From c0c509ca2d99c4f8af4603d7a5532b264b6083af Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Fri, 14 Aug 2026 13:41:16 +0200
Subject: [PATCH] misc: Fix out-of-bounds array write in tdelete (bug 34506)

Allocate the maximum array sizes directly, instead of resizing
the arrays as needed.  This eliminates alloca usage from the
function, and fixes the out-of-bounds accesses.  The asserts
guard against the bug coming back if the balancing of the tree
turns out not to work correctly.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
---
 misc/tsearch.c | 31 +++++++++++--------------------
 1 file changed, 11 insertions(+), 20 deletions(-)

diff --git a/misc/tsearch.c b/misc/tsearch.c
index d7dd4d9c8f..0113953e83 100644
--- a/misc/tsearch.c
+++ b/misc/tsearch.c
@@ -85,6 +85,7 @@
 #include <assert.h>
 #include <stdalign.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <search.h>
@@ -406,12 +407,13 @@ __tdelete (const void *key, void **vrootp, __compar_fn_t compar)
   int cmp;
   node *rootp = (node *) vrootp;
   node root, unchained;
-  /* Stack of nodes so we remember the parents without recursion.  It's
-     _very_ unlikely that there are paths longer than 40 nodes.  The tree
-     would need to have around 250.000 nodes.  */
-  int stacksize = 40;
+  /* Stack of nodes so we remember the parents without recursion.  The
+     stack size is a conservative approximation of the maximum height
+     of a red-black tree, based on size of the address space.
+     Actual numbers are closer to 57 (32 bit) and 117 (63 bit).  */
+  enum { stacksize = 2 * UINTPTR_WIDTH };
   int sp = 0;
-  node **nodestack = alloca (sizeof (node *) * stacksize);
+  node *nodestack[stacksize];
 
   if (rootp == NULL)
     return NULL;
@@ -424,14 +426,7 @@ __tdelete (const void *key, void **vrootp, __compar_fn_t compar)
   root = DEREFNODEPTR(rootp);
   while ((cmp = (*compar) (key, root->key)) != 0)
     {
-      if (sp == stacksize)
-	{
-	  node **newstack;
-	  stacksize += 20;
-	  newstack = alloca (sizeof (node *) * stacksize);
-	  nodestack = memcpy (newstack, nodestack, sp * sizeof (node *));
-	}
-
+      assert (sp < stacksize);
       nodestack[sp++] = rootp;
       p = DEREFNODEPTR(rootp);
       if (cmp < 0)
@@ -470,13 +465,7 @@ __tdelete (const void *key, void **vrootp, __compar_fn_t compar)
       node upn;
       for (;;)
 	{
-	  if (sp == stacksize)
-	    {
-	      node **newstack;
-	      stacksize += 20;
-	      newstack = alloca (sizeof (node *) * stacksize);
-	      nodestack = memcpy (newstack, nodestack, sp * sizeof (node *));
-	    }
+	  assert (sp < stacksize);
 	  nodestack[sp++] = parentp;
 	  parentp = up;
 	  upn = DEREFNODEPTR(up);
@@ -541,6 +530,7 @@ __tdelete (const void *key, void **vrootp, __compar_fn_t compar)
 		  SETNODEPTR(pp,q);
 		  /* Make sure pp is right if the case below tries to use
 		     it.  */
+		  assert (sp < stacksize);
 		  nodestack[sp++] = pp = LEFTPTR(q);
 		  q = RIGHT(p);
 		}
@@ -625,6 +615,7 @@ __tdelete (const void *key, void **vrootp, __compar_fn_t compar)
 		  SETLEFT(p,RIGHT(q));
 		  SETRIGHT(q,p);
 		  SETNODEPTR(pp,q);
+		  assert (sp < stacksize);
 		  nodestack[sp++] = pp = RIGHTPTR(q);
 		  q = LEFT(p);
 		}
-- 
2.55.0