From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757704Ab3DBWoy (ORCPT ); Tue, 2 Apr 2013 18:44:54 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:33139 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760939Ab3DBWMv (ORCPT ); Tue, 2 Apr 2013 18:12:51 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Anatol Pomozov , Al Viro , Linus Torvalds Subject: [ 080/124] loop: prevent bdev freeing while device in use Date: Tue, 2 Apr 2013 15:11:02 -0700 Message-Id: <20130402221113.417233666@linuxfoundation.org> X-Mailer: git-send-email 1.8.1.rc1.5.g7e0651a In-Reply-To: <20130402221104.163133110@linuxfoundation.org> References: <20130402221104.163133110@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Anatol Pomozov commit c1681bf8a7b1b98edee8b862a42c19c4e53205fd upstream. struct block_device lifecycle is defined by its inode (see fs/block_dev.c) - block_device allocated first time we access /dev/loopXX and deallocated on bdev_destroy_inode. When we create the device "losetup /dev/loopXX afile" we want that block_device stay alive until we destroy the loop device with "losetup -d". But because we do not hold /dev/loopXX inode its counter goes 0, and inode/bdev can be destroyed at any moment. Usually it happens at memory pressure or when user drops inode cache (like in the test below). When later in loop_clr_fd() we want to use bdev we have use-after-free error with following stack: BUG: unable to handle kernel NULL pointer dereference at 0000000000000280 bd_set_size+0x10/0xa0 loop_clr_fd+0x1f8/0x420 [loop] lo_ioctl+0x200/0x7e0 [loop] lo_compat_ioctl+0x47/0xe0 [loop] compat_blkdev_ioctl+0x341/0x1290 do_filp_open+0x42/0xa0 compat_sys_ioctl+0xc1/0xf20 do_sys_open+0x16e/0x1d0 sysenter_dispatch+0x7/0x1a To prevent use-after-free we need to grab the device in loop_set_fd() and put it later in loop_clr_fd(). The issue is reprodusible on current Linus head and v3.3. Here is the test: dd if=/dev/zero of=loop.file bs=1M count=1 while [ true ]; do losetup /dev/loop0 loop.file echo 2 > /proc/sys/vm/drop_caches losetup -d /dev/loop0 done [ Doing bdgrab/bput in loop_set_fd/loop_clr_fd is safe, because every time we call loop_set_fd() we check that loop_device->lo_state is Lo_unbound and set it to Lo_bound If somebody will try to set_fd again it will get EBUSY. And if we try to loop_clr_fd() on unbound loop device we'll get ENXIO. loop_set_fd/loop_clr_fd (and any other loop ioctl) is called under loop_device->lo_ctl_mutex. ] Signed-off-by: Anatol Pomozov Cc: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/block/loop.c | 9 ++++++++- fs/block_dev.c | 1 + 2 files changed, 9 insertions(+), 1 deletion(-) --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -917,6 +917,11 @@ static int loop_set_fd(struct loop_devic lo->lo_flags |= LO_FLAGS_PARTSCAN; if (lo->lo_flags & LO_FLAGS_PARTSCAN) ioctl_by_bdev(bdev, BLKRRPART, 0); + + /* Grab the block_device to prevent its destruction after we + * put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev). + */ + bdgrab(bdev); return 0; out_clr: @@ -1026,8 +1031,10 @@ static int loop_clr_fd(struct loop_devic memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE); memset(lo->lo_crypt_name, 0, LO_NAME_SIZE); memset(lo->lo_file_name, 0, LO_NAME_SIZE); - if (bdev) + if (bdev) { + bdput(bdev); invalidate_bdev(bdev); + } set_capacity(lo->lo_disk, 0); loop_sysfs_exit(lo); if (bdev) { --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -551,6 +551,7 @@ struct block_device *bdgrab(struct block ihold(bdev->bd_inode); return bdev; } +EXPORT_SYMBOL(bdgrab); long nr_blockdev_pages(void) {