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 <sprabhu@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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)) {