nfsd: Fix possible BUG_ON firing in set_change_info

If vfs_getattr in fill_post_wcc returns an error, we don't
set fh_post_change.
For NFSv4, this can result in set_change_info triggering a BUG_ON.
i.e. fh_post_saved being zero isn't really a bug.

So:
 - instead of BUGging when fh_post_saved is zero, just clear ->atomic.
 - if vfs_getattr fails in fill_post_wcc, take a copy of i_ctime anyway.
   This will be used i seg_change_info, but not overly trusted.
 - While we are there, remove the pointless 'if' statements in set_change_info.
   There is no harm setting all the values.
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs3xdr.c

@@ -260,9 +260,11 @@ void fill_post_wcc(struct svc_fh *fhp)
 	err = vfs_getattr(fhp->fh_export->ex_path.mnt, fhp->fh_dentry,
 			&fhp->fh_post_attr);
 	fhp->fh_post_change = fhp->fh_dentry->d_inode->i_version;
-	if (err)
+	if (err) {
 		fhp->fh_post_saved = 0;
-	else
+		/* Grab the ctime anyway - set_change_info might use it */
+		fhp->fh_post_attr.ctime = fhp->fh_dentry->d_inode->i_ctime;
+	} else
 		fhp->fh_post_saved = 1;
 }
 

fs/nfsd/xdr4.h

@@ -484,18 +484,17 @@ static inline bool nfsd4_not_cached(struct nfsd4_compoundres *resp)
 static inline void
 set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp)
 {
-	BUG_ON(!fhp->fh_pre_saved || !fhp->fh_post_saved);
-	cinfo->atomic = 1;
+	BUG_ON(!fhp->fh_pre_saved);
+	cinfo->atomic = fhp->fh_post_saved;
 	cinfo->change_supported = IS_I_VERSION(fhp->fh_dentry->d_inode);
-	if (cinfo->change_supported) {
-		cinfo->before_change = fhp->fh_pre_change;
-		cinfo->after_change = fhp->fh_post_change;
-	} else {
-		cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec;
-		cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec;
-		cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec;
-		cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec;
-	}
+
+	cinfo->before_change = fhp->fh_pre_change;
+	cinfo->after_change = fhp->fh_post_change;
+	cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec;
+	cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec;
+	cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec;
+	cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec;
+
 }
 
 int nfs4svc_encode_voidres(struct svc_rqst *, __be32 *, void *);