Re: [PATCH 22/26] sys_mknodat(): elevate write count for vfs_mknod/create()

[Dave Hansen <hansendc@us.ibm.com>]

On Sat, 2007-06-30 at 10:39 +0100, Christoph Hellwig wrote:
> On Mon, Jun 25, 2007 at 08:19:52AM -0700, Dave Hansen wrote:
> > > Should we just take the calls outside the switch statement? 
> > 
> > Yeah, that's much better.  I assume we don't care whether we're getting
> > -EROFS or -EPERM/-EINVAL for the S_IFDIR and default cases?
> 
> We need to keep the exact error returns, so you'll have to add some
> special case checks before the r/o check.  It's probably still cleaner,
> though.

How does this (untested) patch look?

--

This takes care of all of the direct callers of vfs_mknod().
Since a few of these cases also handle normal file creation
as well, this also covers some calls to vfs_create().

So that we don't have to make three mnt_want/drop_write()
calls inside of the switch statement, we move some of its
logic outside of the switch.

One thing I noticed: do we actually _need_ the first
S_ISDIR() check at the top of the function?  

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

 lxc-dave/fs/namei.c         |   29 ++++++++++++++++++++---------
 lxc-dave/fs/nfsd/vfs.c      |    8 ++++++--
 lxc-dave/net/unix/af_unix.c |    4 ++++
 3 files changed, 30 insertions(+), 11 deletions(-)

diff -puN fs/namei.c~18-24-sys-mknodat-elevate-write-count-for-vfs-mknod-create fs/namei.c
--- lxc/fs/namei.c~18-24-sys-mknodat-elevate-write-count-for-vfs-mknod-create	2007-07-05 15:40:18.000000000 -0700
+++ lxc-dave/fs/namei.c	2007-07-05 15:40:26.000000000 -0700
@@ -1911,13 +1911,27 @@ asmlinkage long sys_mknodat(int dfd, con
 	error = do_path_lookup(dfd, tmp, LOOKUP_PARENT, &nd);
 	if (error)
 		goto out;
+
 	dentry = lookup_create(&nd, 0);
 	error = PTR_ERR(dentry);
+	if (error)
+		goto out_unlock;
 
 	if (!IS_POSIXACL(nd.dentry->d_inode))
 		mode &= ~current->fs->umask;
-	if (!IS_ERR(dentry)) {
-		switch (mode & S_IFMT) {
+	if (S_ISDIR(mode)) {
+		error = -EPERM;
+		goto out_dput;
+	}
+	if (!S_ISREG(mode)  && !S_ISCHR(mode) && !S_ISBLK(mode) &&
+	    !S_ISFIFO(mode) && !S_ISSOCK(mode) && (mode != 0)) {
+		error = -EINVAL;
+		goto out_dput;
+	}
+	error = mnt_want_write(nd.mnt);
+	if (error)
+		goto out_dput;
+	switch (mode & S_IFMT) {
 		case 0: case S_IFREG:
 			error = vfs_create(nd.dentry->d_inode,dentry,mode,&nd);
 			break;
@@ -1928,14 +1942,11 @@ asmlinkage long sys_mknodat(int dfd, con
 		case S_IFIFO: case S_IFSOCK:
 			error = vfs_mknod(nd.dentry->d_inode,dentry,mode,0);
 			break;
-		case S_IFDIR:
-			error = -EPERM;
-			break;
-		default:
-			error = -EINVAL;
-		}
-		dput(dentry);
 	}
+	mnt_drop_write(nd.mnt);
+out_dput:
+	dput(dentry);
+out_unlock:
 	mutex_unlock(&nd.dentry->d_inode->i_mutex);
 	path_release(&nd);
 out:
diff -puN fs/nfsd/vfs.c~18-24-sys-mknodat-elevate-write-count-for-vfs-mknod-create fs/nfsd/vfs.c
--- lxc/fs/nfsd/vfs.c~18-24-sys-mknodat-elevate-write-count-for-vfs-mknod-create	2007-07-05 15:40:18.000000000 -0700
+++ lxc-dave/fs/nfsd/vfs.c	2007-07-05 15:40:18.000000000 -0700
@@ -1199,7 +1199,11 @@ nfsd_create(struct svc_rqst *rqstp, stru
 	case S_IFBLK:
 	case S_IFIFO:
 	case S_IFSOCK:
+		host_err = mnt_want_write(fhp->fh_export->ex_mnt);
+		if (host_err)
+			break;
 		host_err = vfs_mknod(dirp, dchild, iap->ia_mode, rdev);
+		mnt_drop_write(fhp->fh_export->ex_mnt);
 		break;
 	default:
 	        printk("nfsd: bad file type %o in nfsd_create\n", type);
@@ -1810,7 +1814,7 @@ nfsd_permission(struct svc_export *exp, 
 		inode->i_mode,
 		IS_IMMUTABLE(inode)?	" immut" : "",
 		IS_APPEND(inode)?	" append" : "",
-		__mnt_is_readonly(exp->mnt)?	" ro" : "");
+		__mnt_is_readonly(exp->ex_mnt)?	" ro" : "");
 	dprintk("      owner %d/%d user %d/%d\n",
 		inode->i_uid, inode->i_gid, current->fsuid, current->fsgid);
 #endif
@@ -1821,7 +1825,7 @@ nfsd_permission(struct svc_export *exp, 
 	 */
 	if (!(acc & MAY_LOCAL_ACCESS))
 		if (acc & (MAY_WRITE | MAY_SATTR | MAY_TRUNC)) {
-			if (EX_RDONLY(exp) || __mnt_is_readonly(exp->mnt))
+			if (EX_RDONLY(exp) || __mnt_is_readonly(exp->ex_mnt))
 				return nfserr_rofs;
 			if (/* (acc & MAY_WRITE) && */ IS_IMMUTABLE(inode))
 				return nfserr_perm;
diff -puN net/unix/af_unix.c~18-24-sys-mknodat-elevate-write-count-for-vfs-mknod-create net/unix/af_unix.c
--- lxc/net/unix/af_unix.c~18-24-sys-mknodat-elevate-write-count-for-vfs-mknod-create	2007-07-05 15:40:18.000000000 -0700
+++ lxc-dave/net/unix/af_unix.c	2007-07-05 15:40:18.000000000 -0700
@@ -815,7 +815,11 @@ static int unix_bind(struct socket *sock
 		 */
 		mode = S_IFSOCK |
 		       (SOCK_INODE(sock)->i_mode & ~current->fs->umask);
+		err = mnt_want_write(nd.mnt);
+		if (err)
+			goto out_mknod_dput;
 		err = vfs_mknod(nd.dentry->d_inode, dentry, mode, 0);
+		mnt_drop_write(nd.mnt);
 		if (err)
 			goto out_mknod_dput;
 		mutex_unlock(&nd.dentry->d_inode->i_mutex);
_