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 4A7E94F55B8; Tue, 13 Oct 2026 12:43:20 +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=1791895401; cv=none; b=PQzbZZ5J/7D6oMPHisl7/WAIH4J0Wrcv6Q26e+7rNauJ7ClQUw52NaWq3HkkqMoyKmb8Lmra61KfSdc3lLnBzh+RWCpWlqVyNaTSKRG0qZ0FyMQWS1v4HXe5TxMJRtpYb2jtgCZyGyJPp6KbUPc/oY1CC+lCTpQ3112/HE7PciM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791895401; c=relaxed/simple; bh=2fLrYoylj7h4dWI48DcD+b8Szq2n5fi9+UOfP0Bc5og=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=fFvtByMkal8HbzDS1C9mUwy3xvU1ZPyXyvNHd/qlR+Mzf37vfqy/ivUKwQeBlTsnr/t1zJEHpWoEVOXTeGXXQaIWMAY/IPxJTfurMqSP1ZgYaO4MNwafPSMyJlQhXRKUvmIXinHuDkjP73o6YgkiSQa+T0XaSYIsRvPq5LSc0LM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=MUY9B861; 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="MUY9B861" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 623E01F000FF; Tue, 13 Oct 2026 12:43:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791895400; bh=s5YSzJPW9UNOyMUmvavkEWo4yrkZblsLp3RD6HSawuE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MUY9B861tIFUoIcGKixUly00CkfEx2V2cvvpidg5Fx66vsyrLEZp+UPLU7EImpYxV 11mcPxBipkuLIkroJ73Lxxp7S+E5Xb2rQQWlZmkU1uh+J7RIvRnUIuwQhQJJXrNDTu OFGs0MlQfkeHHOZPNV1QR1igxzSmBsYPP5+lL6+Q= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable@kernel.org, Yi Yang , Sasha Levin Subject: [PATCH 6.12 261/497] vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF Date: Tue, 13 Oct 2026 13:37:08 +0200 Message-ID: <20261013112914.085012912@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112907.864180619@linuxfoundation.org> References: <20261013112907.864180619@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yi Yang [ Upstream commit 226bd5603371cd9f6642cbb9e9a677f445de3530 ] 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 Signed-off-by: Sasha Levin --- drivers/tty/vt/vc_screen.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c index a59d2006b1a99..508d43167deb2 100644 --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c @@ -638,6 +638,18 @@ 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) { @@ -649,17 +661,6 @@ 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) -- 2.53.0