From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 38A98305679; Fri, 19 Jun 2026 20:47:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781902074; cv=none; b=Gf/fAh+aLbIIaFXb7xhytRsWhaB/Vo3gU+wlFu/473IwRoJeyPAdkQIoW3bGpsIbu3sLFJoDXdovl39v6KsEvlCwZXozwHah+B3Ca1Zqz5fKrj5DvcO8qFHjOBeHqpdYcP2+ru+i43EV7UeCtuZv27nimwOdE9tFgu5oWNtymEc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781902074; c=relaxed/simple; bh=ShzyKQcD/fORAt0e4n4OEY7UfiOZFwsOuiKAmPm5DdU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HIDqMU3whIWtSOucxQPysJn5sKOOZQchtBLVjS7/9Mjhvjs/mSuYhLpgz5eNJfQj7XK5rlN7BwBLOV6FHTc8/uFAFXHLXVE5Ii0fV4rDcY0FGM9fs7LCpROEs30KXlM8K0TaoXzsjIPPIIk7p98ciZyYLJ/hvlL98ZlRxRWf/QU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kMk3cXHu; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kMk3cXHu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E0EC1F000E9; Fri, 19 Jun 2026 20:47:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781902073; bh=oMepAgFoiMAcYRoSAIlQ6epWJLgq46cFe3AvDVMIw4U=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=kMk3cXHuC2lghPQeYaKjrO+oNMGuOOMBJQX+4oeTxGkw377PY59NPaA23oqbfGuMT s8VjPFh1iJVUgu0cptTommezQ5bAED7q3S5JzZVv8dezEdIKFpp//eJdwkAU55dCuR 4AF2BD5hWQhS1CThPPaCEFFO52iHTiPR84/R4YKmeWCKFVDdZzFTJnuu800VM6CUmg 3sWWyXkX94ExQ0d5XFQ/s1h+rCrBhbfJPd62CAci/NErzS1cPDsEZ5mm57jrvlCNP7 MLLiUD2zR4ZZOCpYjLpICPtQHYvVUxktXPQ476+NgD1N/7n7lfweaYtOXqpWH6j2ME FmjOIvYjqbiYw== Date: Fri, 19 Jun 2026 13:47:52 -0700 From: Kees Cook To: Oleg Nesterov Cc: Andrew Morton , Christian Brauner , Kusaram Devineni , Jens Axboe , linux-kernel@vger.kernel.org, io-uring@vger.kernel.org Subject: Re: [PATCH v2] signalfd: don't dequeue the forced fatal signals Message-ID: <202606191347.85254DD62@keescook> References: <202604052136.440E9CFA44@keescook> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jun 19, 2026 at 04:03:12PM +0200, Oleg Nesterov wrote: > It seems that this fix is going to be lost ;) Eek; thanks for the reminder. If Christian doesn't beat me to it, I'll grab this for -next after -rc2 so we can get some soak time. -Kees > > Can anyone pick it up? > > Oleg. > > On 04/06, Oleg Nesterov wrote: > > > > These signals should act like SIGKILL, in that userspace must never dequeue > > them. But as Kusaram explains, io_uring-driven signalfd_read_iter() called > > from get_signal() -> task_work_run() paths can do this before get_signal() > > has a chance to dequeue such a signal and notice SA_IMMUTABLE. > > > > Change signalfd_poll() and signalfd_dequeue() to add pending SA_IMMUTABLE > > signals to ctx->sigmask. > > > > TODO: we should probably change force_sig_info_to_task(HANDLER_EXIT) to > > make fatal_signal_pending() true, or add a fatal_or_forced_signal_pending() > > helper. Then signalfd_dequeue() could just return -EINTR in this case. > > This also makes sense for get_signal(), which could prioritize a fatal > > signal sent by (say) force_sig_seccomp(force_coredump => true), just like > > it already prioritizes SIGKILL. > > > > Cc: stable@kernel.org > > Reported-by: syzbot+0a4c46806941297fecb9@syzkaller.appspotmail.com > > Closes: https://syzkaller.appspot.com/bug?extid=0a4c46806941297fecb9 > > Tested-by: syzbot+0a4c46806941297fecb9@syzkaller.appspotmail.com > > Link: https://lore.kernel.org/all/69d122fd.050a0220.2dbe29.001c.GAE@google.com/ > > Suggested-by: Kusaram Devineni > > Signed-off-by: Oleg Nesterov > > Reviewed-by: Kees Cook > > --- > > fs/signalfd.c | 28 ++++++++++++++++++++++------ > > 1 file changed, 22 insertions(+), 6 deletions(-) > > > > diff --git a/fs/signalfd.c b/fs/signalfd.c > > index dff53745e352..22bc0870a824 100644 > > --- a/fs/signalfd.c > > +++ b/fs/signalfd.c > > @@ -48,17 +48,30 @@ static int signalfd_release(struct inode *inode, struct file *file) > > return 0; > > } > > > > +static void refine_sigmask(struct signalfd_ctx *ctx, sigset_t *sigmask) > > +{ > > + struct k_sigaction *k = current->sighand->action; > > + int n; > > + > > + *sigmask = ctx->sigmask; > > + for (n = 1; n <= _NSIG; ++n, ++k) { > > + if (k->sa.sa_flags & SA_IMMUTABLE) > > + sigaddset(sigmask, n); > > + } > > +} > > + > > static __poll_t signalfd_poll(struct file *file, poll_table *wait) > > { > > struct signalfd_ctx *ctx = file->private_data; > > __poll_t events = 0; > > + sigset_t sigmask; > > > > poll_wait(file, ¤t->sighand->signalfd_wqh, wait); > > > > spin_lock_irq(¤t->sighand->siglock); > > - if (next_signal(¤t->pending, &ctx->sigmask) || > > - next_signal(¤t->signal->shared_pending, > > - &ctx->sigmask)) > > + refine_sigmask(ctx, &sigmask); > > + if (next_signal(¤t->pending, &sigmask) || > > + next_signal(¤t->signal->shared_pending, &sigmask)) > > events |= EPOLLIN; > > spin_unlock_irq(¤t->sighand->siglock); > > > > @@ -155,11 +168,13 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info > > int nonblock) > > { > > enum pid_type type; > > - ssize_t ret; > > DECLARE_WAITQUEUE(wait, current); > > + sigset_t sigmask; > > + ssize_t ret; > > > > spin_lock_irq(¤t->sighand->siglock); > > - ret = dequeue_signal(&ctx->sigmask, info, &type); > > + refine_sigmask(ctx, &sigmask); > > + ret = dequeue_signal(&sigmask, info, &type); > > switch (ret) { > > case 0: > > if (!nonblock) > > @@ -174,7 +189,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info > > add_wait_queue(¤t->sighand->signalfd_wqh, &wait); > > for (;;) { > > set_current_state(TASK_INTERRUPTIBLE); > > - ret = dequeue_signal(&ctx->sigmask, info, &type); > > + ret = dequeue_signal(&sigmask, info, &type); > > if (ret != 0) > > break; > > if (signal_pending(current)) { > > @@ -184,6 +199,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info > > spin_unlock_irq(¤t->sighand->siglock); > > schedule(); > > spin_lock_irq(¤t->sighand->siglock); > > + refine_sigmask(ctx, &sigmask); > > } > > spin_unlock_irq(¤t->sighand->siglock); > > > > -- > > 2.52.0 > > > -- Kees Cook