Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933705Ab3CMOSX (ORCPT ); Wed, 13 Mar 2013 10:18:23 -0400 Received: from mail-bk0-f45.google.com ([209.85.214.45]:39539 "EHLO mail-bk0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756430Ab3CMORK (ORCPT ); Wed, 13 Mar 2013 10:17:10 -0400 From: Miklos Szeredi To: viro@ZenIV.linux.org.uk, torvalds@linux-foundation.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, hch@infradead.org, akpm@linux-foundation.org, apw@canonical.com, nbd@openwrt.org, neilb@suse.de, jordipujolp@gmail.com, ezk@fsl.cs.sunysb.edu, dhowells@redhat.com, sedat.dilek@googlemail.com, hooanon05@yahoo.co.jp, mszeredi@suse.cz Subject: [PATCH 9/9] fs: limit filesystem stacking depth Date: Wed, 13 Mar 2013 15:16:33 +0100 Message-Id: <1363184193-1796-10-git-send-email-miklos@szeredi.hu> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1363184193-1796-1-git-send-email-miklos@szeredi.hu> References: <1363184193-1796-1-git-send-email-miklos@szeredi.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2974 Lines: 96 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 --- 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 e924cf4..8b0957e 100644 --- a/fs/ecryptfs/main.c +++ b/fs/ecryptfs/main.c @@ -567,6 +567,13 @@ 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) { + pr_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 6e0c0c2..482c26f 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -571,6 +571,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) } ufs->lower_namelen = statfs.f_namelen; + 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) { + pr_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 fd98a86..3353de6 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -244,6 +244,12 @@ 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 * @@ -1320,6 +1326,11 @@ struct super_block { /* Being remounted read-only */ int s_readonly_remount; + + /* + * Indicates how deep in a filesystem stack this SB is + */ + int s_stack_depth; }; /* superblock cache pruning functions */ -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/