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 8340622FDE6 for ; Sun, 4 Oct 2026 21:02:15 +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=1791147736; cv=none; b=M4hmTigC1xMPeM7VSl1t++w9c5V8WzXNgRsaYIszsZM2zRaHyWSka7OLPUWUazsASlH0EubeVdKlW+5PTBT335ByvovdDx5hEzbr85OhQ0ZHFvgl9RXWP1stRt4W59zVVow5AhjpWr/jW+pADYXlVgcrRw3AxBiQpuUZBRcGABw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791147736; c=relaxed/simple; bh=zQhVPnjOmNU/bz91xAETPXxBk3PfaOxhqB3foISFvKU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=EkPNXvPfDlSsvJThWvWz37zElfca8XT/L/2gQz7eJaAH+tpyxdvR6o42bvcppeiRC/khSKUEfSltAKuZfBxIJGOHn12XKx/6zFBVGEv/s7mitXymdUEUS9FxUnIipT55/SC7W7vZ+HfCF0CzCPIQd2yqqSpgh80VH84jBvrsXNs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Tde+h9OT; 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="Tde+h9OT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91D171F000FF; Sun, 4 Oct 2026 21:02:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791147734; bh=/PlnVscxUUyVMFz/vHlUx3E9fZjpNOdxmGuUEiphRG8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Tde+h9OT621rgqHFu60bmXC0++Wdy7ayq4y/yfZ43MPdbQDxdZnXngZpq+6k9/axx SKbDXB2MeIPWd+n6ozynOSpYf1Tm7JpBhWteVaTgTqF1cbzrnmAw1QkXFIIeGksxnT DLRrNOS1QSiHb1DTRgBXiszL86+DyPJHCEkMxo4IekX//yRjWRsmMrNH/Ogrux5Boo qjp6BN727d+qZCGBGYSySvO/4oeZPZKfYLFwsX8APqS0KacB7tZPz64pZ92IviaFHA aD4XzviLLbbwOR+gzDjN08gY1ng+w9CKDA/5+nzPidgQ3WzrnO3zDADQK0vMl6r0cv GUE33o7+CT/OA== From: Sasha Levin To: stable@vger.kernel.org Cc: Yi Yang , stable@kernel.org, Greg Kroah-Hartman , Sasha Levin Subject: [PATCH 6.6.y] vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF Date: Sun, 4 Oct 2026 17:02:11 -0400 Message-ID: <20261004210031.1001408-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026100454-caloric-pried-9341@gregkh> References: <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=UTF-8 Content-Transfer-Encoding: 8bit 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(). [ sashal: REDUCED BACKPORT of 226bd5603371: carries 21/23 upstream changed lines; not carried: drivers/tty/vt/vc_screen.c:vcs_write() (partly) ] 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 [ sashal: Retained `ret = -ENXIO; goto unlock_out;` instead of upstream’s direct return to preserve explicit cleanup. ] Signed-off-by: Sasha Levin --- drivers/tty/vt/vc_screen.c | 25 +++++++++++++------------ 1 file changed, 13 insertions(+), 12 deletions(-) diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c index 5c417b6426bbf..a7b3fac5304d4 100644 --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c @@ -643,6 +643,19 @@ 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; + ret = -ENXIO; + goto unlock_out; + } + if (ret) { this_round -= ret; if (!this_round) { @@ -655,18 +668,6 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) goto unlock_out; } } - - /* 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; - ret = -ENXIO; - goto unlock_out; - } size = vcs_size(vc, attr, false); if (size < 0) { if (written) -- 2.53.0