Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932102Ab0DOXF0 (ORCPT ); Thu, 15 Apr 2010 19:05:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33992 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757871Ab0DOXFU (ORCPT ); Thu, 15 Apr 2010 19:05:20 -0400 From: Valerie Aurora To: Alexander Viro Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Valerie Aurora , Alexander Viro Subject: [PATCH 02/35] VFS: Add read-only users count to superblock Date: Thu, 15 Apr 2010 16:04:09 -0700 Message-Id: <1271372682-21225-3-git-send-email-vaurora@redhat.com> In-Reply-To: <1271372682-21225-2-git-send-email-vaurora@redhat.com> References: <1271372682-21225-1-git-send-email-vaurora@redhat.com> <1271372682-21225-2-git-send-email-vaurora@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4157 Lines: 128 While we can check if a file system is currently read-only, we can't guarantee that it will stay read-only. The file system can be remounted read-write at any time; it's also conceivable that a file system can be mounted a second time and converted to read-write if the underlying fs allows it. This is a problem for union mounts, which require the underlying file system be read-only. Add a read-only users count and don't allow remounts to change the file system to read-write or read-write mounts if there are any read-only users. Signed-off-by: Valerie Aurora Cc: Alexander Viro --- fs/namespace.c | 11 +++++++++++ fs/super.c | 23 +++++++++++++++++++++++ include/linux/fs.h | 8 ++++++++ 3 files changed, 42 insertions(+), 0 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 1cd59a0..9a40282 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -200,6 +200,17 @@ int __mnt_is_readonly(struct vfsmount *mnt) } EXPORT_SYMBOL_GPL(__mnt_is_readonly); +static void inc_hard_readonly_users(struct vfsmount *mnt) +{ + mnt->mnt_sb->s_hard_readonly_users++; +} + +static void dec_hard_readonly_users(struct vfsmount *mnt) +{ + BUG_ON(mnt->mnt_sb->s_hard_readonly_users == 0); + mnt->mnt_sb->s_hard_readonly_users--; +} + static inline void inc_mnt_writers(struct vfsmount *mnt) { #ifdef CONFIG_SMP diff --git a/fs/super.c b/fs/super.c index f35ac60..fa9b40b 100644 --- a/fs/super.c +++ b/fs/super.c @@ -117,6 +117,7 @@ out: */ static inline void destroy_super(struct super_block *s) { + BUG_ON(s->s_hard_readonly_users); security_sb_free(s); kfree(s->s_subtype); kfree(s->s_options); @@ -556,6 +557,21 @@ out: return err; } +/* + * Some uses of file systems require that they never be mounted + * read-write anywhere (e.g., the lower layers of union mounts must + * always be read-only). If there are any of these "hard" read-only + * mounts, don't permit a transition to read-write. + * + * Must be called while holding the namespace lock. + */ + +int sb_is_hard_readonly(struct super_block *sb) +{ + return sb->s_hard_readonly_users ? 1 : 0; +} +EXPORT_SYMBOL(sb_is_hard_readonly); + /** * do_remount_sb - asks filesystem to change mount options. * @sb: superblock in question @@ -598,6 +614,9 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force) return -EBUSY; } + if (remount_rw && sb_is_hard_readonly(sb)) + return -EROFS; + if (sb->s_op->remount_fs) { retval = sb->s_op->remount_fs(sb, &flags, data); if (retval) @@ -969,6 +988,10 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void WARN((mnt->mnt_sb->s_maxbytes < 0), "%s set sb->s_maxbytes to " "negative value (%lld)\n", type->name, mnt->mnt_sb->s_maxbytes); + error = -EROFS; + if (!(flags & MS_RDONLY) && sb_is_hard_readonly(mnt->mnt_sb)) + goto out_sb; + mnt->mnt_mountpoint = mnt->mnt_root; mnt->mnt_parent = mnt; up_write(&mnt->mnt_sb->s_umount); diff --git a/include/linux/fs.h b/include/linux/fs.h index 10b8ded..234ebc2 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1383,6 +1383,13 @@ struct super_block { * generic_show_options() */ char *s_options; + + /* + * Some mounts require that the underlying file system never + * transition to read-write. They mark the sb itself as + * read-only. + */ + int s_hard_readonly_users; }; extern struct timespec current_fs_time(struct super_block *sb); @@ -1767,6 +1774,7 @@ extern int get_sb_nodev(struct file_system_type *fs_type, int (*fill_super)(struct super_block *, void *, int), struct vfsmount *mnt); void generic_shutdown_super(struct super_block *sb); +int sb_is_hard_readonly(struct super_block *sb); void kill_block_super(struct super_block *sb); void kill_anon_super(struct super_block *sb); void kill_litter_super(struct super_block *sb); -- 1.6.3.3 -- 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/