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 D9AAF2D5412; Thu, 25 Jun 2026 13:08:35 +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=1782392916; cv=none; b=ZU9XRN/bx7kPujJ7GrNN7xxXl3wQtGBKbswwIHXvGD9s8fDsMvc9/qTDO1B6OKVx33Z8mk87kQK4GArv3OOK4kVOhq2cDcLc4JFrbcghdnMT8Iv/kEv0qK5+sZmeLkoNJvTJcEeVJtYvpq/Dh3e/UJUCQC5I3DJGTCEzH1N6Dj8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782392916; c=relaxed/simple; bh=uy5aw7NxE4B6ii8cqHzAbQKnAZmfhG1w8d1NJqDuYx0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YuBhraXvw2oxZynXi0MD5sDyU60VlVc0VWQbcryvlfy2bYFkHs9Whtrm9GilDB3DQO3JQ/mZYPi7I2yiS5rzVMOKaDyzJgrxayEeNG1M+D4948+6Vmgn/V0L3SKZeyK4O0pzXRfpgbC3nH7nstXLBVlIoxWDWqwIs4IfSbWSmQ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=i9UhukiZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="i9UhukiZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28DCC1F000E9; Thu, 25 Jun 2026 13:08:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1782392915; bh=ekNjmgVpYT8ImWK0zjCwqd2S/rXakdJ0eGhL3ptMjnk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=i9UhukiZ5DLPuqiMPmrSjpm0b6Wn3F4OhfufknzoA0ykAqax/VSh0VKtg8I6Pwv4i mboBHUpXG8SD/oKSqpZE2OJWD2USzsG8odkgvUksVP101SQw+8Secatu3C0wHWrGBy A1c6aML8lBmzmEDZ6RamxxL+KmVs2YTixtIl4Wv4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yi Yang , Jiri Slaby Subject: [PATCH 6.18 54/60] vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write Date: Thu, 25 Jun 2026 14:03:39 +0100 Message-ID: <20260625125653.615614718@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260625125645.554579168@linuxfoundation.org> References: <20260625125645.554579168@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yi Yang commit a287620312dc6dcb9a093417a0e589bf30fcf38a upstream. 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(). 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 Link: https://patch.msgid.link/20260604060734.2914976-1-yiyang13@huawei.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/vc_screen.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 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 } *ppos += written; ret = written; - if (written) + if (written && vc) vcs_scr_updated(vc); return ret;