[PATCH 6.12 087/460] usb: gadget: f_mass_storage: Fix potential integer overflow in check_command_size_in_blocks()

Greg Kroah-Hartman
2026-03-23T14:16:46Z

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

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

From: Seungjin Bae <eeodqql09@gmail.com>

[ Upstream commit 8479891d1f04a8ce55366fe4ca361ccdb96f02e1 ]

The `check_command_size_in_blocks()` function calculates the data size
in bytes by left shifting `common->data_size_from_cmnd` by the block
size (`common->curlun->blkbits`). However, it does not validate whether
this shift operation will cause an integer overflow.

Initially, the block size is set up in `fsg_lun_open()` , and the
`common->data_size_from_cmnd` is set up in `do_scsi_command()`. During
initialization, there is no integer overflow check for the interaction
between two variables.

So if a malicious USB host sends a SCSI READ or WRITE command
requesting a large amount of data (`common->data_size_from_cmnd`), the
left shift operation can wrap around. This results in a truncated data
size, which can bypass boundary checks and potentially lead to memory
corruption or out-of-bounds accesses.

Fix this by using the check_shl_overflow() macro to safely perform the
shift and catch any overflows.

Fixes: 144974e7f9e3 ("usb: gadget: mass_storage: support multi-luns with different logic block size")
Signed-off-by: Seungjin Bae <eeodqql09@gmail.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://patch.msgid.link/20260228104324.1696455-2-eeodqql09@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/usb/gadget/function/f_mass_storage.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
index 08e0d1c511e8d..74cb7e57a197c 100644
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -180,6 +180,7 @@
#include <linux/kthread.h>
#include <linux/sched/signal.h>
#include <linux/limits.h>
+#include <linux/overflow.h>
#include <linux/pagemap.h>
#include <linux/rwsem.h>
#include <linux/slab.h>
@@ -1853,8 +1854,15 @@ static int check_command_size_in_blocks(struct fsg_common *common,
int cmnd_size, enum data_direction data_dir,
unsigned int mask, int needs_medium, const char *name)
{
- if (common->curlun)
- common->data_size_from_cmnd <<= common->curlun->blkbits;
+ if (common->curlun) {
+ if (check_shl_overflow(common->data_size_from_cmnd,
+ common->curlun->blkbits,
+ &common->data_size_from_cmnd)) {
+ common->phase_error = 1;
+ return -EINVAL;
+ }
+ }
+
return check_command(common, cmnd_size, data_dir,
mask, needs_medium, name);
}
--
2.51.0