tty/n_hdlc: fix __might_sleep warning

BugLink: https://bugs.launchpad.net/bugs/1837664
commit fc01d8c61ce02c034e67378cd3e645734bc18c8c upstream.

Fix __might_sleep warning[1] in tty/n_hdlc.c read due to copy_to_user
call while current is TASK_INTERRUPTIBLE.  This is a false positive
since the code path does not depend on current state remaining
TASK_INTERRUPTIBLE.  The loop breaks out and sets TASK_RUNNING after
calling copy_to_user.

This patch supresses the warning by setting TASK_RUNNING before calling
copy_to_user.

[1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Reported-by: syzbot <syzbot+c244af085a0159d22879@syzkaller.appspotmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index 33ee831bbd4ecfe1fb3f58b4fd4f6235211c4e7c..6ad58d44109fe6432b9322cc21890098ad59d807 100644 (file)
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -597,6 +597,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
                                /* too large for caller's buffer */
                                ret = -EOVERFLOW;
                        } else {
+                               __set_current_state(TASK_RUNNING);
                                if (copy_to_user(buf, rbuf->buf, rbuf->count))
                                        ret = -EFAULT;
                                else