git: dab07b77a683 - stable/14 - procdesc: Make sure to drain selinfo sleepers in procdesc_free()
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Date: Wed, 20 May 2026 19:37:56 UTC
The branch stable/14 has been updated by markj:
URL: https://cgit.FreeBSD.org/src/commit/?id=dab07b77a683ef7fd3eb4d2ca8a99e2f3ed785d9
commit dab07b77a683ef7fd3eb4d2ca8a99e2f3ed785d9
Author: Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2026-05-08 13:03:49 +0000
Commit: Mark Johnston <markj@FreeBSD.org>
CommitDate: 2026-05-20 19:37:14 +0000
procdesc: Make sure to drain selinfo sleepers in procdesc_free()
Otherwise they are left on a freed list after procdesc_free() is called.
This can be exploited to elevate privileges.
Remove the PDF_SELECTED micro-optimization. doselwakeup() is a no-op if
no one ever called selrecord() on the file description, so I see no
reason to complicate the code to avoid the call.
Add some regression tests.
Approved by: so
Security: FreeBSD-SA-26:19.file
Security: CVE-2026-45251
Reported by: 75Acol, Lexpl0it, fcgboy, and robinzeng2015
Reviewed by: kib, oshogbo
Fixes: cfb5f7686588 ("Add experimental support for process descriptors")
Differential Revision: https://reviews.freebsd.org/D56887
---
sys/kern/sys_procdesc.c | 10 ++--
sys/sys/procdesc.h | 1 -
tests/sys/kern/Makefile | 2 +
tests/sys/kern/procdesc.c | 128 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 133 insertions(+), 8 deletions(-)
diff --git a/sys/kern/sys_procdesc.c b/sys/kern/sys_procdesc.c
index b2b638b6f99f..515d0365ec61 100644
--- a/sys/kern/sys_procdesc.c
+++ b/sys/kern/sys_procdesc.c
@@ -273,6 +273,7 @@ procdesc_free(struct procdesc *pd)
KASSERT((pd->pd_flags & PDF_CLOSED),
("procdesc_free: !PDF_CLOSED"));
+ seldrain(&pd->pd_selinfo);
knlist_destroy(&pd->pd_selinfo.si_note);
PROCDESC_LOCK_DESTROY(pd);
free(pd, M_PROCDESC);
@@ -315,10 +316,7 @@ procdesc_exit(struct proc *p)
procdesc_free(pd);
return (1);
}
- if (pd->pd_flags & PDF_SELECTED) {
- pd->pd_flags &= ~PDF_SELECTED;
- selwakeup(&pd->pd_selinfo);
- }
+ selwakeup(&pd->pd_selinfo);
KNOTE_LOCKED(&pd->pd_selinfo.si_note, NOTE_EXIT);
PROCDESC_UNLOCK(pd);
return (0);
@@ -433,10 +431,8 @@ procdesc_poll(struct file *fp, int events, struct ucred *active_cred,
PROCDESC_LOCK(pd);
if (pd->pd_flags & PDF_EXITED)
revents |= POLLHUP;
- if (revents == 0) {
+ else
selrecord(td, &pd->pd_selinfo);
- pd->pd_flags |= PDF_SELECTED;
- }
PROCDESC_UNLOCK(pd);
return (revents);
}
diff --git a/sys/sys/procdesc.h b/sys/sys/procdesc.h
index 81102dffa6ff..56d625950a80 100644
--- a/sys/sys/procdesc.h
+++ b/sys/sys/procdesc.h
@@ -86,7 +86,6 @@ struct procdesc {
* Flags for the pd_flags field.
*/
#define PDF_CLOSED 0x00000001 /* Descriptor has closed. */
-#define PDF_SELECTED 0x00000002 /* Issue selwakeup(). */
#define PDF_EXITED 0x00000004 /* Process exited. */
#define PDF_DAEMON 0x00000008 /* Don't exit when procdesc closes. */
diff --git a/tests/sys/kern/Makefile b/tests/sys/kern/Makefile
index 51d4aeeaedfc..c455b40747e8 100644
--- a/tests/sys/kern/Makefile
+++ b/tests/sys/kern/Makefile
@@ -27,6 +27,7 @@ ATF_TESTS_C+= ktls_test
.endif
ATF_TESTS_C+= ktrace_test
ATF_TESTS_C+= module_test
+ATF_TESTS_C+= procdesc
ATF_TESTS_C+= ptrace_test
TEST_METADATA.ptrace_test+= timeout="15"
ATF_TESTS_C+= reaper
@@ -89,6 +90,7 @@ LIBADD.unix_seqpacket_test+= pthread
LIBADD.kcov+= pthread
CFLAGS.ktls_test+= -DOPENSSL_API_COMPAT=0x10100000L
LIBADD.ktls_test+= crypto util
+LIBADD.procdesc+= pthread
LIBADD.socket_msg_waitall+= pthread
LIBADD.socket_splice+= pthread
LIBADD.sendfile_helper+= pthread
diff --git a/tests/sys/kern/procdesc.c b/tests/sys/kern/procdesc.c
new file mode 100644
index 000000000000..7505e0e4bb94
--- /dev/null
+++ b/tests/sys/kern/procdesc.c
@@ -0,0 +1,128 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2026 ConnectWise
+ * Copyright (c) 2026 Mark Johnston <markj@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <sys/user.h>
+#include <sys/proc.h>
+#include <sys/procdesc.h>
+#include <sys/sysctl.h>
+#include <sys/wait.h>
+
+#include <poll.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include <atf-c.h>
+
+/* Tests for procdesc(4) that aren't specific to any one syscall */
+
+static void *
+poll_procdesc(void *arg)
+{
+ struct pollfd pfd;
+
+ pfd.fd = *(int *)arg;
+ pfd.events = POLLHUP;
+ (void)poll(&pfd, 1, 5000);
+ return ((void *)(uintptr_t)pfd.revents);
+}
+
+/*
+ * Regression test to exercise the case where a procdesc is closed while a
+ * thread is poll()ing it.
+ */
+ATF_TC_WITHOUT_HEAD(poll_close_race);
+ATF_TC_BODY(poll_close_race, tc)
+{
+ pthread_t thr;
+ pid_t pid;
+ uintptr_t revents;
+ int error, pd;
+
+ pid = pdfork(&pd, PD_DAEMON);
+ ATF_REQUIRE_MSG(pid >= 0, "pdfork: %s", strerror(errno));
+ if (pid == 0) {
+ pause();
+ _exit(0);
+ }
+
+ error = pthread_create(&thr, NULL, poll_procdesc, &pd);
+ ATF_REQUIRE_MSG(error == 0, "pthread_create: %s", strerror(error));
+
+ /* Wait for the thread to block in poll(2). */
+ usleep(250000);
+
+ ATF_REQUIRE_MSG(close(pd) == 0, "close: %s", strerror(errno));
+
+ error = pthread_join(thr, (void *)&revents);
+ ATF_REQUIRE_MSG(error == 0, "pthread_join: %s", strerror(error));
+ ATF_REQUIRE_EQ(revents, POLLNVAL);
+}
+
+/*
+ * Verify that poll(2) of a procdesc returns POLLHUP when the process exits.
+ */
+ATF_TC_WITHOUT_HEAD(poll_exit_wakeup);
+ATF_TC_BODY(poll_exit_wakeup, tc)
+{
+ pthread_t thr;
+ uintptr_t revents;
+ pid_t pid;
+ int error, pd;
+
+ pid = pdfork(&pd, PD_DAEMON);
+ ATF_REQUIRE_MSG(pid >= 0, "pdfork: %s", strerror(errno));
+ if (pid == 0) {
+ pause();
+ _exit(0);
+ }
+
+ error = pthread_create(&thr, NULL, poll_procdesc, &pd);
+ ATF_REQUIRE_MSG(error == 0, "pthread_create: %s", strerror(error));
+
+ /* Wait for the thread to block in poll(2). */
+ usleep(250000);
+
+ ATF_REQUIRE_MSG(pdkill(pd, SIGKILL) == 0,
+ "pdkill: %s", strerror(errno));
+
+ error = pthread_join(thr, (void *)&revents);
+ ATF_REQUIRE_MSG(error == 0, "pthread_join: %s", strerror(error));
+ ATF_REQUIRE_EQ(revents, POLLHUP);
+
+ ATF_REQUIRE_MSG(close(pd) == 0, "close: %s", strerror(errno));
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+ ATF_TP_ADD_TC(tp, poll_close_race);
+ ATF_TP_ADD_TC(tp, poll_exit_wakeup);
+
+ return (atf_no_error());
+}