usb: gadget: f_mass_storage: Fix potential integer overflow in check_command_size_in_blocks()

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: 144974e ("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>

Author: pip-izony

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);
 }