[PATCH linux-5.4.y 7/8] loop: Check for overflow while configuring loop

[Genjian]

From: Siddh Raman Pant <code@xxxxxxxx>

[ Upstream commit c490a0b5a4f36da3918181a8acdc6991d967c5f3 ]

The userspace can configure a loop using an ioctl call, wherein
a configuration of type loop_config is passed (see lo_ioctl()'s
case on line 1550 of drivers/block/loop.c). This proceeds to call
loop_configure() which in turn calls loop_set_status_from_info()
(see line 1050 of loop.c), passing &config->info which is of type
loop_info64*. This function then sets the appropriate values, like
the offset.

loop_device has lo_offset of type loff_t (see line 52 of loop.c),
which is typdef-chained to long long, whereas loop_info64 has
lo_offset of type __u64 (see line 56 of include/uapi/linux/loop.h).

The function directly copies offset from info to the device as
follows (See line 980 of loop.c):
	lo->lo_offset = info->lo_offset;

This results in an overflow, which triggers a warning in iomap_iter()
due to a call to iomap_iter_done() which has:
	WARN_ON_ONCE(iter->iomap.offset > iter->pos);

Thus, check for negative value during loop_set_status_from_info().

Bug report: https://syzkaller.appspot.com/bug?id=c620fe14aac810396d3c3edc9ad73848bf69a29e

Reported-and-tested-by: syzbot+a8e049cd3abd342936b6@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Siddh Raman Pant <code@xxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Link: https://lore.kernel.org/r/20220823160810.181275-1-code@xxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Genjian Zhang <zhanggenjian@xxxxxxxxxx>
---
 drivers/block/loop.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index eadb189be0cc..c999eef4e345 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1298,6 +1298,11 @@ loop_set_status_from_info(struct loop_device *lo,
 
 	lo->lo_offset = info->lo_offset;
 	lo->lo_sizelimit = info->lo_sizelimit;
+
+	/* loff_t vars have been assigned __u64 */
+	if (lo->lo_offset < 0 || lo->lo_sizelimit < 0)
+		return -EOVERFLOW;
+
 	memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
 	memcpy(lo->lo_crypt_name, info->lo_crypt_name, LO_NAME_SIZE);
 	lo->lo_file_name[LO_NAME_SIZE-1] = 0;
-- 
2.25.1