From c5274dd12224421f2430b30c53b881b9403d649e Mon Sep 17 00:00:00 2001
From: Bram Moolenaar <Bram@vim.org>
Date: Sat, 2 Jul 2022 15:10:00 +0100
Subject: [PATCH] patch 9.0.0026: accessing freed memory with diff put

Problem:    Accessing freed memory with diff put.
Solution:   Bail out when diff pointer is no longer valid.
---
 src/diff.c    | 24 ++++++++++++++++++++++--
 1 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/diff.c b/src/diff.c
index 91e5ae2..e4bafe2 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -2643,6 +2643,20 @@ nv_diffgetput(int put, long count)
 }
 
 /*
+ * Return TRUE if "diff" appears in the list of diff blocks of the current tab.
+ */
+    static int
+valid_diff(diff_T *diff)
+{
+    diff_T	*dp;
+
+    for (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)
+	if (dp == diff)
+	    return TRUE;
+    return FALSE;
+}
+
+/*
  * ":diffget"
  * ":diffput"
  */
@@ -2899,9 +2913,9 @@ ex_diffgetput(exarg_T *eap)
 		}
 	    }
 
-	    // Adjust marks.  This will change the following entries!
 	    if (added != 0)
 	    {
+		// Adjust marks.  This will change the following entries!
 		mark_adjust(lnum, lnum + count - 1, (long)MAXLNUM, (long)added);
 		if (curwin->w_cursor.lnum >= lnum)
 		{
@@ -2923,7 +2937,13 @@ ex_diffgetput(exarg_T *eap)
 #endif
 		vim_free(dfree);
 	    }
-	    else
+
+	    // mark_adjust() may have made "dp" invalid.  We don't know where
+	    // to continue then, bail out.
+	    if (added != 0 && !valid_diff(dp))
+		break;
+
+	    if (dfree == NULL)
 		// mark_adjust() may have changed the count in a wrong way
 		dp->df_count[idx_to] = new_count;
 
-- 
1.8.3.1