This is a note to let you know that I've just added the patch titled
NFS: don't try to cross a mountpount when there isn't one there.
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: nfs-don-t-try-to-cross-a-mountpount-when-there-isn-t-one-there.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Mar 22 14:57:32 CET 2018
From: NeilBrown neilb@suse.com Date: Wed, 15 Mar 2017 12:40:44 +1100 Subject: NFS: don't try to cross a mountpount when there isn't one there.
From: NeilBrown neilb@suse.com
[ Upstream commit 99bbf6ecc694dfe0b026e15359c5aa2a60b97a93 ]
consider the sequence of commands: mkdir -p /import/nfs /import/bind /import/etc mount --bind / /import/bind mount --make-private /import/bind mount --bind /import/etc /import/bind/etc
exportfs -o rw,no_root_squash,crossmnt,async,no_subtree_check localhost:/ mount -o vers=4 localhost:/ /import/nfs ls -l /import/nfs/etc
You would not expect this to report a stale file handle. Yet it does.
The manipulations under /import/bind cause the dentry for /etc to get the DCACHE_MOUNTED flag set, even though nothing is mounted on /etc. This causes nfsd to call nfsd_cross_mnt() even though there is no mountpoint. So an upcall to mountd for "/etc" is performed.
The 'crossmnt' flag on the export of / causes mountd to report that /etc is exported as it is a descendant of /. It assumes the kernel wouldn't ask about something that wasn't a mountpoint. The filehandle returned identifies the filesystem and the inode number of /etc.
When this filehandle is presented to rpc.mountd, via "nfsd.fh", the inode cannot be found associated with any name in /etc/exports, or with any mountpoint listed by getmntent(). So rpc.mountd says the filehandle doesn't exist. Hence ESTALE.
This is fixed by teaching nfsd not to trust DCACHE_MOUNTED too much. It is just a hint, not a guarantee. Change nfsd_mountpoint() to return '1' for a certain mountpoint, '2' for a possible mountpoint, and 0 otherwise.
Then change nfsd_crossmnt() to check if follow_down() actually found a mountpount and, if not, to avoid performing a lookup if the location is not known to certainly require an export-point.
Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: J. Bruce Fields bfields@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/nfsd/vfs.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-)
--- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -92,6 +92,12 @@ nfsd_cross_mnt(struct svc_rqst *rqstp, s err = follow_down(&path); if (err < 0) goto out; + if (path.mnt == exp->ex_path.mnt && path.dentry == dentry && + nfsd_mountpoint(dentry, exp) == 2) { + /* This is only a mountpoint in some other namespace */ + path_put(&path); + goto out; + }
exp2 = rqst_exp_get_by_name(rqstp, &path); if (IS_ERR(exp2)) { @@ -165,16 +171,26 @@ static int nfsd_lookup_parent(struct svc /* * For nfsd purposes, we treat V4ROOT exports as though there was an * export at *every* directory. + * We return: + * '1' if this dentry *must* be an export point, + * '2' if it might be, if there is really a mount here, and + * '0' if there is no chance of an export point here. */ int nfsd_mountpoint(struct dentry *dentry, struct svc_export *exp) { - if (d_mountpoint(dentry)) + if (!d_inode(dentry)) + return 0; + if (exp->ex_flags & NFSEXP_V4ROOT) return 1; if (nfsd4_is_junction(dentry)) return 1; - if (!(exp->ex_flags & NFSEXP_V4ROOT)) - return 0; - return d_inode(dentry) != NULL; + if (d_mountpoint(dentry)) + /* + * Might only be a mountpoint in a different namespace, + * but we need to check. + */ + return 2; + return 0; }
__be32
Patches currently in stable-queue which might be from neilb@suse.com are
queue-4.4/md-raid10-wait-up-frozen-array-in-handle_write_completed.patch queue-4.4/nfs-don-t-try-to-cross-a-mountpount-when-there-isn-t-one-there.patch queue-4.4/md-raid10-skip-spare-disk-as-first-disk.patch