scsi: sg: Resolve soft lockup issue when opening /dev/sgX

[ Upstream commit d06a310 ]

The parameter def_reserved_size defines the default buffer size reserved
for each Sg_fd and should be restricted to a range between 0 and 1,048,576
(see https://tldp.org/HOWTO/SCSI-Generic-HOWTO/proc.html).  Although the
function sg_proc_write_dressz enforces this limit, it is possible to bypass
it by directly modifying the module parameter as shown below, which then
causes a soft lockup:

echo -1 > /sys/module/sg/parameters/def_reserved_size
exec 4<> /dev/sg0

watchdog: BUG: soft lockup - CPU#5 stuck for 26 seconds! [bash:537]
Modules loaded:
CPU: 5 UID: 0 PID: 537 Command: bash, kernel version 6.19.0-rc3+ #134,
PREEMPT disabled
Hardware: QEMU Standard PC (i440FX + PIIX, 1996), BIOS version
1.16.1-2.fc37 dated 04/01/2014
...
Call Trace:

  sg_build_reserve+0x5c/0xa0
  sg_add_sfp+0x168/0x270
  sg_open+0x16e/0x340
  chrdev_open+0xbe/0x230
  do_dentry_open+0x175/0x480
  vfs_open+0x34/0xf0
  do_open+0x265/0x3d0
  path_openat+0x110/0x290
  do_filp_open+0xc3/0x170
  do_sys_openat2+0x71/0xe0
  __x64_sys_openat+0x6d/0xa0
  do_syscall_64+0x62/0x310
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

The fix is to use module_param_cb to validate and reject invalid values
assigned to def_reserved_size.

Fixes: 6460e75 ("[SCSI] sg: fixes for large page_size")
Signed-off-by: Yang Erkun <yangerkun@huawei.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://patch.msgid.link/20260127062044.3034148-3-yangerkun@huawei.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Yang Erkun

drivers/scsi/sg.c

@@ -1621,10 +1621,35 @@ sg_remove_device(struct device *cl_dev)
 }
 
 module_param_named(scatter_elem_sz, scatter_elem_sz, int, S_IRUGO | S_IWUSR);
-module_param_named(def_reserved_size, def_reserved_size, int,
-		   S_IRUGO | S_IWUSR);
 module_param_named(allow_dio, sg_allow_dio, int, S_IRUGO | S_IWUSR);
 
+static int def_reserved_size_set(const char *val, const struct kernel_param *kp)
+{
+	int size, ret;
+
+	if (!val)
+		return -EINVAL;
+
+	ret = kstrtoint(val, 0, &size);
+	if (ret)
+		return ret;
+
+	/* limit to 1 MB */
+	if (size < 0 || size > 1048576)
+		return -ERANGE;
+
+	def_reserved_size = size;
+	return 0;
+}
+
+static const struct kernel_param_ops def_reserved_size_ops = {
+	.set	= def_reserved_size_set,
+	.get	= param_get_int,
+};
+
+module_param_cb(def_reserved_size, &def_reserved_size_ops, &def_reserved_size,
+		   S_IRUGO | S_IWUSR);
+
 MODULE_AUTHOR("Douglas Gilbert");
 MODULE_DESCRIPTION("SCSI generic (sg) driver");
 MODULE_LICENSE("GPL");