From: Matt Fleming <matt@codeblueprint.co.uk>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-rt@vger.kernel.org, linux-kernel@vger.kernel.org,
Daniel Wagner <wagi@monom.org>,
Matt Fleming <matt@codeblueprint.co.uk>
Subject: [PATCH RT] signal: Prevent double-free of user struct
Date: Tue, 7 Apr 2020 10:54:13 +0100 [thread overview]
Message-ID: <20200407095413.30039-1-matt@codeblueprint.co.uk> (raw)
The way user struct reference counting works changed significantly with,
fda31c50292a ("signal: avoid double atomic counter increments for user accounting")
Now user structs are only freed once the last pending signal is
dequeued. Make sigqueue_free_current() follow this new convention to
avoid freeing the user struct multiple times and triggering this
warning:
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 6794 at lib/refcount.c:288 refcount_dec_not_one+0x45/0x50
Call Trace:
refcount_dec_and_lock_irqsave+0x16/0x60
free_uid+0x31/0xa0
? schedule_hrtimeout_range_clock+0x104/0x110
__dequeue_signal+0x17c/0x190
dequeue_signal+0x5a/0x1b0
do_sigtimedwait+0x208/0x250
__x64_sys_rt_sigtimedwait+0x6f/0xd0
do_syscall_64+0x72/0x200
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Reported-by: Daniel Wagner <wagi@monom.org>
---
kernel/signal.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 267fce07df5d..3651483bd4d8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -494,8 +494,8 @@ static void sigqueue_free_current(struct sigqueue *q)
up = q->user;
if (rt_prio(current->normal_prio) && !put_task_cache(current, q)) {
- atomic_dec(&up->sigpending);
- free_uid(up);
+ if (atomic_dec_and_test(&up->sigpending))
+ free_uid(up);
} else
__sigqueue_free(q);
}
--
2.16.4
next reply other threads:[~2020-04-07 9:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-07 9:54 Matt Fleming [this message]
2020-04-15 16:46 ` [PATCH RT] signal: Prevent double-free of user struct Sebastian Andrzej Siewior
2020-04-15 19:05 ` Daniel Wagner
2020-04-16 8:05 ` Sebastian Andrzej Siewior
2020-04-07 14:45 Markus Elfring
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200407095413.30039-1-matt@codeblueprint.co.uk \
--to=matt@codeblueprint.co.uk \
--cc=bigeasy@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt@vger.kernel.org \
--cc=wagi@monom.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).