From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793211152; b=EwL4YHsLgGI9GhUAltKJrM1EdIydMB2RvTU5pZZTyaU4z9dgpi9KfcdqozzW6M9Z6NSX 8S3o6FylZ7g8ld65W9/NNYHNDfbesLwRPkNWSdDxNNBGZ5lL2c2fmeksAwDBrVL0Bx7hI k5B3VpIuNzMPFE/EBSL9ltCg9IveS7rmYUSxGeP7KgRpW9h32c1e0RUe51t0jHGw+t4e5 x4VxD+18GyR+R7+i5oTyyvB6dXSD9kJXIlaHIEKFOk2arRRvjPb21Tog6/BD6VKBZJSOJ evM50N/fiPE4j39F3Yg7nZtMZW+dlwXsWAULS30peF080hcgJqEvEIOwVia4XWcuf3Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793211152; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=whcY1FG9Yaa0Z4HmxYiAm3eZ7+Bzf/XIrJ9VcoiWD3g=; b=WnnI1d7m8rz2f+Bq3ukP+mF9j6t1XhXoOPgWRrnA1o/y4WiTbos5QN7YMBwG6NEFDqZ1 JqBJplbzpwA0ruifWkOXnbvjC38pzLErnTKUJdvPOkswliVYohHLP0QDDkSa0S1MQcKcB iua1GcD05m+WI+nhDWq6BZ5B5gn86/nkJMgFF2kJ0y/7rbj2h+yb1ROCUMeYtprw+lTdK bVriDlet87UM+0xrGTPuG6ucmtr3rwiHtiW+3Qz/ytB9/fTQv2N29x5k3/NTD0SMCXKxN ++5Y74iv/qdo4G0vpePcxsbQxi5EZyhRkl5upjbUjHvT8oexn0lzooT7eYdPtDEE9pA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=MOy27Pao; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD0EE60A2603; Wed, 28 Oct 2026 18:12:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=MOy27Pao Received: by smtp.kernel.org (Postfix) with ESMTPSA id 276561F01825; Wed, 28 Oct 2026 18:12:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793211151; bh=whcY1FG9Yaa0Z4HmxYiAm3eZ7+Bzf/XIrJ9VcoiWD3g=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MOy27PaoEgsS3rz945qidTgyyVKOZkuBCkTp4zBD0tAg9iyseJL/rEBd2wDttzK9l TvY523l4qqkr70H7FwCFz6m6urVCGvCyW8WvNBEz5eKdJwfcNukbR0tavuBRHqw5WC Syd45icsTYYBmBvzsIKFNsIgIwDcYgf5LlDazEHs= 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 5.15 270/571] vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF Date: Wed, 28 Oct 2026 17:56:57 +0100 Message-ID: <20261028170014.408631837@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170008.009143722@linuxfoundation.org> References: <20261028170008.009143722@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-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 [ sashal: Replaced the direct -ENXIO return with a ret assignment and goto unlock_out. ] 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 27b44dc123859..22735ca14395a 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