linux-kernel - Re: [PATCH] signal: remove the wrong signal_pending() check in restore_user

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Message-ID: <20190604183523.kkruvskcgbli2fpu@dcvr>
Date:   Tue, 4 Jun 2019 18:35:23 +0000
From:   Eric Wong <e@...24.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        linux-kernel@...r.kernel.org, arnd@...db.de, dbueso@...e.de,
        axboe@...nel.dk, dave@...olabs.net, jbaron@...mai.com,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        omar.kilani@...il.com, tglx@...utronix.de, stable@...r.kernel.org,
        Al Viro <viro@...IV.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Laight <David.Laight@...LAB.COM>
Subject: Re: [PATCH] signal: remove the wrong signal_pending() check in
 restore_user_sigmask()

Oleg Nesterov <oleg@...hat.com> wrote:
> This is the minimal fix for stable, I'll send cleanups later.
> 
> The commit 854a6ed56839a40f6b5d02a2962f48841482eec4 ("signal: Add
> restore_user_sigmask()") introduced the visible change which breaks
> user-space: a signal temporary unblocked by set_user_sigmask() can
> be delivered even if the caller returns success or timeout.
> 
> Change restore_user_sigmask() to accept the additional "interrupted"
> argument which should be used instead of signal_pending() check, and
> update the callers.
> 
> Reported-by: Eric Wong <e@...24.org>
> Fixes: 854a6ed56839a40f6b5d02a2962f48841482eec4 ("signal: Add restore_user_sigmask()")
> cc: stable@...r.kernel.org (v5.0+)
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Thanks, for epoll_pwait on top of Linux v5.1.7 and cmogstored v1.7.0:

Tested-by: Eric Wong <e@...24.org>

(cmogstored v1.7.1 already works around this when it sees a 0
return value (but not >0, yet...))

> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 0fbb486..1147c5d 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2201,11 +2201,12 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>  	}
>  
>  	ret = wait_event_interruptible(ctx->wait, io_cqring_events(ring) >= min_events);
> -	if (ret == -ERESTARTSYS)
> -		ret = -EINTR;
>  
>  	if (sig)
> -		restore_user_sigmask(sig, &sigsaved);
> +		restore_user_sigmask(sig, &sigsaved, ret == -ERESTARTSYS);
> +
> +	if (ret == -ERESTARTSYS)
> +		ret = -EINTR;
>  
>  	return READ_ONCE(ring->r.head) == READ_ONCE(ring->r.tail) ? ret : 0;
>  }

That io_uring bit didn't apply cleanly to stable,
since stable is missing fdb288a679cdf6a71f3c1ae6f348ba4dae742681
("io_uring: use wait_event_interruptible for cq_wait conditional wait")
and related commits.

In any case, I'm not using io_uring anywhere, yet (and probably
won't, since I'll still need threads to deal with open/unlink/rename
on slow JBOD HDDs).