[PATCH] Fix nfsd checking for read-only filesystem.

Currently nfsd only worries about read-only exports for
directories and files, which allows device special files
to be chmodded (for example).

This patch extends the test to cover all files, but is careful
to avoid it when an IRIX client is doing an write-permission test
against a pre-existing device special file.

fs/nfsd/nfsproc.c

@@ -250,11 +250,11 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
 					/* this is probably a permission check..
 					 * at least IRIX implements perm checking on
 					 *   echo thing > device-special-file-or-pipe
-					 * by does a CREATE with type==0
+					 * by doing a CREATE with type==0
 					 */
 					nfserr = nfsd_permission(newfhp->fh_export,
 								 newfhp->fh_dentry,
-								 MAY_WRITE);
+								 MAY_WRITE|MAY_LOCAL_ACCESS);
 					if (nfserr && nfserr != nfserr_rofs)
 						goto out_unlock;
 				}

fs/nfsd/vfs.c

@@ -1515,11 +1515,11 @@ nfsd_permission(struct svc_export *exp, struct dentry *dentry, int acc)
 		inode->i_uid, inode->i_gid, current->fsuid, current->fsgid);
 #endif
 
-	/* only care about readonly exports for files and
-	 * directories. links don't have meaningful write access,
-	 * and all else is local to the client
+	/* Normally we reject any write/sattr etc access on a read-only file
+	 * system.  But if it is IRIX doing check on write-access for a 
+	 * device special file, we ignore rofs.
 	 */
-	if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)) 
+	if (!(acc & MAY_LOCAL_ACCESS))
 		if (acc & (MAY_WRITE | MAY_SATTR | MAY_TRUNC)) {
 			if (EX_RDONLY(exp) || IS_RDONLY(inode))
 				return nfserr_rofs;

include/linux/nfsd/nfsd.h

@@ -38,7 +38,8 @@
 #define MAY_TRUNC		16
 #define MAY_LOCK		32
 #define MAY_OWNER_OVERRIDE	64
-#if (MAY_SATTR | MAY_TRUNC | MAY_LOCK | MAX_OWNER_OVERRIDE) & (MAY_READ | MAY_WRITE | MAY_EXEC | MAY_OWNER_OVERRIDE)
+#define	MAY_LOCAL_ACCESS	128 /* IRIX doing local access check on device special file*/
+#if (MAY_SATTR | MAY_TRUNC | MAY_LOCK | MAX_OWNER_OVERRIDE | MAY_LOCAL_ACCESS) & (MAY_READ | MAY_WRITE | MAY_EXEC | MAY_OWNER_OVERRIDE)
 # error "please use a different value for MAY_SATTR or MAY_TRUNC or MAY_LOCK or MAY_OWNER_OVERRIDE."
 #endif
 #define MAY_CREATE		(MAY_EXEC|MAY_WRITE)