branch release/7.1 updated: * info/scan.c (write_tag_contents): Check if added text is of zero length in order to avoid subsequently calling memcpy with a null source argument. Report with -fsanitize=undefined on amd64 from Sam James <address@hidden>.

[Gavin D. Smith]

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gavin pushed a commit to branch release/7.1
in repository texinfo.

The following commit(s) were added to refs/heads/release/7.1 by this push:
     new 12ad80f3a1 * info/scan.c (write_tag_contents): Check if added text is 
of zero length in order to avoid subsequently calling memcpy with a null source 
argument.  Report with -fsanitize=undefined on amd64 from Sam James 
<sam@gentoo.org>.
12ad80f3a1 is described below

commit 12ad80f3a1cfa78c8a7b3a45458df7e07251317d
Author: Gavin Smith <gavinsmith0123@gmail.com>
AuthorDate: Sat Nov 4 10:38:48 2023 +0000

    * info/scan.c (write_tag_contents): Check if added text is of
    zero length in order to avoid subsequently calling memcpy with
    a null source argument.  Report with -fsanitize=undefined on amd64
    from Sam James <sam@gentoo.org>.
---
 ChangeLog   | 7 +++++++
 info/scan.c | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 3d13a15517..efbb3b22d1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2023-11-04  Gavin Smith <gavinsmith0123@gmail.com>
+
+       * info/scan.c (write_tag_contents): Check if added text is of
+       zero length in order to avoid subsequently calling memcpy with
+       a null source argument.  Report with -fsanitize=undefined on amd64
+       from Sam James <sam@gentoo.org>.
+
 2023-10-25  Eli Zaretskii <eliz@gnu.org>
 
        * tp/Texinfo/XS/xspara.c (xspara__add_next): Do not pass
diff --git a/info/scan.c b/info/scan.c
index d6183ae9ae..bdf272f9bf 100644
--- a/info/scan.c
+++ b/info/scan.c
@@ -925,11 +925,11 @@ write_extra_bytes_to_output (char *input, long n)
 }
 
 /* Like write_extra_bytes_to_output, but writes bytes even when
-   preprocess_nodes=Off. */
+   preprocess_nodes=Off.  Note n could be 0 for an index tag. */
 static void
 write_tag_contents (char *input, long n)
 {
-  if (rewrite_p)
+  if (rewrite_p && n > 0)
     {
       text_buffer_add_string (&output_buf, input, n);
       output_bytes_difference -= n;