[PATCH] r/o bind mounts: write counts for link/symlink

[AV: add missing nfsd pieces]
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -2387,7 +2387,12 @@ asmlinkage long sys_symlinkat(const char __user *oldname,
 	if (IS_ERR(dentry))
 		goto out_unlock;
 
+	error = mnt_want_write(nd.path.mnt);
+	if (error)
+		goto out_dput;
 	error = vfs_symlink(nd.path.dentry->d_inode, dentry, from, S_IALLUGO);
+	mnt_drop_write(nd.path.mnt);
+out_dput:
 	dput(dentry);
 out_unlock:
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
@@ -2482,7 +2487,12 @@ asmlinkage long sys_linkat(int olddfd, const char __user *oldname,
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
 		goto out_unlock;
+	error = mnt_want_write(nd.path.mnt);
+	if (error)
+		goto out_dput;
 	error = vfs_link(old_nd.path.dentry, nd.path.dentry->d_inode, new_dentry);
+	mnt_drop_write(nd.path.mnt);
+out_dput:
 	dput(new_dentry);
 out_unlock:
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);

fs/nfsd/vfs.c

@@ -1542,6 +1542,10 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (iap && (iap->ia_valid & ATTR_MODE))
 		mode = iap->ia_mode & S_IALLUGO;
 
+	host_err = mnt_want_write(fhp->fh_export->ex_path.mnt);
+	if (host_err)
+		goto out_nfserr;
+
 	if (unlikely(path[plen] != 0)) {
 		char *path_alloced = kmalloc(plen+1, GFP_KERNEL);
 		if (path_alloced == NULL)
@@ -1562,6 +1566,8 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	err = nfserrno(host_err);
 	fh_unlock(fhp);
 
+	mnt_drop_write(fhp->fh_export->ex_path.mnt);
+
 	cerr = fh_compose(resfhp, fhp->fh_export, dnew, fhp);
 	dput(dnew);
 	if (err==0) err = cerr;
@@ -1612,6 +1618,11 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
 	dold = tfhp->fh_dentry;
 	dest = dold->d_inode;
 
+	host_err = mnt_want_write(tfhp->fh_export->ex_path.mnt);
+	if (host_err) {
+		err = nfserrno(host_err);
+		goto out_dput;
+	}
 	host_err = vfs_link(dold, dirp, dnew);
 	if (!host_err) {
 		if (EX_ISSYNC(ffhp->fh_export)) {
@@ -1625,7 +1636,8 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
 		else
 			err = nfserrno(host_err);
 	}
-
+	mnt_drop_write(tfhp->fh_export->ex_path.mnt);
+out_dput:
 	dput(dnew);
 out_unlock:
 	fh_unlock(ffhp);