On Jul 8, 2016, at 4:54 PM, J. Bruce Fields wrote: > On Thu, Jul 07, 2016 at 09:47:46PM -0400, Oleg Drokin wrote: >> It looks like we are bit overzealous about failing mkdir/create/mknod >> with permission denied if the parent dir is not writeable. >> Need to make sure the name does not exist first, because we need to >> return EEXIST in that case. >> >> Signed-off-by: Oleg Drokin <[email protected]> >> --- >> A very similar problem exists with symlinks, but the patch is more >> involved, so assuming this one is ok, I'll send a symlink one separately. >> fs/nfsd/nfs4proc.c | 6 +++++- >> fs/nfsd/vfs.c | 11 ++++++++++- >> 2 files changed, 15 insertions(+), 2 deletions(-) >> >> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c >> index de1ff1d..0067520 100644 >> --- a/fs/nfsd/nfs4proc.c >> +++ b/fs/nfsd/nfs4proc.c >> @@ -605,8 +605,12 @@ nfsd4_create(struct svc_rqst *rqstp, struct >> nfsd4_compound_state *cstate, >> >> fh_init(&resfh, NFS4_FHSIZE); >> >> + /* >> + * We just check thta parent is accessible here, nfsd_* do their >> + * own access permission checks >> + */ >> status = fh_verify(rqstp, &cstate->current_fh, S_IFDIR, >> - NFSD_MAY_CREATE); >> + NFSD_MAY_EXEC); >> if (status) >> return status; >> >> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c >> index 6fbd81e..6a45ec6 100644 >> --- a/fs/nfsd/vfs.c >> +++ b/fs/nfsd/vfs.c >> @@ -1161,7 +1161,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh >> *fhp, >> if (isdotent(fname, flen)) >> goto out; >> >> - err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE); >> + /* >> + * Even though it is a create, first we see if we are even allowed >> + * to peek inside the parent >> + */ >> + err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_EXEC); > > Looks like in the v3 case we haven't actually locked the directory yet > at this point so this check is a little race-prone.
In reality this check is not really needed, I suspect. When we call vfs_create/mknod/mkdir later on, it has it's own permission check anyway so if there was a race and somebody changed dir access in the middle, there's going to be another check anyway and it would be caught. Unless there's some weird server-side permission wiggling as well that makes it ineffective, but I imagine that one cannot really change in a racy way? > I wonder why the code's structured that way--it's confusing. Probably years of accumulated "damage" ;) > --b. > >> if (err) >> goto out; >> >> @@ -1211,6 +1215,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh >> *fhp, >> goto out; >> } >> >> + /* Now let's see if we actually have permissions to create */ >> + err = nfsd_permission(rqstp, fhp->fh_export, dentry, NFSD_MAY_CREATE); >> + if (err) >> + goto out; >> + >> if (!(iap->ia_valid & ATTR_MODE)) >> iap->ia_mode = 0; >> iap->ia_mode = (iap->ia_mode & S_IALLUGO) | type; >> -- >> 2.7.4
