lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <345de429-a88b-7097-d177-adecf9fed342@I-love.SAKURA.ne.jp> Date: Sat, 27 Aug 2022 00:27:46 +0900 From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> To: Eric Van Hensbergen <ericvh@...il.com>, Latchesar Ionkov <lucho@...kov.net>, Dominique Martinet <asmadeus@...ewreck.org>, Christian Schoenebeck <linux_oss@...debyte.com> Cc: syzbot <syzbot+8b41a1365f1106fd0f33@...kaller.appspotmail.com>, v9fs-developer@...ts.sourceforge.net, syzkaller-bugs@...glegroups.com, netdev@...r.kernel.org Subject: [PATCH] 9p/trans_fd: always use O_NONBLOCK read/write syzbot is reporting hung task at p9_fd_close() [1], for p9_mux_poll_stop() from p9_conn_destroy() from p9_fd_close() is failing to interrupt already started kernel_read() from p9_fd_read() from p9_read_work() and/or kernel_write() from p9_fd_write() from p9_write_work() requests. Since p9_socket_open() sets O_NONBLOCK flag, p9_mux_poll_stop() does not need to interrupt kernel_read()/kernel_write(). However, since p9_fd_open() does not set O_NONBLOCK flag, but pipe blocks unless signal is pending, p9_mux_poll_stop() needs to interrupt kernel_read()/kernel_write() when the file descriptor refers to a pipe. In other words, pipe file descriptor needs to be handled as if socket file descriptor. We somehow need to interrupt kernel_read()/kernel_write() on pipes. A minimal change, which this patch is doing, is to set O_NONBLOCK flag from p9_fd_open(), for O_NONBLOCK flag does not affect reading/writing of regular files. But this approach changes O_NONBLOCK flag on userspace- supplied file descriptors (which might break userspace programs), and O_NONBLOCK flag could be changed by userspace. It would be possible to set O_NONBLOCK flag every time p9_fd_read()/p9_fd_write() is invoked, but still remains small race window for clearing O_NONBLOCK flag. If we don't want to manipulate O_NONBLOCK flag, we might be able to surround kernel_read()/kernel_write() with set_thread_flag(TIF_SIGPENDING) and recalc_sigpending(). Since p9_read_work()/p9_write_work() works are processed by kernel threads which process global system_wq workqueue, signals could not be delivered from remote threads when p9_mux_poll_stop() from p9_conn_destroy() from p9_fd_close() is called. Therefore, calling set_thread_flag(TIF_SIGPENDING)/recalc_sigpending() every time would be needed if we count on signals for making kernel_read()/kernel_write() non-blocking. Link: https://syzkaller.appspot.com/bug?extid=8b41a1365f1106fd0f33 [1] Reported-by: syzbot <syzbot+8b41a1365f1106fd0f33@...kaller.appspotmail.com> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> Tested-by: syzbot <syzbot+8b41a1365f1106fd0f33@...kaller.appspotmail.com> --- Although syzbot tested that this patch solves hung task problem, syzbot cannot verify that this patch will not break functionality of p9 users. Please test before applying this patch. net/9p/trans_fd.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index e758978b44be..9870597da583 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -821,11 +821,13 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd) goto out_free_ts; if (!(ts->rd->f_mode & FMODE_READ)) goto out_put_rd; + ts->rd->f_flags |= O_NONBLOCK; ts->wr = fget(wfd); if (!ts->wr) goto out_put_rd; if (!(ts->wr->f_mode & FMODE_WRITE)) goto out_put_wr; + ts->wr->f_flags |= O_NONBLOCK; client->trans = ts; client->status = Connected; -- 2.18.4
Powered by blists - more mailing lists