svn commit: r367120 - head/sys/kern

[Konstantin Belousov]

Author: kib
Date: Wed Oct 28 22:12:47 2020
New Revision: 367120
URL: https://svnweb.freebsd.org/changeset/base/367120

Log:
  Check for process group change in tty_wait_background().
  
  The calling process's process group can change between PROC_UNLOCK(p)
  and PGRP_LOCK(pg) in tty_wait_background(), e.g. by a setpgid() call
  from another process. If that happens, the signal is not sent to the
  calling process, even if the prior checks determine that one should be
  sent.  Re-check that the process group hasn't changed after acquiring
  the pgrp lock, and if it has, redo the checks.
  
  PR:	250701
  Submitted by:	Jakub Piecuch <j.piecuch96 at gmail.com>
  MFC after:	2 weeks

Modified:
  head/sys/kern/tty.c

Modified: head/sys/kern/tty.c
==============================================================================
--- head/sys/kern/tty.c	Wed Oct 28 21:18:04 2020	(r367119)
+++ head/sys/kern/tty.c	Wed Oct 28 22:12:47 2020	(r367120)
@@ -474,6 +474,19 @@ tty_wait_background(struct tty *tp, struct thread *td,
 			sig = 0;
 		}
 		PGRP_LOCK(pg);
+
+		/*
+		 * pg may no longer be our process group.
+		 * Re-check after locking process group.
+		 */
+		PROC_LOCK(p);
+		if (p->p_pgrp != pg) {
+			PROC_UNLOCK(p);
+			PGRP_UNLOCK(pg);
+			continue;
+		}
+
+		PROC_UNLOCK(p);
 		pgsignal(pg, ksi.ksi_signo, 1, &ksi);
 		PGRP_UNLOCK(pg);