From: Eli Zaretskii <eliz@gnu.org>
Date: Sat, 9 Jul 2022 10:16:12 +0000 (+0300)
Subject: Fix segfault in composite.c
X-Git-Tag: emacs-29.0.90~1447^2~821^2~15
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=a740608453525c7f7645df0740ee8267b43a779b;p=emacs.git

Fix segfault in composite.c

* src/composite.c (find_automatic_composition): Don't use
narrowed_begv if it's zero.  This avoids segfault in
BACKWARD_CHAR, since zero is not a valid buffer position.
---

diff --git a/src/composite.c b/src/composite.c
index d8998b5a1f3..4f7b4b0a2c7 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -1590,7 +1590,7 @@ find_automatic_composition (ptrdiff_t pos, ptrdiff_t limit, ptrdiff_t backlim,
       /* In buffers with very long lines, this function becomes very
 	 slow.  Pretend that the buffer is narrowed to make it fast.  */
       narrowed_begv = get_narrowed_begv (w);
-      if (pos > narrowed_begv)
+      if (narrowed_begv && pos > narrowed_begv)
 	head = narrowed_begv;
       cur.pos_byte = CHAR_TO_BYTE (cur.pos);
       cur.p = BYTE_POS_ADDR (cur.pos_byte);