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 0B9D1246778 for ; Sun, 4 Oct 2026 17:39:06 +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=1791135548; cv=none; b=q5wvgP0G2HC6hRjqbqrLsFQPOKa7zsIpx0XvRLE00G9dA5nrMRtXjHylrXvGEC/tIKsNpWfWM455xDPZ/XunqlwkCTCbd+XznMIm06iEDYe9zit8M/qg9TyrfomFapPN/mUiPcqHuWZI9r/XwoN3gBdpXYfTrqnnx1xkNcwai3Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791135548; c=relaxed/simple; bh=W+9d9M1mJM/nuCzkO3Lhb3lXy1iC8mcaIQXvHXGHrVQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=g8cciyJ50zC1JMH7xOxyLlVqBhF6VGeRGOrkMQl4JFT/1uCkyRAqHSlLsMEKNPFjTZ6O5UKv82kfNp4eqnljzBhcrONFdFk0/hClrYPPK6PiciRJnmzpnWVoXoh+QxRWQ+52FC/0ulYWsGSXWyqSc9ClfDC0BoIv9s2hTkSeFeg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hHblCtD6; 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="hHblCtD6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7511D1F000FF; Sun, 4 Oct 2026 17:39:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791135546; bh=Y1O/M+Wq1fA5ogYsY/pnAJtxoIkhJiVTsQ/E/T86CKQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hHblCtD6J7H1DRezKAZK7CjkV1nPpvk1ZZVuzZS4NMeC0vqQ2UsA86yHbU/VgTTeo 7K/RCfwhLWvTYKAeaFa4ryUXyGe1hDvKZ3POPIh+8+R1UUI6C1JTv/Ep543KDBIrk8 boMduuiYNO1Jq1KH7myL2w6MeSELJpk4jsyXwrbUnKscE6RQcQoEa3AtMK1LLb/pSr mAAShxYDlvuMZW+SghUFQ9sECpyVHhK4Kj2GowY2SxICxq5ChcjQwGvpl220o6gZ6M W6D77a6zTl+HQBx/ncMe2JFILTXHqd6Vqe3nDiZ8i0tQbbrOheSvCbIbfwDR5bPZ3W kV6n+craa5Ghg== From: Sasha Levin To: stable@vger.kernel.org Cc: Yi Yang , stable@kernel.org, Greg Kroah-Hartman , Sasha Levin Subject: [PATCH 6.12.y 3/3] vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF Date: Sun, 4 Oct 2026 13:38:59 -0400 Message-ID: <20261004173840.989210-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261004173840.989210-1-sashal@kernel.org> References: <2026100453-thorn-hurricane-763b@gregkh> <20261004173840.989210-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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(). 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