vfs: replace calling i_op->readlink with vfs_readlink()

Also check d_is_symlink() in callers instead of inode->i_op->readlink
because following patches will allow NULL ->readlink for symlinks.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

fs/namei.c

@@ -4668,6 +4668,27 @@ int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
 }
 EXPORT_SYMBOL(generic_readlink);
 
+/**
+ * vfs_readlink - copy symlink body into userspace buffer
+ * @dentry: dentry on which to get symbolic link
+ * @buffer: user memory pointer
+ * @buflen: size of buffer
+ *
+ * Does not touch atime.  That's up to the caller if necessary
+ *
+ * Does not call security hook.
+ */
+int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen)
+{
+	struct inode *inode = d_inode(dentry);
+
+	if (!inode->i_op->readlink)
+		return -EINVAL;
+
+	return inode->i_op->readlink(dentry, buffer, buflen);
+}
+EXPORT_SYMBOL(vfs_readlink);
+
 /**
  * vfs_get_link - get symlink body
  * @dentry: dentry on which to get symbolic link

fs/nfsd/nfs4xdr.c

@@ -3576,10 +3576,10 @@ nfsd4_encode_readlink(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd
 	if (!p)
 		return nfserr_resource;
 	/*
-	 * XXX: By default, the ->readlink() VFS op will truncate symlinks
-	 * if they would overflow the buffer.  Is this kosher in NFSv4?  If
-	 * not, one easy fix is: if ->readlink() precisely fills the buffer,
-	 * assume that truncation occurred, and return NFS4ERR_RESOURCE.
+	 * XXX: By default, vfs_readlink() will truncate symlinks if they
+	 * would overflow the buffer.  Is this kosher in NFSv4?  If not, one
+	 * easy fix is: if vfs_readlink() precisely fills the buffer, assume
+	 * that truncation occurred, and return NFS4ERR_RESOURCE.
 	 */
 	nfserr = nfsd_readlink(readlink->rl_rqstp, readlink->rl_fhp,
 						(char *)p, &maxcount);

fs/nfsd/vfs.c

@@ -1451,7 +1451,6 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 __be32
 nfsd_readlink(struct svc_rqst *rqstp, struct svc_fh *fhp, char *buf, int *lenp)
 {
-	struct inode	*inode;
 	mm_segment_t	oldfs;
 	__be32		err;
 	int		host_err;
@@ -1463,10 +1462,9 @@ nfsd_readlink(struct svc_rqst *rqstp, struct svc_fh *fhp, char *buf, int *lenp)
 
 	path.mnt = fhp->fh_export->ex_path.mnt;
 	path.dentry = fhp->fh_dentry;
-	inode = d_inode(path.dentry);
 
 	err = nfserr_inval;
-	if (!inode->i_op->readlink)
+	if (!d_is_symlink(path.dentry))
 		goto out;
 
 	touch_atime(&path);
@@ -1475,7 +1473,7 @@ nfsd_readlink(struct svc_rqst *rqstp, struct svc_fh *fhp, char *buf, int *lenp)
 	 */
 
 	oldfs = get_fs(); set_fs(KERNEL_DS);
-	host_err = inode->i_op->readlink(path.dentry, (char __user *)buf, *lenp);
+	host_err = vfs_readlink(path.dentry, (char __user *)buf, *lenp);
 	set_fs(oldfs);
 
 	if (host_err < 0)

fs/stat.c

@@ -329,12 +329,14 @@ SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname,
 		struct inode *inode = d_backing_inode(path.dentry);
 
 		error = empty ? -ENOENT : -EINVAL;
-		if (inode->i_op->readlink) {
+		/*
+		 * AFS mountpoints allow readlink(2) but are not symlinks
+		 */
+		if (d_is_symlink(path.dentry) || inode->i_op->readlink) {
 			error = security_inode_readlink(path.dentry);
 			if (!error) {
 				touch_atime(&path);
-				error = inode->i_op->readlink(path.dentry,
-							      buf, bufsiz);
+				error = vfs_readlink(path.dentry, buf, bufsiz);
 			}
 		}
 		path_put(&path);

fs/xfs/xfs_ioctl.c

@@ -287,7 +287,7 @@ xfs_readlink_by_handle(
 		return PTR_ERR(dentry);
 
 	/* Restrict this handle operation to symlinks only. */
-	if (!d_inode(dentry)->i_op->readlink) {
+	if (!d_is_symlink(dentry)) {
 		error = -EINVAL;
 		goto out_dput;
 	}
@@ -297,7 +297,7 @@ xfs_readlink_by_handle(
 		goto out_dput;
 	}
 
-	error = d_inode(dentry)->i_op->readlink(dentry, hreq->ohandle, olen);
+	error = vfs_readlink(dentry, hreq->ohandle, olen);
 
  out_dput:
 	dput(dentry);

include/linux/fs.h

@@ -2935,6 +2935,7 @@ extern int vfs_lstat(const char __user *, struct kstat *);
 extern int vfs_fstat(unsigned int, struct kstat *);
 extern int vfs_fstatat(int , const char __user *, struct kstat *, int);
 extern const char *vfs_get_link(struct dentry *, struct delayed_call *);
+extern int vfs_readlink(struct dentry *, char __user *, int);
 
 extern int __generic_block_fiemap(struct inode *inode,
 				  struct fiemap_extent_info *fieinfo,