp_finish_proc != 0)
+@@ -554,11 +558,11 @@ sampled_data_continue(i_ctx_t *i_ctx_p)
+ if ((O_STACK_PAD - stack_depth_adjust) < 0) {
+ stack_depth_adjust = -(O_STACK_PAD - stack_depth_adjust);
+ check_op(stack_depth_adjust);
+- pop(stack_depth_adjust);
++ ref_stack_pop(&o_stack, stack_depth_adjust);
+ }
+ else {
+ check_ostack(O_STACK_PAD - stack_depth_adjust);
+- push(O_STACK_PAD - stack_depth_adjust);
++ ref_stack_push(&o_stack, O_STACK_PAD - stack_depth_adjust);
+ for (i=0;i<O_STACK_PAD - stack_depth_adjust;i++)
+ make_null(op - i);
+ }
+--
+2.25.1
+
