In the Linux kernel, the following vulnerability has been resolved:
blk-cgroup: Fix UAF in blkcgunpinonline()
blkcgunpinonline() walks up the blkcg hierarchy putting the online pin. To walk up, it uses blkcgparent(blkcg) but it was calling that after blkcgdestroy_blkgs(blkcg) which could free the blkcg, leading to the following UAF:
================================================================== BUG: KASAN: slab-use-after-free in blkcgunpinonline+0x15a/0x270 Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117
CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022 Workqueue: cgwbrelease cgwbreleaseworkfn Call Trace: <TASK> dumpstacklvl+0x27/0x80 printreport+0x151/0x710 kasanreport+0xc0/0x100 blkcgunpinonline+0x15a/0x270 cgwbreleaseworkfn+0x194/0x480 processscheduledworks+0x71b/0xe20 workerthread+0x82a/0xbd0 kthread+0x242/0x2c0 retfromfork+0x33/0x70 retfromforkasm+0x1a/0x30 </TASK> ... Freed by task 1944: kasansavetrack+0x2b/0x70 kasansavefreeinfo+0x3c/0x50 _kasanslabfree+0x33/0x50 kfree+0x10c/0x330 cssfreerworkfn+0xe6/0xb30 processscheduledworks+0x71b/0xe20 workerthread+0x82a/0xbd0 kthread+0x242/0x2c0 retfromfork+0x33/0x70 retfromforkasm+0x1a/0x30
Note that the UAF is not easy to trigger as the free path is indirected behind a couple RCU grace periods and a work item execution. I could only trigger it with artifical msleep() injected in blkcgunpinonline().
Fix it by reading the parent pointer before destroying the blkcg's blkg's.
[
{
"id": "CVE-2024-56672-14cf1b3e",
"target": {
"file": "block/blk-cgroup.c",
"function": "blkcg_unpin_online"
},
"digest": {
"function_hash": "156976126850392330542686463781899570777",
"length": 188.0
},
"deprecated": false,
"signature_type": "Function",
"source": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git@29d1e06560f0f6179062ac638b4064deb637d1ad",
"signature_version": "v1"
},
{
"id": "CVE-2024-56672-3449698a",
"target": {
"file": "include/linux/blk-cgroup.h"
},
"digest": {
"threshold": 0.9,
"line_hashes": [
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},
"deprecated": false,
"signature_type": "Line",
"source": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git@83f5a87ee8caa76a917f59912a74d6811f773c67",
"signature_version": "v1"
},
{
"id": "CVE-2024-56672-71be183d",
"target": {
"file": "include/linux/blk-cgroup.h",
"function": "blkcg_unpin_online"
},
"digest": {
"function_hash": "214354245119896662047932459037259942393",
"length": 177.0
},
"deprecated": false,
"signature_type": "Function",
"source": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git@8a07350fe070017a887433f4d6909433955be5f1",
"signature_version": "v1"
},
{
"id": "CVE-2024-56672-8e72100c",
"target": {
"file": "block/blk-cgroup.c"
},
"digest": {
"threshold": 0.9,
"line_hashes": [
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]
},
"deprecated": false,
"signature_type": "Line",
"source": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git@29d1e06560f0f6179062ac638b4064deb637d1ad",
"signature_version": "v1"
},
{
"id": "CVE-2024-56672-9c6e93fd",
"target": {
"file": "include/linux/blk-cgroup.h",
"function": "blkcg_unpin_online"
},
"digest": {
"function_hash": "214354245119896662047932459037259942393",
"length": 177.0
},
"deprecated": false,
"signature_type": "Function",
"source": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git@83f5a87ee8caa76a917f59912a74d6811f773c67",
"signature_version": "v1"
},
{
"id": "CVE-2024-56672-b2b5450c",
"target": {
"file": "include/linux/blk-cgroup.h"
},
"digest": {
"threshold": 0.9,
"line_hashes": [
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]
},
"deprecated": false,
"signature_type": "Line",
"source": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git@8a07350fe070017a887433f4d6909433955be5f1",
"signature_version": "v1"
}
]