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 599613DC4A0; Thu, 4 Jun 2026 06:54:32 +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=1780556074; cv=none; b=P0NzEk95Pamd9KbFdpkihi9bpwpX95SDPNDVb+iBoCt104KYwygySB9qhgPlmfovtQs8AlAhDRg0niaiUQ7hUAsxBpYHlQT5AhbAAn/DB8JHqNIGJfd9a2FKPAkmoBfDpTu8Arq5LGkftOoyvUahkpWGYWDy1OtV3XIUuCVGtzk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780556074; c=relaxed/simple; bh=t7wzq6SwHHzn7m7pUKVKyD/LXQvtEiqNndJ8YuiXegs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cZcO3Bf77uDs0dv8mqJYpNgvDdsSHDW6l+MEgkWMKhvLZB9M35a81X/ZQyAEkRu4MVPlc9OnOnMk61oS4eS0B/0/Lv2Y65TMUuEC05lhjAYpuEwgw9L5E9NY5I+4wOMt07F+E4dMCi/vVs4+99rjDkeqLlbUaY2iUUPORH1ZBjc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jaI/RHek; 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="jaI/RHek" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 945381F00893; Thu, 4 Jun 2026 06:54:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780556072; bh=GgVMlH4NEsyzxnB1xdRNm+DEWtAAcP1PE8YdWu5s0L0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jaI/RHekNfMp678FolEbAeKuPGG9bvWE1aLf9jyVzJAb+vHTVNc2wy/uytdho3b10 h0nbr2VQgaxzOIoVGLVwB5j/zlNjK/YmT++RmSNMzGOP3eAywYc6W/N47/zrqBlAPR ddivwAbP88M04e2UI2HTjjU+2xiCQJxyBGxuGQH1PR2s5bMY1QQFOc02lxcbS2WOHn pK7aVU3u8qBDCBDerB/79tm4d0sbrKgLgzJiqPlkKVKnTErFmOlW1ErYS7vSi4L7vz 9AdS3l7u+vy9Bfdz2P2WmpSHW1Xfpb5tWX3zLgaTNip8RpaDY3ItMNG41CSgrFAjYV qANuoLd5BGGrg== Message-ID: Date: Thu, 4 Jun 2026 08:54:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write To: Yi Yang , gregkh@linuxfoundation.org, kees@kernel.org, linux@weissschuh.net, george.kennedy@oracle.com Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, lujialin4@huawei.com References: <20260604060734.2914976-1-yiyang13@huawei.com> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 04. 06. 26, 8:07, Yi Yang wrote: > A KASAN null-ptr-deref was observed in vcs_notifier(): > > BUG: KASAN: null-ptr-deref in vcs_notifier+0x98/0x130 > Read of size 2 at addr qmp_cmd_name: qmp_capabilities, arguments: {} > > The issue is a race condition in vcs_write(). When the console_lock is > temporarily dropped (to copy data from userspace), the vc_data pointer > obtained from vcs_vc() may become stale. After re-acquiring the lock, > vcs_vc() is called again to re-validate the pointer. If the vc has been > deallocated in the meantime, vcs_vc() returns NULL, and the while loop > breaks (with written > 0). However, after the loop, vcs_scr_updated(vc) > is still called with the now-NULL vc pointer, leading to a null pointer > dereference in the notifier chain (vcs_notifier dereferences param->vc). > > Fix this by adding a NULL check for vc before calling vcs_scr_updated(). And vc is still protected by console_lock at that point. > Fixes: 8fb9ea65c9d1 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF") > Cc: stable@vger.kernel.org > Signed-off-by: Yi Yang Reviewed-by: Jiri Slaby > --- > drivers/tty/vt/vc_screen.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c > index 4d2d46c95fef..7d40eacc21b3 100644 > --- a/drivers/tty/vt/vc_screen.c > +++ b/drivers/tty/vt/vc_screen.c > @@ -686,7 +686,7 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) > } > *ppos += written; > ret = written; > - if (written) > + if (written && vc) > vcs_scr_updated(vc); > > return ret; -- js suse labs