From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 ECFB83DC862; Tue, 12 May 2026 17:42:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778607728; cv=none; b=VHcFQCo7LHUzDa2iVttJiK07lJ7LVkznCMZOAz+KA8rjwggBGI6+3GSZ5Z+CONvYG+6qKJrFpF2AkmOPbyGEh43qqXNnd/rArZSoXsnfljEAfdAddXvx59aehb4BQvWZCA68/btTXZQgQL3wCobBfCfzgkxWHWP3crpn2neNHdg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778607728; c=relaxed/simple; bh=MPOph1mj9++h4qF8TzJVUCWrqhSw8XrQSna1VEn3F9I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tJk7pwWJUZq7UTHrGAV8Gso6Zx1NzkqloRMD76CWL5zJPXlClMPFY9889KZl0pC5KcVl1PsTlWtsCzExGlMuPJr0AiTkoy2WITwW/8DTuV8qQlhnjDI4wcvDYTgw5685K9WpCBfJ4KfrF9DarLyOaTGbJyCWymbZP1Cr9K86erY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=EE4gcOdR; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="EE4gcOdR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78818C2BCB0; Tue, 12 May 2026 17:42:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1778607727; bh=MPOph1mj9++h4qF8TzJVUCWrqhSw8XrQSna1VEn3F9I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EE4gcOdRXPQftl2cZ4+ZFcvrVuPrb1bZbE6zwCmTxcSRHQusMgBqV93vfPlVHi8xM 728pRQrH4oYeYyy79sPKiFlBhwwYBVC5GO8+qYilfGe1QkpqCnkDL/HBYeHvgf+f0g dWA7ERrYOWCZcaZJi1JZCJLWtdZSERI8BueZaCNQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Rajat Gupta , Helge Deller Subject: [PATCH 6.12 005/206] fbdev: udlfb: add vm_ops to dlfb_ops_mmap to prevent use-after-free Date: Tue, 12 May 2026 19:37:37 +0200 Message-ID: <20260512173932.931461941@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260512173932.810559588@linuxfoundation.org> References: <20260512173932.810559588@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rajat Gupta commit 8de779dc40d35d39fa07387b6f921eb11df0f511 upstream. dlfb_ops_mmap() uses remap_pfn_range() to map vmalloc framebuffer pages to userspace but sets no vm_ops on the VMA. This means the kernel cannot track active mmaps. When dlfb_realloc_framebuffer() replaces the backing buffer via FBIOPUT_VSCREENINFO, existing mmap PTEs are not invalidated. On USB disconnect, dlfb_ops_destroy() calls vfree() on the old pages while userspace PTEs still reference them, resulting in a use-after-free: the process retains read/write access to freed kernel pages. Add vm_operations_struct with open/close callbacks that maintain an atomic mmap_count on struct dlfb_data. In dlfb_realloc_framebuffer(), check mmap_count and return -EBUSY if the buffer is currently mapped, preventing buffer replacement while userspace holds stale PTEs. Tested with PoC using dummy_hcd + raw_gadget USB device emulation. Signed-off-by: Rajat Gupta Acked-by: Greg Kroah-Hartman Cc: stable@vger.kernel.org Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman --- drivers/video/fbdev/udlfb.c | 31 ++++++++++++++++++++++++++++++- include/video/udlfb.h | 1 + 2 files changed, 31 insertions(+), 1 deletion(-) --- a/drivers/video/fbdev/udlfb.c +++ b/drivers/video/fbdev/udlfb.c @@ -321,12 +321,32 @@ static int dlfb_set_video_mode(struct dl return retval; } +static void dlfb_vm_open(struct vm_area_struct *vma) +{ + struct dlfb_data *dlfb = vma->vm_private_data; + + atomic_inc(&dlfb->mmap_count); +} + +static void dlfb_vm_close(struct vm_area_struct *vma) +{ + struct dlfb_data *dlfb = vma->vm_private_data; + + atomic_dec(&dlfb->mmap_count); +} + +static const struct vm_operations_struct dlfb_vm_ops = { + .open = dlfb_vm_open, + .close = dlfb_vm_close, +}; + static int dlfb_ops_mmap(struct fb_info *info, struct vm_area_struct *vma) { unsigned long start = vma->vm_start; unsigned long size = vma->vm_end - vma->vm_start; unsigned long offset = vma->vm_pgoff << PAGE_SHIFT; unsigned long page, pos; + struct dlfb_data *dlfb = info->par; if (info->fbdefio) return fb_deferred_io_mmap(info, vma); @@ -358,6 +378,9 @@ static int dlfb_ops_mmap(struct fb_info size = 0; } + vma->vm_ops = &dlfb_vm_ops; + vma->vm_private_data = dlfb; + atomic_inc(&dlfb->mmap_count); return 0; } @@ -1176,7 +1199,6 @@ static void dlfb_deferred_vfree(struct d /* * Assumes &info->lock held by caller - * Assumes no active clients have framebuffer open */ static int dlfb_realloc_framebuffer(struct dlfb_data *dlfb, struct fb_info *info, u32 new_len) { @@ -1188,6 +1210,13 @@ static int dlfb_realloc_framebuffer(stru new_len = PAGE_ALIGN(new_len); if (new_len > old_len) { + if (atomic_read(&dlfb->mmap_count) > 0) { + dev_warn(info->dev, + "refusing realloc: %d active mmaps\n", + atomic_read(&dlfb->mmap_count)); + return -EBUSY; + } + /* * Alloc system memory for virtual framebuffer */ --- a/include/video/udlfb.h +++ b/include/video/udlfb.h @@ -56,6 +56,7 @@ struct dlfb_data { spinlock_t damage_lock; struct work_struct damage_work; struct fb_ops ops; + atomic_t mmap_count; /* blit-only rendering path metrics, exposed through sysfs */ atomic_t bytes_rendered; /* raw pixel-bytes driver asked to render */ atomic_t bytes_identical; /* saved effort with backbuffer comparison */