Date: Tue, 21 Apr 2026 15:43:13 +0000 From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: f46210a7ab32 - stable/14 - tty: Avoid leaving dangling pointers in tty_drop_ctty() Message-ID: <69e79b11.360c4.1e14808d@gitrepo.freebsd.org>
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The branch stable/14 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=f46210a7ab3227e71cd1fee16d2ede88b648a2df commit f46210a7ab3227e71cd1fee16d2ede88b648a2df Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2026-03-23 15:22:48 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2026-04-21 15:43:09 +0000 tty: Avoid leaving dangling pointers in tty_drop_ctty() The TIOCNOTTY handler detaches the calling process from its controlling terminal. It clears the link from the session to the tty, but not the pointers from the tty to the session and process group. This means that sess_release() doesn't call tty_rel_sess(), and that pgdelete() doesn't call tty_rel_pgrp(), so the pointers are left dangling. Fix this by clearing pointers in tty_drop_ctty(). Add a standalone regression test. Approved by: so Security: FreeBSD-SA-26:10.tty Security: CVE-2026-5398 Reported by: Nicholas Carlini <npc@anthropic.com> Reviewed by: kib, kevans Fixes: 1b50b999f9b5 ("tty: implement TIOCNOTTY") Differential Revision: https://reviews.freebsd.org/D56046 --- sys/kern/tty.c | 4 +++ tests/sys/kern/tty/Makefile | 1 + tests/sys/kern/tty/tiocnotty.c | 82 ++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 87 insertions(+) diff --git a/sys/kern/tty.c b/sys/kern/tty.c index 47f9f25cec37..508fa10fdd62 100644 --- a/sys/kern/tty.c +++ b/sys/kern/tty.c @@ -1262,6 +1262,10 @@ tty_drop_ctty(struct tty *tp, struct proc *p) session->s_ttydp = NULL; SESS_UNLOCK(session); + if (tp->t_session == session) { + tp->t_session = NULL; + tp->t_pgrp = NULL; + } tp->t_sessioncnt--; p->p_flag &= ~P_CONTROLT; PROC_UNLOCK(p); diff --git a/tests/sys/kern/tty/Makefile b/tests/sys/kern/tty/Makefile index 8628ab79875f..d134b3337a21 100644 --- a/tests/sys/kern/tty/Makefile +++ b/tests/sys/kern/tty/Makefile @@ -5,6 +5,7 @@ PLAIN_TESTS_PORCH+= test_canon PLAIN_TESTS_PORCH+= test_canon_fullbuf PLAIN_TESTS_PORCH+= test_ncanon PLAIN_TESTS_PORCH+= test_recanon +PLAIN_TESTS_C+= tiocnotty ATF_TESTS_C+= test_sti PROGS+= fionread diff --git a/tests/sys/kern/tty/tiocnotty.c b/tests/sys/kern/tty/tiocnotty.c new file mode 100644 index 000000000000..2581f976b2ef --- /dev/null +++ b/tests/sys/kern/tty/tiocnotty.c @@ -0,0 +1,82 @@ +/* + * Copyright (c) 2026 Mark Johnston <markj@FreeBSD.org> + * + * SPDX-License-Identifier: BSD-2-Clause + */ + +/* + * A regression test that exercises a bug where TIOCNOTTY would leave some + * dangling pointers behind in the controlling terminal structure. + */ + +#include <sys/ioctl.h> +#include <sys/wait.h> + +#include <err.h> +#include <fcntl.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +int +main(void) +{ + int master, slave, status; + pid_t child; + + master = posix_openpt(O_RDWR | O_NOCTTY); + if (master < 0) + err(1, "posix_openpt"); + if (grantpt(master) < 0) + err(1, "grantpt"); + if (unlockpt(master) < 0) + err(1, "unlockpt"); + + child = fork(); + if (child < 0) + err(1, "fork"); + if (child == 0) { + if (setsid() < 0) + err(1, "setsid"); + slave = open(ptsname(master), O_RDWR | O_NOCTTY); + if (slave < 0) + err(2, "open"); + if (ioctl(slave, TIOCSCTTY, 0) < 0) + err(3, "ioctl(TIOCSCTTY)"); + /* Detach ourselves from the controlling terminal. */ + if (ioctl(slave, TIOCNOTTY, 0) < 0) + err(4, "ioctl(TIOCNOTTY)"); + _exit(0); + } + + if (waitpid(child, &status, 0) < 0) + err(1, "waitpid"); + if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) + errx(1, "child exited with status %d", WEXITSTATUS(status)); + + child = fork(); + if (child < 0) + err(1, "fork"); + if (child == 0) { + struct winsize winsz; + + if (setsid() < 0) + err(1, "setsid"); + slave = open(ptsname(master), O_RDWR | O_NOCTTY); + if (slave < 0) + err(2, "open"); + /* Dereferences dangling t_pgrp pointer in the terminal. */ + memset(&winsz, 0xff, sizeof(winsz)); + if (ioctl(slave, TIOCSWINSZ, &winsz) < 0) + err(3, "ioctl(TIOCSWINSZ)"); + /* Dereferences dangling t_session pointer in the terminal. */ + if (ioctl(slave, TIOCSCTTY, 0) < 0) + err(4, "ioctl(TIOCSCTTY)"); + _exit(0); + } + + if (waitpid(child, &status, 0) < 0) + err(1, "waitpid"); + if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) + errx(1, "child exited with status %d", WEXITSTATUS(status)); +}home | help
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