From patchwork Wed Mar 13 09:50:49 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paolo Pisati X-Patchwork-Id: 227220 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 45D3E2C029E for ; Wed, 13 Mar 2013 20:51:19 +1100 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1UFiL2-0001vU-O3; Wed, 13 Mar 2013 09:51:12 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1UFiKp-0001eS-2s for kernel-team@lists.ubuntu.com; Wed, 13 Mar 2013 09:50:59 +0000 Received: from 2-230-238-136.ip204.fastwebnet.it ([2.230.238.136] helo=canonical.com) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1UFiKo-0000u5-V6 for kernel-team@lists.ubuntu.com; Wed, 13 Mar 2013 09:50:59 +0000 From: Paolo Pisati To: kernel-team@lists.ubuntu.com Subject: [PATCH 09/11] UBUNTU: ubuntu: overlayfs -- fs: limit filesystem stacking depth Date: Wed, 13 Mar 2013 10:50:49 +0100 Message-Id: <1363168251-9374-10-git-send-email-paolo.pisati@canonical.com> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1363168251-9374-1-git-send-email-paolo.pisati@canonical.com> References: <1363168251-9374-1-git-send-email-paolo.pisati@canonical.com> X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com From: Miklos Szeredi Add a simple read-only counter to super_block that indicates deep this is in the stack of filesystems. Previously ecryptfs was the only stackable filesystem and it explicitly disallowed multiple layers of itself. Overlayfs, however, can be stacked recursively and also may be stacked on top of ecryptfs or vice versa. To limit the kernel stack usage we must limit the depth of the filesystem stack. Initially the limit is set to 2. Signed-off-by: Miklos Szeredi Signed-off-by: Andy Whitcroft (cherry picked from commit 69c1565cf4e8479ab7c5edf8ea194965376d04a8) BugLink: http://bugs.launchpad.net/bugs/1076317 Signed-off-by: Paolo Pisati --- fs/ecryptfs/main.c | 7 +++++++ fs/overlayfs/super.c | 10 ++++++++++ include/linux/fs.h | 11 +++++++++++ 3 files changed, 28 insertions(+) diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c index b4a6bef..703cda3 100644 --- a/fs/ecryptfs/main.c +++ b/fs/ecryptfs/main.c @@ -544,6 +544,13 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags s->s_maxbytes = path.dentry->d_sb->s_maxbytes; s->s_blocksize = path.dentry->d_sb->s_blocksize; s->s_magic = ECRYPTFS_SUPER_MAGIC; + s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1; + + rc = -EINVAL; + if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) { + printk(KERN_ERR "eCryptfs: maximum fs stacking depth exceeded\n"); + goto out_free; + } inode = ecryptfs_get_inode(path.dentry->d_inode, s); rc = PTR_ERR(inode); diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 71c2bce..6003393 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -553,6 +553,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) !S_ISDIR(lowerpath.dentry->d_inode->i_mode)) goto out_put_lowerpath; + sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth, + lowerpath.mnt->mnt_sb->s_stack_depth) + 1; + + err = -EINVAL; + if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) { + printk(KERN_ERR "overlayfs: maximum fs stacking depth exceeded\n"); + goto out_put_lowerpath; + } + + ufs->upper_mnt = clone_private_mount(&upperpath); err = PTR_ERR(ufs->upper_mnt); if (IS_ERR(ufs->upper_mnt)) { diff --git a/include/linux/fs.h b/include/linux/fs.h index 95ae38e..8d191b5 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -481,6 +481,12 @@ struct iattr { */ #include +/* + * Maximum number of layers of fs stack. Needs to be limited to + * prevent kernel stack overflow + */ +#define FILESYSTEM_MAX_STACK_DEPTH 2 + /** * enum positive_aop_returns - aop return codes with specific semantics * @@ -1461,6 +1467,11 @@ struct super_block { int cleancache_poolid; struct shrinker s_shrink; /* per-sb shrinker handle */ + + /* + * Indicates how deep in a filesystem stack this SB is + */ + int s_stack_depth; }; /* superblock cache pruning functions */