git: 75a60b265825 - stable/12 - sigtimedwait: Use a unique wait channel for sleeping

[Mark Johnston]

The branch stable/12 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=75a60b2658254c974767a5407b9efbadd76ef017

commit 75a60b2658254c974767a5407b9efbadd76ef017
Author:     Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-08-16 17:15:25 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-08-23 00:43:16 +0000

    sigtimedwait: Use a unique wait channel for sleeping
    
    When a sigtimedwait(2) caller goes to sleep, it uses a wait channel of
    p->p_sigacts with the proc lock as the interlock.  However, p_sigacts
    can be shared between processes if a child is created with
    rfork(RFSIGSHARE | RFPROC).  Thus we can end up with two threads
    sleeping on the same wait channel using different locks, which is not
    permitted.
    
    Fix the problem simply by using a process-unique wait channel, following
    the example of sigsuspend.  The actual wait channel value is irrelevant
    here, sleeping threads are awoken using sleepq_abort().
    
    Reported by:    syzbot+8c417afabadb50bb8827 at syzkaller.appspotmail.com
    Reported by:    syzbot+1d89fc2a9ef92ef64fa8 at syzkaller.appspotmail.com
    Reviewed by:    kib
    Sponsored by:   The FreeBSD Foundation
    
    (cherry picked from commit c4feb1ab0ae0c0e779af372e4c5f3b9e0d3e1388)
---
 sys/kern/kern_sig.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 07102f6de5a5..917584a12b4b 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -1317,7 +1317,8 @@ kern_sigtimedwait(struct thread *td, sigset_t waitset, ksiginfo_t *ksi,
 			break;
 		}
 
-		error = msleep(ps, &p->p_mtx, PPAUSE|PCATCH, "sigwait", timo);
+		error = msleep(&p->p_sigacts, &p->p_mtx, PPAUSE | PCATCH,
+		    "sigwait", timo);
 
 		if (timeout != NULL) {
 			if (error == ERESTART) {