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 A9E2E381EA8 for ; Mon, 24 Aug 2026 18:10:18 +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=1787595019; cv=none; b=HIb3kUa3lmwdBhE2Dofr/zGX1KeISOChXO9T16mZO/AeK+pepjdCw+cLJNiQNGvj9g2VmuhqGI+LW5CDs1BKgZu4oegG6KzSvFHhFarZC4yvMJclt9VYoVBMuBCsRfICWwLSar/9QwFbN1vIGcm87KKCfsyYsilqhUJfNKXkmFA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787595019; c=relaxed/simple; bh=ZPqKgEwPAX+vRrNBanKs3rapNLJizSzTPklcNGpEKy4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Jry/0k3/BzyIF5cT/vPUfYtKgMLOCks9jL36zL3r1qjxm07EJRFGNeE+irk73tz7FAFkTFvX5XFn2NS+spN/cHBGQGDBKF9znfvacM8svFtX8eta+d7q56gVQyALBuOY4jZAO3YmZFgLHCKL2dsycuAI1uOHK6NZj+G2waZtCSs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cG/OUCU6; 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="cG/OUCU6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C9F81F000E9; Mon, 24 Aug 2026 18:10:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787595018; bh=RQUkC9oFopQOHam7DR8oqxdyGx3d3CnMnplPfaPimu4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cG/OUCU6DZZ6rwp0DsrNjg7ZwGI14w/sItKgcgud2RU63Ioo+V9YmvChIpNeqbJ24 iPOzcKObuNheo7vNaxzBzhLeDnVPZsQm1xV355mmgaKOZCxDSnqGJgTD1D2UtX/XkJ UdFtnRDdGeqnhpQyyL65F4Wsg0CgI8S9luIP8qbRDsMGHJbTiDwCOKc2XIELDFnjV/ mrFGyVB3ebz0+6kqtSaDuLuyM58ZiPni/bFllhsdYfQCinM/1owJ/bJNV1oqWErpgQ 4tZE0pGyg/Xb9RH86LPrXQJ5S7AL5Y9Kg9fYgpYYcTkQIMM8tMn0cTZNkK4KevPHxN U3t4yDJMT37SA== From: Sasha Levin To: stable@vger.kernel.org Cc: Melbin K Mathew , Helge Deller , Sasha Levin Subject: [PATCH 7.1.y 2/2] fbdev: serialize mode sysfs access with lock_fb_info() Date: Mon, 24 Aug 2026 14:10:15 -0400 Message-ID: <20260824181015.254406-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260824181015.254406-1-sashal@kernel.org> References: <2026082036-chili-glider-8a45@gregkh> <20260824181015.254406-1-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: Melbin K Mathew [ Upstream commit 061db6b7a910b8378f3b2df64f8c0a3ddc6e85f2 ] 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 # v7.1+ Signed-off-by: Melbin K Mathew Signed-off-by: Helge Deller Signed-off-by: Sasha Levin --- 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 49d886c2dd7c8..c32dd71a38e1c 100644 --- a/drivers/video/fbdev/core/fbsysfs.c +++ b/drivers/video/fbdev/core/fbsysfs.c @@ -13,19 +13,24 @@ #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, @@ -66,6 +71,9 @@ 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); @@ -73,12 +81,22 @@ 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; } @@ -86,11 +104,20 @@ 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, @@ -138,12 +165,15 @@ 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; } -- 2.53.0