GNU bug report logs - #62039
Emacs crashes while parsing a long Emacs Lisp string

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#62039: closed (Emacs crashes while parsing a long Emacs Lisp
 string)
Date: Sat, 11 Mar 2023 09:26:02 +0000

[Message part 1 (text/plain, inline)]

Your message dated Sat, 11 Mar 2023 10:25:34 +0100
with message-id <3624E3C3-1A2F-46A8-9C3B-0AB3CC7E5EC8 <at> acm.org>
and subject line Re: bug#62039: Emacs crashes while parsing a long Emacs Lisp string
has caused the debbugs.gnu.org bug report #62039,
regarding Emacs crashes while parsing a long Emacs Lisp string
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
62039: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=62039
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Contact help-debbugs <at> gnu.org with problems

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From: Bruno Haible <bruno <at> clisp.org>
To: bug-gnu-emacs <at> gnu.org
Subject: Emacs crashes while parsing a long Emacs Lisp string
Date: Tue, 07 Mar 2023 22:51:58 +0100

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When parsing a particular long Emacs Lisp string, Emacs crashes.

How to reproduce:

$ emacs -Q -batch -f batch-byte-compile foo.el
Segmentation fault

Find attached the compressed file foo.el.

Emacs version: 27.1
Platform: x86_64-linux-gnu
$ ulimit -a | grep stack
stack size                  (kbytes, -s) 8192

According to the documentation
https://www.gnu.org/software/emacs/manual/html_node/emacs/Bug-Criteria.html
any segmentation fault is a bug.

I haven't analyzed the security impact of this bug, but it is quite possible
that emacs receives a string through the network, and even though the string
is not meant to be evaluated, simply parsing it causes a denial-of-service
to the emacs user.

The cause of the bug is that in emacs/src/lread.c the function read_escape()
is recursive, and no bound on the recursion depth is enforced.

[foo.el.gz (application/gzip, attachment)]

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Bruno Haible <bruno <at> clisp.org>
Cc: 62039-done <at> debbugs.gnu.org
Subject: Re: bug#62039: Emacs crashes while parsing a long Emacs Lisp string
Date: Sat, 11 Mar 2023 10:25:34 +0100

Now fixed on master. Thanks again for the report.

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