{"cve":"CVE-2022-49760","nvd":{"published":"2025-03-27T17:15:41.280","modified":"2026-10-15T22:17:25.033","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/hugetlb: fix PTE marker handling in hugetlb_change_protection()\n\nPatch series \"mm/hugetlb: uffd-wp fixes for hugetlb_change_protection()\".\n\nPlaying with virtio-mem and background snapshots (using uffd-wp) on\nhugetlb in QEMU, I managed to trigger a VM_BUG_ON().  Looking into the\ndetails, hugetlb_change_protection() seems to not handle uffd-wp correctly\nin all cases.\n\nPatch #1 fixes my test case.  I don't have reproducers for patch #2, as it\nrequires running into migration entries.\n\nI did not yet check in detail yet if !hugetlb code requires similar care.\n\n\nThis patch (of 2):\n\nThere are two problematic cases when stumbling over a PTE marker in\nhugetlb_change_protection():\n\n(1) We protect an uffd-wp PTE marker a second time using uffd-wp: we will\n    end up in the \"!huge_pte_none(pte)\" case and mess up the PTE marker.\n\n(2) We unprotect a uffd-wp PTE marker: we will similarly end up in the\n    \"!huge_pte_none(pte)\" case even though we cleared the PTE, because\n    the \"pte\" variable is stale. We'll mess up the PTE marker.\n\nFor example, if we later stumble over such a \"wrongly modified\" PTE marker,\nwe'll treat it like a present PTE that maps some garbage page.\n\nThis can, for example, be triggered by mapping a memfd backed by huge\npages, registering uffd-wp, uffd-wp'ing an unmapped page and (a)\nuffd-wp'ing it a second time; or (b) uffd-unprotecting it; or (c)\nunregistering uffd-wp. Then, ff we trigger fallocate(FALLOC_FL_PUNCH_HOLE)\non that file range, we will run into a VM_BUG_ON:\n\n[  195.039560] page:00000000ba1f2987 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x0\n[  195.039565] flags: 0x7ffffc0001000(reserved|node=0|zone=0|lastcpupid=0x1fffff)\n[  195.039568] raw: 0007ffffc0001000 ffffe742c0000008 ffffe742c0000008 0000000000000000\n[  195.039569] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000\n[  195.039569] page dumped because: VM_BUG_ON_PAGE(compound && !PageHead(page))\n[  195.039573] ------------[ cut here ]------------\n[  195.039574] kernel BUG at mm/rmap.c:1346!\n[  195.039579] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI\n[  195.039581] CPU: 7 PID: 4777 Comm: qemu-system-x86 Not tainted 6.0.12-200.fc36.x86_64 #1\n[  195.039583] Hardware name: LENOVO 20WNS1F81N/20WNS1F81N, BIOS N35ET50W (1.50 ) 09/15/2022\n[  195.039584] RIP: 0010:page_remove_rmap+0x45b/0x550\n[  195.039588] Code: [...]\n[  195.039589] RSP: 0018:ffffbc03c3633ba8 EFLAGS: 00010292\n[  195.039591] RAX: 0000000000000040 RBX: ffffe742c0000000 RCX: 0000000000000000\n[  195.039592] RDX: 0000000000000002 RSI: ffffffff8e7aac1a RDI: 00000000ffffffff\n[  195.039592] RBP: 0000000000000001 R08: 0000000000000000 R09: ffffbc03c3633a08\n[  195.039593] R10: 0000000000000003 R11: ffffffff8f146328 R12: ffff9b04c42754b0\n[  195.039594] R13: ffffffff8fcc6328 R14: ffffbc03c3633c80 R15: ffff9b0484ab9100\n[  195.039595] FS:  00007fc7aaf68640(0000) GS:ffff9b0bbf7c0000(0000) knlGS:0000000000000000\n[  195.039596] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n[  195.039597] CR2: 000055d402c49110 CR3: 0000000159392003 CR4: 0000000000772ee0\n[  195.039598] PKRU: 55555554\n[  195.039599] Call Trace:\n[  195.039600]  <TASK>\n[  195.039602]  __unmap_hugepage_range+0x33b/0x7d0\n[  195.039605]  unmap_hugepage_range+0x55/0x70\n[  195.039608]  hugetlb_vmdelete_list+0x77/0xa0\n[  195.039611]  hugetlbfs_fallocate+0x410/0x550\n[  195.039612]  ? _raw_spin_unlock_irqrestore+0x23/0x40\n[  195.039616]  vfs_fallocate+0x12e/0x360\n[  195.039618]  __x64_sys_fallocate+0x40/0x70\n[  195.039620]  do_syscall_64+0x58/0x80\n[  195.039623]  ? syscall_exit_to_user_mode+0x17/0x40\n[  195.039624]  ? do_syscall_64+0x67/0x80\n[  195.039626]  entry_SYSCALL_64_after_hwframe+0x63/0xcd\n[  195.039628] RIP: 0033:0x7fc7b590651f\n[  195.039653] Code: [...]\n[  195.039654] RSP: 002b:00007fc7aaf66e70 EFLAGS: 00000293 ORIG_RAX: 000000000000011d\n[  195.039655] RAX: ffffffffffffffda RBX: 0000558ef4b7f370 RCX: 00007fc7b590651f\n---truncated---","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/0e678153f5be7e6c8d28835f5a678618da4b7a9c","https://git.kernel.org/stable/c/6062c992e912df1eedad52cf64efb3d48e8d35c5"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:00:28.034033815+00:00"},"epss":{"cve":"CVE-2022-49760","score":0.00173,"percentile":0.06601,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}