From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oa1-f72.google.com (mail-oa1-f72.google.com [209.85.160.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F1E118A6CF for ; Tue, 14 Apr 2026 01:32:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.72 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776130354; cv=none; b=hcz8MHbclS9sgmmeh3+TbL+MSVS5Q5egS+F3+hLrjjF/4RLFH7TKGLDV3QmwFwF47Qzr6ks5SjkaPm98EAW2id9b8sBa8kS991sZ3ZarQGlxfxN4UyZP5EeUcmar2GwYlB2yfLviAnr6qupk7Wjuw6L9laO+Izpsew2yb74r/3o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776130354; c=relaxed/simple; bh=+PS6A/P/x9NPo4+sWNIebEzHgbQEbCZFuuKN8qlLz+k=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=d4Q9KHTaJ9McmhqgPpOemz8g3oBlcJZ+2lUHP+ZMh0wzDcJimG5G0pIMzQCdfS1yKkV676/hUnj1TRIGxXuGoCBhwrFULuTvaPzd89RTS1AoID17O4yPCM23CNFaATg5d8LjSi1mv1Gq21QqDDi4RLC7Zxf/3ywMPca8Fzl3XSg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.160.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oa1-f72.google.com with SMTP id 586e51a60fabf-42343e87c3aso5343090fac.0 for ; Mon, 13 Apr 2026 18:32:33 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776130352; x=1776735152; h=content-transfer-encoding:to:from:subject:message-id:in-reply-to :date:mime-version:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=3phDk+POBrtCTEPoh3kuP2SDXTUtHrg2edX4uKz2Xug=; b=N7TCJsL9kwIVQENFvzvwpCC+nzDMBleJdLoZYtYEcW11ijm9kZMyGgQGif9wNd5IB0 WFQX66i1szxt8YKMeEp1vejwDdk8iivfkoJ7YSXjB9zhxdjRBkXp2k/mYn+sagIIECYW ACGybJSrfeTGQ7Ty/5Ql/7phzM03GtUyD6cRQCCf4NbRpJxaj0udmK3VeVROfSgfanz0 ZJC8cKFrtnHCxFAxKyE7Aa1cNVpoAmLZZMUrM1babxuHLLvV8Ntk8SyHtYNgb0lJNBu4 iR4UCo7NAGynLOD+K/ta5dYcFVPzq8mkQIVRd26MreNgusG5ICKSkeyL9KuXexi6Wry3 QBtA== X-Gm-Message-State: AOJu0YxN13vUgMyj7ypvmmDkCpMAtnZffg91x7rL0HwaVy1igwHILgVC wsJmkG0ySAcD63fxEe9v6ajX9BQaNGc0gI9rTMxGq/CeAjN7OHrTqvtMcSW6WEU3xAJ7VtskxUb mN0MBtCZzCggfZn04cfv9kAtZJHsNET7QrUyyKzzDROhpPonGa487ObX7Jtg= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:f009:b0:68c:3af3:6e60 with SMTP id 006d021491bc7-68c3af36f54mr6885819eaf.38.1776130352497; Mon, 13 Apr 2026 18:32:32 -0700 (PDT) Date: Mon, 13 Apr 2026 18:32:32 -0700 In-Reply-To: <69dd24f4.a00a0220.468cb.004a.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69dd9930.a00a0220.475f0.0030.GAE@google.com> Subject: Forwarded: [PATCH] drm/gem: fix use-after-free in drm_gem_release From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] drm/gem: fix use-after-free in drm_gem_release Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master KASAN reported a use-after-free in drm_gem_object_release_handle when drm_gem_release() races with drm_gem_handle_delete(). drm_gem_release() calls idr_for_each() which gives out object pointers, but a concurrent drm_gem_handle_delete() can free the object before drm_gem_object_release_handle() gets to use it. Fix this by splitting the operation into two phases: Phase 1: Walk the IDR under table_lock. For each object, atomically replace its IDR slot with NULL using idr_replace() so that a concurrent drm_gem_handle_delete() sees NULL and bails out with -EINVAL. Grab a reference on the object and collect it into a local list. Only atomic operations are performed here so holding a spinlock is safe. Phase 2: Outside the lock, iterate the local list and call drm_gem_object_release_handle() on each object safely. Drop our reference afterwards. Destroy the IDR only after all objects have been properly released. The idr_replace(NULL) in phase 1 is the key: it mirrors what drm_gem_handle_delete() itself does to atomically claim ownership of an object, ensuring that each object is processed by exactly one path. Reported-by: syzbot+b2e951687503f32f74ce@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Db2e951687503f32f74ce Signed-off-by: Deepanshu Kartikey --- drivers/gpu/drm/drm_gem.c | 49 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 48 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 891c3bff5ae0..9ec1f03c6383 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -1073,6 +1073,37 @@ drm_gem_open(struct drm_device *dev, struct drm_file= *file_private) spin_lock_init(&file_private->table_lock); } =20 +struct drm_gem_object_entry { + struct drm_gem_object *obj; + struct list_head head; +}; + +struct drm_gem_collect_data { + struct drm_file *file_priv; + struct list_head list; +}; + +static int drm_gem_object_collect(int id, void *ptr, void *data) +{ + struct drm_gem_collect_data *cd =3D data; + struct drm_gem_object_entry *entry; + struct drm_gem_object *obj; + + /* Atomically claim the slot =E2=86=92 handle_delete sees NULL, bails */ + obj =3D idr_replace(&cd->file_priv->object_idr, NULL, id); + if (IS_ERR_OR_NULL(obj)) + return 0; + + entry =3D kmalloc(sizeof(*entry), GFP_ATOMIC); + if (!entry) + return -ENOMEM; + + drm_gem_object_get(obj); + entry->obj =3D obj; + list_add(&entry->head, &cd->list); + return 0; +} + /** * drm_gem_release - release file-private GEM resources * @dev: drm_device which is being closed by userspace @@ -1085,8 +1116,24 @@ drm_gem_open(struct drm_device *dev, struct drm_file= *file_private) void drm_gem_release(struct drm_device *dev, struct drm_file *file_private) { + struct drm_gem_object_entry *entry, *tmp; + struct drm_gem_collect_data cd =3D { + .file_priv =3D file_private, + }; + INIT_LIST_HEAD(&cd.list); + + spin_lock(&file_private->table_lock); idr_for_each(&file_private->object_idr, - &drm_gem_object_release_handle, file_private); + &drm_gem_object_collect, &cd); + spin_unlock(&file_private->table_lock); + + list_for_each_entry_safe(entry, tmp, &cd.list, head) { + list_del(&entry->head); + drm_gem_object_release_handle(0, entry->obj, file_private); + drm_gem_object_put(entry->obj); + kfree(entry); + } + idr_destroy(&file_private->object_idr); } =20 --=20 2.43.0