From fb2088ccc139ffbf1cf359216883712dab4ae43d Mon Sep 17 00:00:00 2001 From: Sachin Prabhu Date: Mon, 1 Aug 2011 12:10:12 +0100 Subject: nfs: Do not allow multiple mounts on same mountpoint when using -o noac Do not allow multiple mounts on same mountpoint when using -o noac When you normally attempt to mount a share twice on the same mountpoint, a check in do_add_mount causes it to return an error # mount localhost:/nfsv3 /mnt # mount localhost:/nfsv3 /mnt mount.nfs: /mnt is already mounted or busy However when using the option 'noac', the user is able to mount the same share on the same mountpoint multiple times. This happens because a share mounted with the noac option is automatically assigned the 'sync' flag MS_SYNCHRONOUS in nfs_initialise_sb(). This flag is set after the check for already existing superblocks is done in sget(). The check for the mount flags in nfs_compare_mount_options() does not take into account the 'sync' flag applied later on in the code path. This means that when using 'noac', a new superblock structure is assigned for every new mount of the same share and multiple shares on the same mountpoint are allowed. ie. # mount -onoac localhost:/nfsv3 /mnt can be run multiple times. The patch checks for noac and assigns the sync flag before sget() is called to obtain an already existing superblock structure. Signed-off-by: Sachin Prabhu Reviewed-by: Jeff Layton Signed-off-by: Trond Myklebust --- fs/nfs/super.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) (limited to 'fs') diff --git a/fs/nfs/super.c b/fs/nfs/super.c index b961cea..9b7dd70 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -2035,9 +2035,6 @@ static inline void nfs_initialise_sb(struct super_block *sb) sb->s_blocksize = nfs_block_bits(server->wsize, &sb->s_blocksize_bits); - if (server->flags & NFS_MOUNT_NOAC) - sb->s_flags |= MS_SYNCHRONOUS; - sb->s_bdi = &server->backing_dev_info; nfs_super_set_maxbytes(sb, server->maxfilesize); @@ -2249,6 +2246,10 @@ static struct dentry *nfs_fs_mount(struct file_system_type *fs_type, if (server->flags & NFS_MOUNT_UNSHARED) compare_super = NULL; + /* -o noac implies -o sync */ + if (server->flags & NFS_MOUNT_NOAC) + sb_mntdata.mntflags |= MS_SYNCHRONOUS; + /* Get a superblock - note that we may end up sharing one that already exists */ s = sget(fs_type, compare_super, nfs_set_super, &sb_mntdata); if (IS_ERR(s)) { @@ -2361,6 +2362,10 @@ nfs_xdev_mount(struct file_system_type *fs_type, int flags, if (server->flags & NFS_MOUNT_UNSHARED) compare_super = NULL; + /* -o noac implies -o sync */ + if (server->flags & NFS_MOUNT_NOAC) + sb_mntdata.mntflags |= MS_SYNCHRONOUS; + /* Get a superblock - note that we may end up sharing one that already exists */ s = sget(&nfs_fs_type, compare_super, nfs_set_super, &sb_mntdata); if (IS_ERR(s)) { @@ -2628,6 +2633,10 @@ nfs4_remote_mount(struct file_system_type *fs_type, int flags, if (server->flags & NFS4_MOUNT_UNSHARED) compare_super = NULL; + /* -o noac implies -o sync */ + if (server->flags & NFS_MOUNT_NOAC) + sb_mntdata.mntflags |= MS_SYNCHRONOUS; + /* Get a superblock - note that we may end up sharing one that already exists */ s = sget(&nfs4_fs_type, compare_super, nfs_set_super, &sb_mntdata); if (IS_ERR(s)) { @@ -2916,6 +2925,10 @@ nfs4_xdev_mount(struct file_system_type *fs_type, int flags, if (server->flags & NFS4_MOUNT_UNSHARED) compare_super = NULL; + /* -o noac implies -o sync */ + if (server->flags & NFS_MOUNT_NOAC) + sb_mntdata.mntflags |= MS_SYNCHRONOUS; + /* Get a superblock - note that we may end up sharing one that already exists */ s = sget(&nfs4_fs_type, compare_super, nfs_set_super, &sb_mntdata); if (IS_ERR(s)) { @@ -3003,6 +3016,10 @@ nfs4_remote_referral_mount(struct file_system_type *fs_type, int flags, if (server->flags & NFS4_MOUNT_UNSHARED) compare_super = NULL; + /* -o noac implies -o sync */ + if (server->flags & NFS_MOUNT_NOAC) + sb_mntdata.mntflags |= MS_SYNCHRONOUS; + /* Get a superblock - note that we may end up sharing one that already exists */ s = sget(&nfs4_fs_type, compare_super, nfs_set_super, &sb_mntdata); if (IS_ERR(s)) { -- cgit v1.1