GHSA-MH6M-GJCW-57PH
Vulnerability from github – Published: 2024-12-28 12:30 – Updated: 2025-11-03 21:32In the Linux kernel, the following vulnerability has been resolved:
brd: defer automatic disk creation until module initialization succeeds
My colleague Wupeng found the following problems during fault injection:
BUG: unable to handle page fault for address: fffffbfff809d073 PGD 6e648067 P4D 123ec8067 PUD 123ec4067 PMD 100e38067 PTE 0 Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI CPU: 5 UID: 0 PID: 755 Comm: modprobe Not tainted 6.12.0-rc3+ #17 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:__asan_load8+0x4c/0xa0 ... Call Trace: blkdev_put_whole+0x41/0x70 bdev_release+0x1a3/0x250 blkdev_release+0x11/0x20 __fput+0x1d7/0x4a0 task_work_run+0xfc/0x180 syscall_exit_to_user_mode+0x1de/0x1f0 do_syscall_64+0x6b/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e
loop_init() is calling loop_add() after __register_blkdev() succeeds and is ignoring disk_add() failure from loop_add(), for loop_add() failure is not fatal and successfully created disks are already visible to bdev_open().
brd_init() is currently calling brd_alloc() before __register_blkdev() succeeds and is releasing successfully created disks when brd_init() returns an error. This can cause UAF for the latter two case:
case 1: T1: modprobe brd brd_init brd_alloc(0) // success add_disk disk_scan_partitions bdev_file_open_by_dev // alloc file fput // won't free until back to userspace brd_alloc(1) // failed since mem alloc error inject // error path for modprobe will release code segment // back to userspace __fput blkdev_release bdev_release blkdev_put_whole bdev->bd_disk->fops->release // fops is freed now, UAF!
case 2: T1: T2: modprobe brd brd_init brd_alloc(0) // success open(/dev/ram0) brd_alloc(1) // fail // error path for modprobe
close(/dev/ram0)
...
/* UAF! */
bdev->bd_disk->fops->release
Fix this problem by following what loop_init() does. Besides, reintroduce brd_devices_mutex to help serialize modifications to brd_list.
{
"affected": [],
"aliases": [
"CVE-2024-56693"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-12-28T10:15:14Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbrd: defer automatic disk creation until module initialization succeeds\n\nMy colleague Wupeng found the following problems during fault injection:\n\nBUG: unable to handle page fault for address: fffffbfff809d073\nPGD 6e648067 P4D 123ec8067 PUD 123ec4067 PMD 100e38067 PTE 0\nOops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI\nCPU: 5 UID: 0 PID: 755 Comm: modprobe Not tainted 6.12.0-rc3+ #17\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS\n1.16.1-2.fc37 04/01/2014\nRIP: 0010:__asan_load8+0x4c/0xa0\n...\nCall Trace:\n \u003cTASK\u003e\n blkdev_put_whole+0x41/0x70\n bdev_release+0x1a3/0x250\n blkdev_release+0x11/0x20\n __fput+0x1d7/0x4a0\n task_work_run+0xfc/0x180\n syscall_exit_to_user_mode+0x1de/0x1f0\n do_syscall_64+0x6b/0x170\n entry_SYSCALL_64_after_hwframe+0x76/0x7e\n\nloop_init() is calling loop_add() after __register_blkdev() succeeds and\nis ignoring disk_add() failure from loop_add(), for loop_add() failure\nis not fatal and successfully created disks are already visible to\nbdev_open().\n\nbrd_init() is currently calling brd_alloc() before __register_blkdev()\nsucceeds and is releasing successfully created disks when brd_init()\nreturns an error. This can cause UAF for the latter two case:\n\ncase 1:\n T1:\nmodprobe brd\n brd_init\n brd_alloc(0) // success\n add_disk\n disk_scan_partitions\n bdev_file_open_by_dev // alloc file\n fput // won\u0027t free until back to userspace\n brd_alloc(1) // failed since mem alloc error inject\n // error path for modprobe will release code segment\n // back to userspace\n __fput\n blkdev_release\n bdev_release\n blkdev_put_whole\n bdev-\u003ebd_disk-\u003efops-\u003erelease // fops is freed now, UAF!\n\ncase 2:\n T1: T2:\nmodprobe brd\n brd_init\n brd_alloc(0) // success\n open(/dev/ram0)\n brd_alloc(1) // fail\n // error path for modprobe\n\n close(/dev/ram0)\n ...\n /* UAF! */\n bdev-\u003ebd_disk-\u003efops-\u003erelease\n\nFix this problem by following what loop_init() does. Besides,\nreintroduce brd_devices_mutex to help serialize modifications to\nbrd_list.",
"id": "GHSA-mh6m-gjcw-57ph",
"modified": "2025-11-03T21:32:01Z",
"published": "2024-12-28T12:30:47Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-56693"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/259bf925583ec9e3781df778cadf00594095090d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/410896624db639500f24f46478b4bfa05c76bf56"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/41219c147df8bbd6591f59af5d695fb6c9a1cbff"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/63dfd728b30f79495dacc886127695a379805152"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/826cc42adf44930a633d11a5993676d85ddb0842"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c0c2744cd2939ec5999c51dbaf2af16886548b7b"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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