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 3727D64A8D for ; Sun, 4 Oct 2026 07:37:07 +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=1791099429; cv=none; b=NQVhlZFuX0ZSbxz5iHuapPXW8po4/Mr4yIMezJit2MF7eyDsJl9X/+p0njPEb8HG2wE4TslIUCUKPuyLHlq/JD99+46vjntOf2B6t8Yq+GxQefD77DJTTDoPaxOlmMGt4B3rBV6Mq8hN7TzSAmc/RXUBoc/P+BRM0D2jy78RGks= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791099429; c=relaxed/simple; bh=qb99d9UV38AeLbLWv6+l5TM5D7GA2W0s/CSf7LyW6iI=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=ggW4NSkzlFAlDzsq8iYDI87B9NWt+gO8wml+xvAlh/2q1vGFsH2ORiG1WD274tAQBSC1dv++vEHgNm2T1Qrx8BsSSzFSJg7JDrnwOSja2GttVa7drvtJQujBFR11pjUfKNgtv+Xn3GPh9+nl65b+yUdz1k+/Z4APodYXI5zTl14= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=YCNmtMlI; 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="YCNmtMlI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 344071F000FF; Sun, 4 Oct 2026 07:37:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791099427; bh=rFV6En+zxjAM/g45j5JdUi2rert2oR/pf9fnLf+IR+k=; h=Subject:To:Cc:From:Date; b=YCNmtMlI3jy2Vbf6eCUHt+jfi73e+tzqBrY8vbbDQBMwBNLnzOPqUleeDvIt+xrio 27QcBhQOjtEeRECnKUhHff+OVSu3NXJnuIDJCadBhlIcChpQyGB/CUXoRbQnMRR0QX IyceLgZY3Dx4cytAlYS5Xo/1ca3aKDXtQwZXueMw= Subject: FAILED: patch "[PATCH] vc_screen: reload vc pointer before if (ret) in vcs_write()" failed to apply to 6.6-stable tree To: yiyang13@huawei.com,gregkh@linuxfoundation.org Cc: From: Date: Sun, 04 Oct 2026 09:36:54 +0200 Message-ID: <2026100454-caloric-pried-9341@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 226bd5603371cd9f6642cbb9e9a677f445de3530 # git commit -s git send-email --to '' --in-reply-to '2026100454-caloric-pried-9341@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 226bd5603371cd9f6642cbb9e9a677f445de3530 Mon Sep 17 00:00:00 2001 From: Yi Yang Date: Tue, 1 Sep 2026 11:31:31 +0000 Subject: [PATCH] vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF The reload of 'vc' added by commit 8fb9ea65c9d1 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF") sits after the 'if (ret)' block, so the copy-failure break path exits the loop without reloading vc. If the vc was kfree()'d via vc_port_destruct during the unlocked copy_from_user() window, the post-loop 'if (written && vc) vcs_scr_updated(vc)' is reached with a stale non-NULL vc. The '&& vc' guard from commit a287620312dc ("vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write") only handles the NULL case, not this stale-non-NULL case; vcs_notifier() then reads param->vc->vc_num from freed memory: BUG: KASAN: slab-use-after-free in vcs_notifier+0x7c/0xd0 Read of size 2 at addr ffff888007149190 Call Trace: vcs_notifier+0x7c/0xd0 atomic_notifier_call_chain+0x70/0xa0 vcs_scr_updated+0x77/0xa0 vcs_write+0x71b/0x7e0 Allocated by task: vc_allocate -> con_install -> tty_open Freed by task: kfree <- vt_ioctl (VT_DISALLOCATE -> vc_port_destruct) Move the reload to immediately after console_lock(), before 'if (ret)', so every break path below passes a fresh vc to the post-loop vcs_scr_updated(). Fixes: a287620312dc ("vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write") Cc: stable@kernel.org Signed-off-by: Yi Yang Link: https://patch.msgid.link/20260901113131.2760010-1-yiyang13@huawei.com Signed-off-by: Greg Kroah-Hartman diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c index bf1502fd5bd4..79453abcf4d9 100644 --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c @@ -631,6 +631,18 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) ret = copy_from_user(con_buf, buf, this_round); console_lock(); + /* The vc might have been freed or vcs_size might have changed + * while we slept to grab the user buffer; recheck here, before + * if (ret), so every break path below passes a fresh vc to the + * post-loop vcs_scr_updated(). Return data written so far. + */ + vc = vcs_vc(inode, &viewed); + if (!vc) { + if (written) + break; + return -ENXIO; + } + if (ret) { this_round -= ret; if (!this_round) { @@ -642,17 +654,6 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) return -EFAULT; } } - - /* The vc might have been freed or vcs_size might have changed - * while we slept to grab the user buffer, so recheck. - * Return data written up to now on failure. - */ - vc = vcs_vc(inode, &viewed); - if (!vc) { - if (written) - break; - return -ENXIO; - } size = vcs_size(vc, attr, false); if (size < 0) { if (written)