{"vulnerability": "cve-2025-21984", "sightings": [{"uuid": "a00f5bd6-d902-4ab0-9947-9bfcea9bbca3", "vulnerability_lookup_origin": "1a89b78e-f703-45f3-bb86-59eb712668bd", "author": "2a075640-a300-48a4-bb44-bc6130783b9b", "vulnerability": "CVE-2025-21984", "type": "seen", "source": "https://t.me/cvedetector/21785", "content": "{\n  \"Source\": \"CVE FEED\",\n  \"Title\": \"CVE-2025-21984 - Linux Kernel mm Swapcache Vulnerability\", \n  \"Content\": \"CVE ID : CVE-2025-21984 \nPublished : April 1, 2025, 4:15 p.m. | 1\u00a0hour, 15\u00a0minutes ago \nDescription : In the Linux kernel, the following vulnerability has been resolved:  \n  \nmm: fix kernel BUG when userfaultfd_move encounters swapcache  \n  \nuserfaultfd_move() checks whether the PTE entry is present or a  \nswap entry.  \n  \n- If the PTE entry is present, move_present_pte() handles folio  \n  migration by setting:  \n  \n  src_folio->index = linear_page_index(dst_vma, dst_addr);  \n  \n- If the PTE entry is a swap entry, move_swap_pte() simply copies  \n  the PTE to the new dst_addr.  \n  \nThis approach is incorrect because, even if the PTE is a swap entry,  \nit can still reference a folio that remains in the swap cache.  \n  \nThis creates a race window between steps 2 and 4.  \n 1. add_to_swap: The folio is added to the swapcache.  \n 2. try_to_unmap: PTEs are converted to swap entries.  \n 3. pageout: The folio is written back.  \n 4. Swapcache is cleared.  \nIf userfaultfd_move() occurs in the window between steps 2 and 4,  \nafter the swap PTE has been moved to the destination, accessing the  \ndestination triggers do_swap_page(), which may locate the folio in  \nthe swapcache. However, since the folio's index has not been updated  \nto match the destination VMA, do_swap_page() will detect a mismatch.  \n  \nThis can result in two critical issues depending on the system  \nconfiguration.  \n  \nIf KSM is disabled, both small and large folios can trigger a BUG  \nduring the add_rmap operation due to:  \n  \n page_pgoff(folio, page) != linear_page_index(vma, address)  \n  \n[   13.336953] page: refcount:6 mapcount:1 mapping:00000000f43db19c index:0xffffaf150 pfn:0x4667c  \n[   13.337520] head: order:2 mapcount:1 entire_mapcount:0 nr_pages_mapped:1 pincount:0  \n[   13.337716] memcg:ffff00000405f000  \n[   13.337849] anon flags: 0x3fffc0000020459(locked|uptodate|dirty|owner_priv_1|head|swapbacked|node=0|zone=0|lastcpupid=0xffff)  \n[   13.338630] raw: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361  \n[   13.338831] raw: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000  \n[   13.339031] head: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361  \n[   13.339204] head: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000  \n[   13.339375] head: 03fffc0000000202 fffffdffc0199f01 ffffffff00000000 0000000000000001  \n[   13.339546] head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000  \n[   13.339736] page dumped because: VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address))  \n[   13.340190] ------------[ cut here ]------------  \n[   13.340316] kernel BUG at mm/rmap.c:1380!  \n[   13.340683] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP  \n[   13.340969] Modules linked in:  \n[   13.341257] CPU: 1 UID: 0 PID: 107 Comm: a.out Not tainted 6.14.0-rc3-gcf42737e247a-dirty #299  \n[   13.341470] Hardware name: linux,dummy-virt (DT)  \n[   13.341671] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)  \n[   13.341815] pc : __page_check_anon_rmap+0xa0/0xb0  \n[   13.341920] lr : __page_check_anon_rmap+0xa0/0xb0  \n[   13.342018] sp : ffff80008752bb20  \n[   13.342093] x29: ffff80008752bb20 x28: fffffdffc0199f00 x27: 0000000000000001  \n[   13.342404] x26: 0000000000000000 x25: 0000000000000001 x24: 0000000000000001  \n[   13.342575] x23: 0000ffffaf0d0000 x22: 0000ffffaf0d0000 x21: fffffdffc0199f00  \n[   13.342731] x20: fffffdffc0199f00 x19: ffff000006210700 x18: 00000000ffffffff  \n[   13.342881] x17: 6c203d2120296567 x16: 6170202c6f696c6f x15: 662866666f67705f  \n[   13.343033] x14: 6567617028454741 x13: 2929737365726464 x12: ffff800083728ab0  \n[   13.343183] x11: ffff800082996bf8 x10: 0000000000000fd7 x9 : ffff80008011bc40  \n[   13.343351] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000829eebf8  \n[   13.343498] x5 : c0000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000 [...]", "creation_timestamp": "2025-04-01T19:44:30.000000Z"}]}