vfs: in iomap seek_{hole,data}, return -ENXIO for negative offsets

In the iomap implementations of SEEK_HOLE and SEEK_DATA, make sure we
return -ENXIO for negative offsets.
Inspired-by: Mateusz S <muttdini@gmail.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/iomap.c

@@ -610,8 +610,8 @@ iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
 	loff_t length = size - offset;
 	loff_t ret;
 
-	/* Nothing to be found beyond the end of the file. */
-	if (offset >= size)
+	/* Nothing to be found before or beyond the end of the file. */
+	if (offset < 0 || offset >= size)
 		return -ENXIO;
 
 	while (length > 0) {
@@ -656,8 +656,8 @@ iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
 	loff_t length = size - offset;
 	loff_t ret;
 
-	/* Nothing to be found beyond the end of the file. */
-	if (offset >= size)
+	/* Nothing to be found before or beyond the end of the file. */
+	if (offset < 0 || offset >= size)
 		return -ENXIO;
 
 	while (length > 0) {