[PATCH 4.19 74/77] Revert "loop: Remove sector_t truncation checks"

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@decadent.org.uk>

This reverts commit f92a3b0d003b9f7eb1f452598966a08802183f47, which
was commit 083a6a50783ef54256eec3499e6575237e0e3d53 upstream.  In 4.19
there is still an option to use 32-bit sector_t on 32-bit
architectures, so we need to keep checking for truncation.

Since loop_set_status() was refactored by subsequent patches, this
reintroduces its truncation check in loop_set_status_from_info()
instead.

I tested that the loop ioctl operations have the expected behaviour on
x86_64, x86_32 with CONFIG_LBDAF=y, and (the special case) x86_32 with
CONFIG_LBDAF=n.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/block/loop.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -243,12 +243,16 @@ static void loop_set_size(struct loop_de
 	kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
 }
 
-static void
+static int
 figure_loop_size(struct loop_device *lo, loff_t offset, loff_t sizelimit)
 {
 	loff_t size = get_size(offset, sizelimit, lo->lo_backing_file);
+	sector_t x = (sector_t)size;
 
+	if (unlikely((loff_t)x != size))
+		return -EFBIG;
 	loop_set_size(lo, size);
+	return 0;
 }
 
 static inline int
@@ -996,7 +1000,10 @@ static int loop_set_fd(struct loop_devic
 	    !file->f_op->write_iter)
 		lo_flags |= LO_FLAGS_READ_ONLY;
 
+	error = -EFBIG;
 	size = get_loop_size(lo, file);
+	if ((loff_t)(sector_t)size != size)
+		goto out_unlock;
 
 	error = loop_prepare_queue(lo);
 	if (error)
@@ -1246,6 +1253,7 @@ loop_set_status_from_info(struct loop_de
 	int err;
 	struct loop_func_table *xfer;
 	kuid_t uid = current_uid();
+	loff_t new_size;
 
 	if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE)
 		return -EINVAL;
@@ -1273,6 +1281,11 @@ loop_set_status_from_info(struct loop_de
 	if (info->lo_offset > LLONG_MAX || info->lo_sizelimit > LLONG_MAX)
 		return -EOVERFLOW;
 
+	new_size = get_size(info->lo_offset, info->lo_sizelimit,
+			    lo->lo_backing_file);
+	if ((loff_t)(sector_t)new_size != new_size)
+		return -EFBIG;
+
 	lo->lo_offset = info->lo_offset;
 	lo->lo_sizelimit = info->lo_sizelimit;
 
@@ -1531,9 +1544,7 @@ static int loop_set_capacity(struct loop
 	if (unlikely(lo->lo_state != Lo_bound))
 		return -ENXIO;
 
-	figure_loop_size(lo, lo->lo_offset, lo->lo_sizelimit);
-
-	return 0;
+	return figure_loop_size(lo, lo->lo_offset, lo->lo_sizelimit);
 }
 
 static int loop_set_dio(struct loop_device *lo, unsigned long arg)