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

In the Linux kernel, the following vulnerability has been resolved:

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

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.