ghsa-w9mj-34hr-82rj
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
btrfs: do not ASSERT() if the newly created subvolume already got read
[BUG] There is a syzbot crash, triggered by the ASSERT() during subvolume creation:
assertion failed: !anon_dev, in fs/btrfs/disk-io.c:1319
------------[ cut here ]------------
kernel BUG at fs/btrfs/disk-io.c:1319!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:btrfs_get_root_ref.part.0+0x9aa/0xa60
[CAUSE] During create_subvol(), after inserting root item for the newly created subvolume, we would trigger btrfs_get_new_fs_root() to get the btrfs_root of that subvolume.
The idea here is, we have preallocated an anonymous device number for the subvolume, thus we can assign it to the new subvolume.
But there is really nothing preventing things like backref walk to read the new subvolume. If that happens before we call btrfs_get_new_fs_root(), the subvolume would be read out, with a new anonymous device number assigned already.
In that case, we would trigger ASSERT(), as we really expect no one to read out that subvolume (which is not yet accessible from the fs). But things like backref walk is still possible to trigger the read on the subvolume.
Thus our assumption on the ASSERT() is not correct in the first place.
[FIX] Fix it by removing the ASSERT(), and just free the @anon_dev, reset it to 0, and continue.
If the subvolume tree is read out by something else, it should have already get a new anon_dev assigned thus we only need to free the preallocated one.
{
"affected": [],
"aliases": [
"CVE-2024-26727"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-04-03T15:15:54Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: do not ASSERT() if the newly created subvolume already got read\n\n[BUG]\nThere is a syzbot crash, triggered by the ASSERT() during subvolume\ncreation:\n\n assertion failed: !anon_dev, in fs/btrfs/disk-io.c:1319\n ------------[ cut here ]------------\n kernel BUG at fs/btrfs/disk-io.c:1319!\n invalid opcode: 0000 [#1] PREEMPT SMP KASAN\n RIP: 0010:btrfs_get_root_ref.part.0+0x9aa/0xa60\n \u003cTASK\u003e\n btrfs_get_new_fs_root+0xd3/0xf0\n create_subvol+0xd02/0x1650\n btrfs_mksubvol+0xe95/0x12b0\n __btrfs_ioctl_snap_create+0x2f9/0x4f0\n btrfs_ioctl_snap_create+0x16b/0x200\n btrfs_ioctl+0x35f0/0x5cf0\n __x64_sys_ioctl+0x19d/0x210\n do_syscall_64+0x3f/0xe0\n entry_SYSCALL_64_after_hwframe+0x63/0x6b\n ---[ end trace 0000000000000000 ]---\n\n[CAUSE]\nDuring create_subvol(), after inserting root item for the newly created\nsubvolume, we would trigger btrfs_get_new_fs_root() to get the\nbtrfs_root of that subvolume.\n\nThe idea here is, we have preallocated an anonymous device number for\nthe subvolume, thus we can assign it to the new subvolume.\n\nBut there is really nothing preventing things like backref walk to read\nthe new subvolume.\nIf that happens before we call btrfs_get_new_fs_root(), the subvolume\nwould be read out, with a new anonymous device number assigned already.\n\nIn that case, we would trigger ASSERT(), as we really expect no one to\nread out that subvolume (which is not yet accessible from the fs).\nBut things like backref walk is still possible to trigger the read on\nthe subvolume.\n\nThus our assumption on the ASSERT() is not correct in the first place.\n\n[FIX]\nFix it by removing the ASSERT(), and just free the @anon_dev, reset it\nto 0, and continue.\n\nIf the subvolume tree is read out by something else, it should have\nalready get a new anon_dev assigned thus we only need to free the\npreallocated one.",
"id": "GHSA-w9mj-34hr-82rj",
"modified": "2024-06-25T21:31:12Z",
"published": "2024-04-03T15:30:44Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-26727"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3f5d47eb163bceb1b9e613c9003bae5fefc0046f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5a172344bfdabb46458e03708735d7b1a918c468"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/66b317a2fc45b2ef66527ee3f8fa08fb5beab88d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/833775656d447c545133a744a0ed1e189ce61430"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e03ee2fe873eb68c1f9ba5112fee70303ebf9dfb"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e31546b0f34af21738c4ceac47d662c00ee6382f"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html"
}
],
"schema_version": "1.4.0",
"severity": []
}
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