From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 20681C43602 for ; Thu, 2 Jul 2026 07:51:50 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6713910F1DB; Thu, 2 Jul 2026 07:51:36 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b="DEFWrcJq"; dkim-atps=neutral Received: from mail-lf1-f45.google.com (mail-lf1-f45.google.com [209.85.167.45]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6664010E3E2 for ; Wed, 1 Jul 2026 23:17:17 +0000 (UTC) Received: by mail-lf1-f45.google.com with SMTP id 2adb3069b0e04-5aec139da7eso3160e87.1 for ; Wed, 01 Jul 2026 16:17:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782947835; x=1783552635; darn=lists.freedesktop.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=/M9QqAmY7Pg8H8gQnrUHA/IfrEsurxPK03ttJdgNJSc=; b=DEFWrcJqSIcjit0AajYI/La95/6RY83qqs/pAIc/rNIZPhLjQDJ5HKLYsQoR7gDY+k BRIwZ+Y4ZGZHzDALDqbmzA/2jxKkP4AWgiJm1SJJYth2AwC2p72+OVzSMrbzWnwYaRp/ iBCXesGWB4kRVyLrzeD098WHxMGvBRHc5Pzq9+QXuHOLC0f2c3spKJD9gmVBCyfjvFxc HPWx4WP/J7GnNam6ozwJZ8CDLFBUgS9i/qej0CF50O5LqEUdS52pLLOtwt3Nu4gFkvCT G3JyXHort3GSyU7R1LhYsylaKTbKlG9gvNnSMmskbauee44eS6XZWu9RfEF9JefRW/HP 0TKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782947835; x=1783552635; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=/M9QqAmY7Pg8H8gQnrUHA/IfrEsurxPK03ttJdgNJSc=; b=JokJt2f7Xkrto7vMaxZZ7OlvfcG+zt0+NcE+FNLsu4nhXRPY3HjjQOAtEUFnsvBCyn jWnN7so66TFi5qR6p5WVzGX2j/v/cPvMm9C1gXrS1glNd78nMb+1iSgSgszCzO9BzsG+ nQQ1U2m5bV7E0EaQkLHMbj0dLilqj+BIcgZZCY7A3VfgFmM1NCfGSMaW4rkd0qoP6c9z xv3RDD3olvyweMAflSbhQ/UE4pL9VW5iY8LNmkSMv1QuOgg66wJnOJDXFcBxu1oOUkz/ kyIiPRpTK/TWhxs9IKXRT60O3yyI8btT+ImktXlcobLY7YTdf4kI7PCqU1TwhG2Qb1Vn 8fPw== X-Forwarded-Encrypted: i=1; AHgh+RqzJbgTg5mgsbhuKa5i5MJLZn2Ltq9PAg4bizacZygZ2yOsx5/k1tSRTp8d7Guna39nF6CcTocQGRs=@lists.freedesktop.org X-Gm-Message-State: AOJu0YzcxqKt1CSgDMN+q5IMg22omwBfBxxeRifsilWolDH0q0Db0NYd u/IZZMm90bK9axjkWWuHghIpWkx10NZHahSS+Q/bi2EumN+tQtlg1Gnn X-Gm-Gg: AfdE7cmWoNFMXQXqYZOzws9PXCsMYQpZdarxhfOX+n4O3NoHpYdKwuhWHxwNW+74ATF xpneJdlqA9WrJtSLOgIgCeiBZg9sUzilNjA6emN8v54VbATx0IAP1IMbQbNPG74tieU73+fKYpC +QpN2BfCcAa1K7R2GylbrBt1CXYIj8um13A0JvQfBpSkQld4BdkKqX9wRaRxvzOjg+RAXcEi+Pg jAixBRz7wANVs4ELT7zn7eZE3lCvxwSRix4AZ+uXz7UPfj5t1ZlxtvS3NBOF/HQ7oIQa5OJDggi cznKPtHRwBKtBtuiiW3Apu69ee6MsbMd83ZWDE5w0Kx2ECtdfzSfU1ERNJD8066NawQTkff2W7l 4YZxOO+qFrijqWpeAEBE8TIC2u+sOmBYTKLQh/4AJ/rY98yVILfmt1EX4zGIgCjYlA91/MwAc2h l6edGvXqYaUTnHpJh/h4fFaX9e3+J1Dwk= X-Received: by 2002:a05:6512:2286:b0:5ae:b6cf:c745 with SMTP id 2adb3069b0e04-5aec630a373mr908377e87.17.1782947835394; Wed, 01 Jul 2026 16:17:15 -0700 (PDT) Received: from localhost.localdomain ([2a01:4f9:2a:1c13::2]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5aec8991974sm308950e87.4.2026.07.01.16.17.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2026 16:17:13 -0700 (PDT) From: Melbin K Mathew To: deller@gmx.de Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Melbin K Mathew , stable@vger.kernel.org Subject: [PATCH v2 2/2] fbdev: serialize mode sysfs access with lock_fb_info() Date: Thu, 2 Jul 2026 01:17:06 +0200 Message-Id: <20260701231706.234715-3-mlbnkm1@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260701221757.231490-1-mlbnkm1@gmail.com> References: <20260701221757.231490-1-mlbnkm1@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Thu, 02 Jul 2026 07:51:30 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" show_mode(), show_modes(), and store_mode() access fb_info->modelist and fb_info->mode without holding lock_fb_info(). store_modes() takes lock_fb_info() while replacing the modelist and freeing the old one. A concurrent reader or writer can load a pointer to an old modelist entry before store_modes() frees it, then dereference freed memory or store a stale freed pointer in fb_info->mode. Take lock_fb_info() in show_mode(), show_modes(), and store_mode() to serialize with store_modes(). In show_mode(), copy the mode to the stack and format after dropping the lock. In store_mode(), split activate() into a _locked variant to avoid double-locking, and hold the locks for the modelist walk, mode conversion, activation, and fb_info->mode assignment together. Cc: stable@vger.kernel.org Signed-off-by: Melbin K Mathew --- drivers/video/fbdev/core/fbsysfs.c | 46 ++++++++++++++++++++++++------ 1 file changed, 38 insertions(+), 8 deletions(-) diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c index af21dc5052..d3d60c555b 100644 --- a/drivers/video/fbdev/core/fbsysfs.c +++ b/drivers/video/fbdev/core/fbsysfs.c @@ -12,19 +12,24 @@ #include "fb_internal.h" #include "fbcon.h" +static int activate_locked(struct fb_info *fb_info, + struct fb_var_screeninfo *var) +{ + var->activate |= FB_ACTIVATE_FORCE; + return fb_set_var_from_user(fb_info, var); +} + static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var) { int err; - var->activate |= FB_ACTIVATE_FORCE; console_lock(); lock_fb_info(fb_info); - err = fb_set_var_from_user(fb_info, var); + err = activate_locked(fb_info, var); unlock_fb_info(fb_info); console_unlock(); - if (err) - return err; - return 0; + + return err; } static int mode_string(char *buf, size_t size, unsigned int offset, @@ -65,6 +70,9 @@ static ssize_t store_mode(struct device *device, struct device_attribute *attr, memset(&var, 0, sizeof(var)); + console_lock(); + lock_fb_info(fb_info); + list_for_each_entry(modelist, &fb_info->modelist, list) { mode = &modelist->mode; i = mode_string(mstr, sizeof(mstr), 0, mode); @@ -72,12 +80,22 @@ static ssize_t store_mode(struct device *device, struct device_attribute *attr, var = fb_info->var; fb_videomode_to_var(&var, mode); - if ((err = activate(fb_info, &var))) + err = activate_locked(fb_info, &var); + if (err) { + unlock_fb_info(fb_info); + console_unlock(); return err; + } fb_info->mode = mode; + unlock_fb_info(fb_info); + console_unlock(); return count; } } + + unlock_fb_info(fb_info); + console_unlock(); + return -EINVAL; } @@ -85,11 +103,20 @@ static ssize_t show_mode(struct device *device, struct device_attribute *attr, char *buf) { struct fb_info *fb_info = dev_get_drvdata(device); + struct fb_videomode mode; + bool have_mode = false; - if (!fb_info->mode) + lock_fb_info(fb_info); + if (fb_info->mode) { + mode = *fb_info->mode; + have_mode = true; + } + unlock_fb_info(fb_info); + + if (!have_mode) return 0; - return mode_string(buf, PAGE_SIZE, 0, fb_info->mode); + return mode_string(buf, PAGE_SIZE, 0, &mode); } static ssize_t store_modes(struct device *device, @@ -137,12 +164,15 @@ static ssize_t show_modes(struct device *device, struct device_attribute *attr, const struct fb_videomode *mode; i = 0; + lock_fb_info(fb_info); list_for_each_entry(modelist, &fb_info->modelist, list) { mode = &modelist->mode; i += mode_string(buf, PAGE_SIZE, i, mode); if (i >= PAGE_SIZE - 1) break; } + unlock_fb_info(fb_info); + return i; } -- 2.39.5