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author | NeilBrown <neilb@suse.com> | 2017-03-15 12:40:44 +1100 |
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committer | J. Bruce Fields <bfields@redhat.com> | 2017-04-25 17:25:54 -0400 |
commit | 99bbf6ecc694dfe0b026e15359c5aa2a60b97a93 (patch) | |
tree | 2b58d5702d17326f54995cadb8d5b2f9c635da5c | |
parent | 2f10fdcb6a1c5f26246339d3b606131fae483c44 (diff) | |
download | linux-stable-99bbf6ecc694dfe0b026e15359c5aa2a60b97a93.tar.gz linux-stable-99bbf6ecc694dfe0b026e15359c5aa2a60b97a93.tar.bz2 linux-stable-99bbf6ecc694dfe0b026e15359c5aa2a60b97a93.zip |
NFS: don't try to cross a mountpount when there isn't one there.
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>
-rw-r--r-- | fs/nfsd/vfs.c | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 19d50f600e8d..04cafaa94bf7 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -94,6 +94,12 @@ nfsd_cross_mnt(struct svc_rqst *rqstp, struct dentry **dpp, 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)) { @@ -167,16 +173,26 @@ static int nfsd_lookup_parent(struct svc_rqst *rqstp, struct dentry *dparent, st /* * 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 |