fs/9p: setrlimit fix for 9p write

Current 9p client file write code does not check for RLIMIT_FSIZE resource.
This bug was found by running LTP test case for setrlimit. This bug is fixed
by calling generic_write_checks before sending the write request to the
server.
Without this patch: the write function is allowed to write above the
RLIMIT_FSIZE set by user.
With this patch: the write function checks for RLIMIT_SIZE and writes upto
the size limit.
Signed-off-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

fs/9p/vfs_file.c

@@ -219,7 +219,9 @@ static ssize_t
 v9fs_file_write(struct file *filp, const char __user * data,
 		size_t count, loff_t * offset)
 {
-	int n, rsize, total = 0;
+	ssize_t retval;
+	size_t total = 0;
+	int n, rsize;
 	struct p9_fid *fid;
 	struct p9_client *clnt;
 	struct inode *inode = filp->f_path.dentry->d_inode;
@@ -234,6 +236,17 @@ v9fs_file_write(struct file *filp, const char __user * data,
 
 	rsize = fid->iounit ? fid->iounit : clnt->msize - P9_IOHDRSZ;
 
+	retval = generic_write_checks(filp, &origin, &count, 0);
+	if (retval)
+		goto out;
+
+	retval = -EINVAL;
+	if ((ssize_t) count < 0)
+		goto out;
+	retval = 0;
+	if (!count)
+		goto out;
+
 	do {
 		if (count < rsize)
 			rsize = count;
@@ -258,9 +271,11 @@ v9fs_file_write(struct file *filp, const char __user * data,
 	}
 
 	if (n < 0)
-		return n;
-
-	return total;
+		retval = n;
+	else
+		retval = total;
+out:
+	return retval;
 }
 
 static int v9fs_file_fsync(struct file *filp, int datasync)