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author | Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> | 2022-08-26 18:27:46 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-11-25 19:45:56 +0300 |
commit | a8e2fc8f7b41fa9d9ca5f624f4e4d34fce5b40a9 (patch) | |
tree | e592c32e6325e14efe08a626b95866bc1317cca9 /net/9p/trans_fd.c | |
parent | a5da76df467a55071c88c7e2612250e91034e4d7 (diff) | |
download | linux-a8e2fc8f7b41fa9d9ca5f624f4e4d34fce5b40a9.tar.xz |
9p/trans_fd: always use O_NONBLOCK read/write
commit ef575281b21e9a34dfae544a187c6aac2ae424a9 upstream.
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://lkml.kernel.org/r/345de429-a88b-7097-d177-adecf9fed342@I-love.SAKURA.ne.jp
Link: https://syzkaller.appspot.com/bug?extid=8b41a1365f1106fd0f33 [1]
Reported-by: syzbot <syzbot+8b41a1365f1106fd0f33@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <syzbot+8b41a1365f1106fd0f33@syzkaller.appspotmail.com>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
[Dominique: add comment at Christian's suggestion]
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net/9p/trans_fd.c')
-rw-r--r-- | net/9p/trans_fd.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index c4096b14d159..fec6c800c898 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -821,11 +821,14 @@ 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; + /* prevent workers from hanging on IO when fd is a pipe */ + 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; |