bug#53333: Fix for crash in ebrowse

[Jan Stranik via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Hello --

attached is a patch to ebrowse. Noticed a one-off write error in case of
identifiers that are too long and need escaping. The patch prevents the
write to memory outside of allocated range which on my platform caused
segfault.

Best,



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Dont crash on C source code (one off error)

The fix avoids one off error in case the last character in the buffer
needs to be escaped but there is not enough space in buffer to perform
the escape.

The change just simiply ignores the character in such case.

Author: Jan Stranik <jan@stranik.org>


*** /var/home/janstranik/src/emacs-27.2/lib-src/ebrowse.c~	2021-01-28 11:52:16.000000000 -0600
--- /var/home/janstranik/src/emacs-27.2/lib-src/ebrowse.c	2021-09-24 09:31:49.136287028 -0500
***************
*** 1924,1931 ****
      {
        *--s = *--t;
  
!       if (*s == '"' || *s == '\\')
!         *--s = '\\';
      }
  
    *(matching_regexp_end_buf - 1) = '\0';
--- 1924,1937 ----
      {
        *--s = *--t;
  
!       if (*s == '"' || *s == '\\') {
!           if (s > matching_regexp_buffer)
!               *--s = '\\';
!           else {
!               s++;
!               break;
!           }
!       }
      }
  
    *(matching_regexp_end_buf - 1) = '\0';

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-- 

Jan Stranik