bug#52369: 28.0.90; Assertion failure when running Flycheck unit test suite

[Philipp Stephani <p.stephani2@gmail.com>]

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Am Mi., 8. Dez. 2021 um 09:43 Uhr schrieb Philipp Stephani
<p.stephani2@gmail.com>:
>
>
> With the emacs-28 branch (haven't checked other branches so far), an
> assertion failure consistently triggers when running the Flycheck unit
> test suite.  Unfortunately, I haven't been able to narrow down the
> problem any further so far.  To reproduce, clone the Flycheck repository
> from https://github.com/flycheck/flycheck (at commit
> 784f184cdd9f9cb4e3dbb997c09d93e954142842 in my case, though this
> probably doesn't matter much), and run the unit tests like
>
> export EMACS=...
> make init
> make unit
>
> With an Emacs built with --enable-checking, I then get the following
> assertion failure:
>
> [...]
>    passed  302/361  flycheck-set-checker-executable/non-existing-file (0.000481 sec)
>    passed  303/361  flycheck-set-checker-executable/real-executable (0.002321 sec)
>    passed  304/361  flycheck-standard-error-navigation/default-to-t (0.000198 sec)
>
> process.c:6521: Emacs fatal error: assertion failed: 0 <= outfd && outfd < FD_SETSIZE
> make: *** [Makefile:128: unit] Aborted (core dumped)
>

Given that this is a serious bug (undefined behavior), I'd install the
attached patch on the release branch.

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From d39bdfbb64c953bd9389f762443d15ecb4fb0cbb Mon Sep 17 00:00:00 2001
From: Philipp Stephani <phst@google.com>
Date: Sat, 11 Dec 2021 13:51:34 +0100
Subject: [PATCH] Avoid undefined behavior in 'send-process-region'
 (Bug#52369).

* src/process.c (send_process): Signal an error if the file descriptor
has already been closed.
---
 src/process.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/process.c b/src/process.c
index 75ba191fa1..1d307d5242 100644
--- a/src/process.c
+++ b/src/process.c
@@ -6520,6 +6520,9 @@ send_process (Lisp_Object proc, const char *buf, ptrdiff_t len,
 	  /* Send this batch, using one or more write calls.  */
 	  ptrdiff_t written = 0;
 	  int outfd = p->outfd;
+          if (outfd < 0)
+            error ("Output file descriptor of %s is closed",
+                   SDATA (p->name));
 	  eassert (0 <= outfd && outfd < FD_SETSIZE);
 #ifdef DATAGRAM_SOCKETS
 	  if (DATAGRAM_CHAN_P (outfd))
-- 
2.30.1 (Apple Git-130)