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 8334C3A6EEE; Thu, 2 Jul 2026 16:26:53 +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=1783009616; cv=none; b=EEqIxElrQZb0wdM8rutBDV0Wswc6uqSrzUIW6vlpxtMupIVNA/eHbpzji2Pb6Mkv4wLdd2ocyD3/gSzz6uDoWxQOGj9HV2xxyldcU0fYjZrBxwZCMvgQmwcjHj4aNbJnueY8ja8k/6xAu7fBTtq+sXxdDt+vte7wjpmgbyggkOo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783009616; c=relaxed/simple; bh=fwBzhagYMv/sZI/q8KC/BLDnxtjCgixAs2cTwW8UhMU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hRJuoCM/XTYI0F+jw0nnW88VpEWV45uHostQyinuL9KfV4Ff6ckTN/PpBatzHdYKSw2Xo7D/a2yfjp/TrxbWuKkLTgqmJq/tWxe76qeCc7Wfmtc2kDXMgVGVPq0at7ASp42tloeopzOTLfT1TkIKajJNcK+vqwvcPwmUNpDAha4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=e2XU3TPr; 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="e2XU3TPr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5EE311F00A3A; Thu, 2 Jul 2026 16:26:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1783009612; bh=TKfI6Jz/cCTuLuPxVkMlzUgpLgkpgy6xby1fNH1zVmQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=e2XU3TPrasNY89Ydsa3sf8FFpr2R328tHgERnn0al9TDHI80q9aMXd4280YxAKZ+M knrRcEolzQtgDFvTR1RY+HU+ea/EUi1GoTIs82u+nDZ9DxCMCKG8OmPobj9+wZoPGr dGJn8/U1iy+4BwEZRwv3Ri/sn1J23NrF/Cv+aWJs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yi Yang , Jiri Slaby Subject: [PATCH 5.15 21/95] vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write Date: Thu, 2 Jul 2026 18:19:24 +0200 Message-ID: <20260702155109.654650021@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260702155109.196223802@linuxfoundation.org> References: <20260702155109.196223802@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yi Yang commit a287620312dc6dcb9a093417a0e589bf30fcf38a upstream. A KASAN null-ptr-deref was observed in vcs_notifier(): BUG: KASAN: null-ptr-deref in vcs_notifier+0x98/0x130 Read of size 2 at addr qmp_cmd_name: qmp_capabilities, arguments: {} The issue is a race condition in vcs_write(). When the console_lock is temporarily dropped (to copy data from userspace), the vc_data pointer obtained from vcs_vc() may become stale. After re-acquiring the lock, vcs_vc() is called again to re-validate the pointer. If the vc has been deallocated in the meantime, vcs_vc() returns NULL, and the while loop breaks (with written > 0). However, after the loop, vcs_scr_updated(vc) is still called with the now-NULL vc pointer, leading to a null pointer dereference in the notifier chain (vcs_notifier dereferences param->vc). Fix this by adding a NULL check for vc before calling vcs_scr_updated(). Fixes: 8fb9ea65c9d1 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF") Cc: stable@vger.kernel.org Signed-off-by: Yi Yang Reviewed-by: Jiri Slaby Link: https://patch.msgid.link/20260604060734.2914976-1-yiyang13@huawei.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/vc_screen.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c @@ -699,7 +699,7 @@ vcs_write(struct file *file, const char } *ppos += written; ret = written; - if (written) + if (written && vc) vcs_scr_updated(vc); unlock_out: