问题：
el0_svc_handler+0x190/0x260 arch/arm64/kernel/syscall.c:190
el0_svc+0x10/0x218 arch/arm64/kernel/entry.S:1017
kobject_add_internal failed for 43:0 with -EEXIST, don't try to register things with the same name in the same directory.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 239 at block/genhd.c:724 __device_add_disk+0xb98/0xdf8 block/genhd.c:724
Modules linked in:

问题分析：
nbd_genl_connect
（获取index）
nbd_dev_add（传入巨大负数index，check的时候进行左移比较，仍可正常创建，index值可能与已有的index重复）；

int first_minor = index << part_shift;

/*
 * Too big index can cause duplicate creation of sysfs files/links,
 * because MKDEV() expect that the max first minor is MINORMASK, or
 * index << part_shift can overflow.
 */
if (first_minor < index || first_minor > MINORMASK)
	return -EINVAL;

    当巨大的负值左移时，有可能将其左移成正数，可能与原index重复，导致异常

问题复现：
构造问题场景：
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index a35189098581..3773bcf83993 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1702,8 +1702,14 @@ static int nbd_dev_add(int index)
struct gendisk *disk;
struct request_queue *q;
int err = -ENOMEM;

•   int first_minor = index << part_shift;
  

•   printk("%s index %d %d\n", __func__, index,  MINORMASK);
  

•   if (index == 1) {
  

•           index = -2147483648;
  

•   }
  

•   int first_minor = index << part_shift;
  

•   printk("first_minor %d\n", first_minor);
    /*
     * Too big index can cause duplicate creation of sysfs files/links,
     * because MKDEV() expect that the max first minor is MINORMASK, or
  

@@ -1854,6 +1860,7 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
printk(KERN_ERR "nbd: must specify a size in bytes for the device\n");
return -EINVAL;
}
+

复现结果如下：

localhost login: [ 28.306327] nbd_dev_add index 0 1048575
[ 28.307030] first_minor 0
[ 28.309128] nbd_dev_add index 1 1048575
[ 28.309812] first_minor 0
[ 28.310589] sysfs: cannot create duplicate filename '/devices/virtual/bdi/43:0'
[ 28.311837] CPU: 25 PID: 1166 Comm: modprobe Not tainted 4.19.90-dirty #145
[ 28.313010] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
[ 28.315252] Call Trace:
[ 28.315699] dump_stack+0xd4/0x10f
[ 28.316284] sysfs_warn_dup.cold+0x27/0x45
[ 28.316982] sysfs_create_dir_ns+0xec/0x110
[ 28.317682] kobject_add_internal+0x127/0x520
[ 28.318422] kobject_add_varg+0x39/0x50
[ 28.319073] kobject_add+0x60/0x90
[ 28.319649] ? mutex_lock+0x16/0x60
[ 28.320240] ? get_device_parent.isra.0+0x106/0x310
[ 28.321070] device_add+0x1ae/0xb10
[ 28.321665] bdi_register_va+0x10b/0x430
[ 28.322329] bdi_register+0x5b/0x80
[ 28.322923] ? vsnprintf+0x440/0x7d0
[ 28.323520] bdi_register_owner+0x34/0x80
[ 28.324197] __device_add_disk+0x52b/0x6a0
[ 28.324900] device_add_disk+0x17/0x20
[ 28.325533] nbd_dev_add+0x370/0x3cf [nbd]
[ 28.326225] ? 0xffffffffc0368000
[ 28.326783] nbd_init+0x18a/0x1000 [nbd]
[ 28.327442] do_one_initcall+0x7b/0x33f
[ 28.328088] ? gcov_event+0x70/0x676
[ 28.328690] do_init_module+0xa6/0x340
[ 28.329328] load_module+0x2132/0x24d0
[ 28.329969] ? __do_sys_finit_module+0x13a/0x190
[ 28.330732] __do_sys_finit_module+0x13a/0x190
[ 28.331481] __x64_sys_finit_module+0x1e/0x30
[ 28.332215] do_syscall_64+0xc1/0x250
[ 28.332838] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 28.333682] RIP: 0033:0x7f2fdedbc4e9
[ 28.334279] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 6f 39 2c 00 f7 d8 64 89 01 48
[ 28.337318] RSP: 002b:00007fff2a5cac68 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 28.338576] RAX: ffffffffffffffda RBX: 00005563cf1473d0 RCX: 00007f2fdedbc4e9
[ 28.339759] RDX: 0000000000000000 RSI: 00005563cee1bc26 RDI: 0000000000000003
[ 28.340932] RBP: 00005563cee1bc26 R08: 0000000000000000 R09: 0000000000000000
[ 28.342099] R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
[ 28.343171] R13: 00005563cf147360 R14: 0000000000040000 R15: 00005563cf1473d0
[ 28.344130] kobject_add_internal failed for 43:0 with -EEXIST, don't try to register things with the same name in the same directory.
[ 28.345695] ------------[ cut here ]------------
[ 28.346334] WARNING: CPU: 25 PID: 1166 at block/genhd.c:725 __device_add_disk.cold+0x40/0x150
[ 28.347444] Modules linked in: nbd(+)
[ 28.347941] CPU: 25 PID: 1166 Comm: modprobe Not tainted 4.19.90-dirty #145
[ 28.348851] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
[ 28.350579] RIP: 0010:__device_add_disk.cold+0x40/0x150
[ 28.351268] Code: ff 48 83 05 76 7b 8e 04 01 e9 95 ea ff ff 48 c7 c7 90 2c be 9e 48 83 05 6a 6c 8e 04 01 e8 13 b2 7a ff 48 83 05 65 6c 8e 04 01 <0f> 0b 48 83 05 63 6c 8e 04 01 48 83 05 63 6c 8e 04 01 e9 29 ed ff
[ 28.353701] RSP: 0018:ffffc900084e7c28 EFLAGS: 00010202
[ 28.354388] RAX: 0000000000000024 RBX: 0000000000000000 RCX: 0000000000000000
[ 28.355323] RDX: 0000000000000000 RSI: ffff88900f255bf8 RDI: ffff88900f255bf8
[ 28.356253] RBP: ffff88810845c000 R08: ffff88900f255bf8 R09: 0000000000000005
[ 28.357186] R10: 00000000000003df R11: ffffffff9feb6f4d R12: 0000000000000001
[ 28.358117] R13: ffff88810845c00c R14: 0000000000000000 R15: ffff88810845c070
[ 28.359050] FS: 00007f2fdf8e9040(0000) GS:ffff88900f240000(0000) knlGS:0000000000000000
[ 28.360103] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 28.360857] CR2: 00007f2fdee32395 CR3: 0000000123954000 CR4: 00000000000006e0
[ 28.361796] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 28.362721] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 28.363648] Call Trace:
[ 28.363978] device_add_disk+0x17/0x20
[ 28.364472] nbd_dev_add+0x370/0x3cf [nbd]
[ 28.365014] ? 0xffffffffc0368000
[ 28.365450] nbd_init+0x18a/0x1000 [nbd]
[ 28.365975] do_one_initcall+0x7b/0x33f
[ 28.366475] ? gcov_event+0x70/0x676
[ 28.366954] do_init_module+0xa6/0x340
[ 28.367443] load_module+0x2132/0x24d0
[ 28.367944] ? __do_sys_finit_module+0x13a/0x190
[ 28.368542] __do_sys_finit_module+0x13a/0x190
[ 28.369123] __x64_sys_finit_module+0x1e/0x30
[ 28.369694] do_syscall_64+0xc1/0x250
[ 28.370178] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 28.370838] RIP: 0033:0x7f2fdedbc4e9
[ 28.371307] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 6f 39 2c 00 f7 d8 64 89 01 48
[ 28.373705] RSP: 002b:00007fff2a5cac68 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 28.374680] RAX: ffffffffffffffda RBX: 00005563cf1473d0 RCX: 00007f2fdedbc4e9
[ 28.375593] RDX: 0000000000000000 RSI: 00005563cee1bc26 RDI: 0000000000000003
[ 28.376493] RBP: 00005563cee1bc26 R08: 0000000000000000 R09: 0000000000000000
[ 28.377395] R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
[ 28.378297] R13: 00005563cf147360 R14: 0000000000040000 R15: 00005563cf1473d0
[ 28.379202] ---[ end trace c19b64e7262f65ca ]---
[ 28.379837] sysfs: cannot create duplicate filename '/dev/block/43:0'
[ 28.380673] CPU: 25 PID: 1166 Comm: modprobe Tainted: G W 4.19.90-dirty #145
[ 28.381744] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
[ 28.383421] Call Trace:
[ 28.383750] dump_stack+0xd4/0x10f
[ 28.384193] sysfs_warn_dup.cold+0x27/0x45
[ 28.384722] sysfs_do_create_link_sd.isra.0+0x107/0x120
[ 28.385400] sysfs_create_link+0x29/0x60
[ 28.385910] device_add+0xa87/0xb10
[ 28.386362] __device_add_disk+0x1fe/0x6a0
[ 28.386895] device_add_disk+0x17/0x20
[ 28.387381] nbd_dev_add+0x370/0x3cf [nbd]
[ 28.387918] ? 0xffffffffc0368000
[ 28.388350] nbd_init+0x18a/0x1000 [nbd]
[ 28.388860] do_one_initcall+0x7b/0x33f
[ 28.389353] ? gcov_event+0x70/0x676
[ 28.389821] do_init_module+0xa6/0x340
[ 28.390309] load_module+0x2132/0x24d0
[ 28.390798] ? __do_sys_finit_module+0x13a/0x190
[ 28.391394] __do_sys_finit_module+0x13a/0x190
[ 28.391969] __x64_sys_finit_module+0x1e/0x30
[ 28.392529] do_syscall_64+0xc1/0x250
[ 28.393015] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 28.393660] RIP: 0033:0x7f2fdedbc4e9
[ 28.394122] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 6f 39 2c 00 f7 d8 64 89 01 48
[ 28.396488] RSP: 002b:00007fff2a5cac68 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[ 28.397451] RAX: ffffffffffffffda RBX: 00005563cf1473d0 RCX: 00007f2fdedbc4e9
[ 28.398366] RDX: 0000000000000000 RSI: 00005563cee1bc26 RDI: 0000000000000003
[ 28.399277] RBP: 00005563cee1bc26 R08: 0000000000000000 R09: 0000000000000000
[ 28.400193] R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
[ 28.401107] R13: 00005563cf147360 R14: 0000000000040000 R15: 00005563cf1473d0
[ 28.402056] ------------[ cut here ]------------
[ 28.402662] WARNING: CPU: 25 PID: 1166 at fs/sysfs/group.c:115 internal_create_group+0x348/0x660
[ 28.403796] Modules linked in: nbd(+)
[ 28.404277] CPU: 25 PID: 1166 Comm: modprobe Tainted: G W 4.19.90-dirty #145
[ 28.405353] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
[ 28.407056] RIP: 0010:internal_create_group+0x348/0x660
[ 28.407731] Code: 04 01 89 e8 eb 8f 48 83 05 b4 f9 c0 04 01 48 c7 c7 90 2c be 9e 48 83 05 c5 f9