From: J. Bruce Fields In the typical v2/v3 case the only new filehandles used as arguments to operations are filehandles taken directly off the wire, which don't get dentries until fh_verify() is called. But in v4 the filehandles that are arguments to operations were often created by previous operations (putrootfh, lookup, etc.) using fh_compose, which sets the dentry in the filehandle without calling nfsd_setuser(). This also means that, for example, if filesystem B is mounted on filesystem A, and filesystem A is exported without root-squashing, then a client can bypass the rootsquashing on B using a compound that starts at a filehandle in A, crosses into B using lookups, and then does stuff in B. Signed-off-by: J. Bruce Fields Signed-off-by: Neil Brown Signed-off-by: Andrew Morton --- fs/nfsd/nfsfh.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff -puN fs/nfsd/nfsfh.c~knfsd-nfsd-call-nfsd_setuser-on-fh_compose-fix-nfsd4-permissions-problem fs/nfsd/nfsfh.c --- a/fs/nfsd/nfsfh.c~knfsd-nfsd-call-nfsd_setuser-on-fh_compose-fix-nfsd4-permissions-problem +++ a/fs/nfsd/nfsfh.c @@ -187,13 +187,6 @@ fh_verify(struct svc_rqst *rqstp, struct goto out; } - /* Set user creds for this exportpoint */ - error = nfsd_setuser(rqstp, exp); - if (error) { - error = nfserrno(error); - goto out; - } - /* * Look up the dentry using the NFS file handle. */ @@ -251,6 +244,14 @@ fh_verify(struct svc_rqst *rqstp, struct } cache_get(&exp->h); + /* Set user creds for this exportpoint; necessary even in the "just + * checking" case because this may be a filehandle that was created by + * fh_compose, and that is about to be used in another nfsv4 compound + * operation */ + error = nfserrno(nfsd_setuser(rqstp, exp)); + if (error) + goto out; + error = nfsd_mode_check(rqstp, dentry->d_inode->i_mode, type); if (error) goto out; _