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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.

Fixes: 6460e75a104d ("[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>

authored by

Yang Erkun and committed by
Martin K. Petersen d06a310b 3033c471

+27 -2
+27 -2
drivers/scsi/sg.c
··· 1623 1623 } 1624 1624 1625 1625 module_param_named(scatter_elem_sz, scatter_elem_sz, int, S_IRUGO | S_IWUSR); 1626 - module_param_named(def_reserved_size, def_reserved_size, int, 1627 - S_IRUGO | S_IWUSR); 1628 1626 module_param_named(allow_dio, sg_allow_dio, int, S_IRUGO | S_IWUSR); 1627 + 1628 + static int def_reserved_size_set(const char *val, const struct kernel_param *kp) 1629 + { 1630 + int size, ret; 1631 + 1632 + if (!val) 1633 + return -EINVAL; 1634 + 1635 + ret = kstrtoint(val, 0, &size); 1636 + if (ret) 1637 + return ret; 1638 + 1639 + /* limit to 1 MB */ 1640 + if (size < 0 || size > 1048576) 1641 + return -ERANGE; 1642 + 1643 + def_reserved_size = size; 1644 + return 0; 1645 + } 1646 + 1647 + static const struct kernel_param_ops def_reserved_size_ops = { 1648 + .set = def_reserved_size_set, 1649 + .get = param_get_int, 1650 + }; 1651 + 1652 + module_param_cb(def_reserved_size, &def_reserved_size_ops, &def_reserved_size, 1653 + S_IRUGO | S_IWUSR); 1629 1654 1630 1655 MODULE_AUTHOR("Douglas Gilbert"); 1631 1656 MODULE_DESCRIPTION("SCSI generic (sg) driver");