[PATCH] open returns ENFILE but creates file anyway

[Peter Staubach]

Hi.

When open(O_CREAT) is called and the error, ENFILE, is returned, the file
may be created anyway.  This is counter intuitive, against the SUS V3
specification, and may cause applications to misbehave if they are not
coded correctly to handle this semantic.  The SUS V3 specification 
explicitly
states "No files shall be created or modified if the function returns -1.".

The error, ENFILE, is used to indicate the system wide open file table is
full and no more file structs can be allocated.

This is due to an ordering problem.  The entry in the directory is created
before the file struct is allocated.  If the allocation for the file struct
fails, then the system call must return an error, but the directory entry
was already created and can not be safely removed.

The solution to this situation is relatively easy.  The file struct should
be allocated before the directory entry is created.  If the allocation 
fails,
then the error can be returned directly.  If the creation of the directory
entry fails, then the file struct can be easily freed.

   Thanx...

      ps

Signed-off-by: Peter Staubach <staubach@xxxxxxxxxx>
--- linux-2.6.12/fs/open.c.org	2005-08-24 10:51:00.000000000 -0400
+++ linux-2.6.12/fs/open.c	2005-08-24 11:28:59.000000000 -0400
@@ -741,6 +741,9 @@ asmlinkage long sys_fchown(unsigned int 
 	return error;
 }
 
+static struct file *__dentry_open(struct dentry *, struct vfsmount *, int,
+				struct file *);
+
 /*
  * Note that while the flag value (low two bits) for sys_open means:
  *	00 - read-only
@@ -759,6 +762,7 @@ struct file *filp_open(const char * file
 {
 	int namei_flags, error;
 	struct nameidata nd;
+	struct file *f;
 
 	namei_flags = flags;
 	if ((namei_flags+1) & O_ACCMODE)
@@ -766,10 +770,16 @@ struct file *filp_open(const char * file
 	if (namei_flags & O_TRUNC)
 		namei_flags |= 2;
 
+	error = -ENFILE;
+	f = get_empty_filp();
+	if (f == NULL)
+		return ERR_PTR(error);
+
 	error = open_namei(filename, namei_flags, mode, &nd);
 	if (!error)
-		return dentry_open(nd.dentry, nd.mnt, flags);
+		return __dentry_open(nd.dentry, nd.mnt, flags, f);
 
+	put_filp(f);
 	return ERR_PTR(error);
 }
 
@@ -777,14 +787,24 @@ EXPORT_SYMBOL(filp_open);
 
 struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
 {
-	struct file * f;
-	struct inode *inode;
 	int error;
+	struct file *f;
 
 	error = -ENFILE;
 	f = get_empty_filp();
-	if (!f)
-		goto cleanup_dentry;
+	if (f == NULL)
+		return ERR_PTR(error);
+
+	return __dentry_open(dentry, mnt, flags, f);
+}
+
+EXPORT_SYMBOL(dentry_open);
+
+static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags, struct file *f)
+{
+	struct inode *inode;
+	int error;
+
 	f->f_flags = flags;
 	f->f_mode = ((flags+1) & O_ACCMODE) | FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
 	inode = dentry->d_inode;
@@ -831,14 +851,11 @@ cleanup_all:
 	f->f_vfsmnt = NULL;
 cleanup_file:
 	put_filp(f);
-cleanup_dentry:
 	dput(dentry);
 	mntput(mnt);
 	return ERR_PTR(error);
 }
 
-EXPORT_SYMBOL(dentry_open);
-
 /*
  * Find an empty file descriptor entry, and mark it busy.
  */