[PATCH] r/o bind mounts: elevate write count for rmdir and unlink.

Elevate the write count during the vfs_rmdir() and vfs_unlink().

[AV: merged rmdir and unlink parts, added missing pieces in nfsd]

Acked-by: Serge Hallyn <serue@us.ibm.com>
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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -2190,7 +2190,12 @@ static long do_rmdir(int dfd, const char __user *pathname)
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
 		goto exit2;
+	error = mnt_want_write(nd.path.mnt);
+	if (error)
+		goto exit3;
 	error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
+	mnt_drop_write(nd.path.mnt);
+exit3:
 	dput(dentry);
 exit2:
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
@@ -2271,7 +2276,11 @@ static long do_unlinkat(int dfd, const char __user *pathname)
 		inode = dentry->d_inode;
 		if (inode)
 			atomic_inc(&inode->i_count);
+		error = mnt_want_write(nd.path.mnt);
+		if (error)
+			goto exit2;
 		error = vfs_unlink(nd.path.dentry->d_inode, dentry);
+		mnt_drop_write(nd.path.mnt);
 	exit2:
 		dput(dentry);
 	}

fs/nfsd/nfs4recover.c

@@ -46,6 +46,7 @@
 #include <linux/scatterlist.h>
 #include <linux/crypto.h>
 #include <linux/sched.h>
+#include <linux/mount.h>
 
 #define NFSDDBG_FACILITY                NFSDDBG_PROC
 
@@ -313,12 +314,17 @@ nfsd4_remove_clid_dir(struct nfs4_client *clp)
 	if (!rec_dir_init || !clp->cl_firststate)
 		return;
 
+	status = mnt_want_write(rec_dir.path.mnt);
+	if (status)
+		goto out;
 	clp->cl_firststate = 0;
 	nfs4_save_user(&uid, &gid);
 	status = nfsd4_unlink_clid_dir(clp->cl_recdir, HEXDIR_LEN-1);
 	nfs4_reset_user(uid, gid);
 	if (status == 0)
 		nfsd4_sync_rec_dir();
+	mnt_drop_write(rec_dir.path.mnt);
+out:
 	if (status)
 		printk("NFSD: Failed to remove expired client state directory"
 				" %.*s\n", HEXDIR_LEN, clp->cl_recdir);
@@ -347,13 +353,17 @@ nfsd4_recdir_purge_old(void) {
 
 	if (!rec_dir_init)
 		return;
+	status = mnt_want_write(rec_dir.path.mnt);
+	if (status)
+		goto out;
 	status = nfsd4_list_rec_dir(rec_dir.path.dentry, purge_old);
 	if (status == 0)
 		nfsd4_sync_rec_dir();
+	mnt_drop_write(rec_dir.path.mnt);
+out:
 	if (status)
 		printk("nfsd4: failed to purge old clients from recovery"
 			" directory %s\n", rec_dir.path.dentry->d_name.name);
-	return;
 }
 
 static int

fs/nfsd/vfs.c

@@ -1750,6 +1750,10 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 	if (!type)
 		type = rdentry->d_inode->i_mode & S_IFMT;
 
+	host_err = mnt_want_write(fhp->fh_export->ex_path.mnt);
+	if (host_err)
+		goto out_nfserr;
+
 	if (type != S_IFDIR) { /* It's UNLINK */
 #ifdef MSNFS
 		if ((fhp->fh_export->ex_flags & NFSEXP_MSNFS) &&
@@ -1765,10 +1769,12 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 	dput(rdentry);
 
 	if (host_err)
-		goto out_nfserr;
+		goto out_drop;
 	if (EX_ISSYNC(fhp->fh_export))
 		host_err = nfsd_sync_dir(dentry);
 
+out_drop:
+	mnt_drop_write(fhp->fh_export->ex_path.mnt);
 out_nfserr:
 	err = nfserrno(host_err);
 out:

ipc/mqueue.c

@@ -742,8 +742,11 @@ asmlinkage long sys_mq_unlink(const char __user *u_name)
 	inode = dentry->d_inode;
 	if (inode)
 		atomic_inc(&inode->i_count);
-
+	err = mnt_want_write(mqueue_mnt);
+	if (err)
+		goto out_err;
 	err = vfs_unlink(dentry->d_parent->d_inode, dentry);
+	mnt_drop_write(mqueue_mnt);
 out_err:
 	dput(dentry);