{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-38554", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-04-16T04:51:24.025Z", "datePublished": "2025-08-19T17:02:33.315Z", "dateUpdated": "2026-08-05T12:02:52.067Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:02:52.067Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: fix a UAF when vma->mm is freed after vma->vm_refcnt got dropped\n\nBy inducing delays in the right places, Jann Horn created a reproducer for\na hard to hit UAF issue that became possible after VMAs were allowed to be\nrecycled by adding SLAB_TYPESAFE_BY_RCU to their cache.\n\nRace description is borrowed from Jann's discovery report:\nlock_vma_under_rcu() looks up a VMA locklessly with mas_walk() under\nrcu_read_lock(). At that point, the VMA may be concurrently freed, and it\ncan be recycled by another process. vma_start_read() then increments the\nvma->vm_refcnt (if it is in an acceptable range), and if this succeeds,\nvma_start_read() can return a recycled VMA.\n\nIn this scenario where the VMA has been recycled, lock_vma_under_rcu()\nwill then detect the mismatching ->vm_mm pointer and drop the VMA through\nvma_end_read(), which calls vma_refcount_put(). vma_refcount_put() drops\nthe refcount and then calls rcuwait_wake_up() using a copy of vma->vm_mm. \nThis is wrong: It implicitly assumes that the caller is keeping the VMA's\nmm alive, but in this scenario the caller has no relation to the VMA's mm,\nso the rcuwait_wake_up() can cause UAF.\n\nThe diagram depicting the race:\nT1 T2 T3\n== == ==\nlock_vma_under_rcu\n mas_walk\n \n mmap\n \n vma_start_read\n __refcount_inc_not_zero_limited_acquire\n munmap\n __vma_enter_locked\n refcount_add_not_zero\n vma_end_read\n vma_refcount_put\n __refcount_dec_and_test\n rcuwait_wait_event\n \n rcuwait_wake_up [UAF]\n\nNote that rcuwait_wait_event() in T3 does not block because refcount was\nalready dropped by T1. At this point T3 can exit and free the mm causing\nUAF in T1.\n\nTo avoid this we move vma->vm_mm verification into vma_start_read() and\ngrab vma->vm_mm to stabilize it before vma_refcount_put() operation.\n\n[surenb@google.com: v3]" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerable path is entered from the architecture user page-fault handler (`lock_vma_under_rcu()`), `madvise()`/`userfaultfd`/`process_vm` paths, and `/proc/pid/maps` traversal — all require local code execution. No remote peer can drive the mmap/munmap/exit sequence needed for the race.\nAC:L - The attacker controls every side of the race — the page-faulting thread, the thread unmapping the VMA, and the second process that recycles the VMA slab object and then exits to free its mm — and can spray VMA allocations and retry the loop indefinitely across CPUs. Although the window is narrow, no condition lies outside the attacker's influence.\nPR:L - Any unprivileged local process can reach the code simply by taking a page fault or reading `/proc/pid/maps`; no capability, namespace privilege, or configuration gate exists on the path.\nUI:N - The attacker drives the entire sequence with its own threads and child processes; no victim action is required.\nS:U - The use-after-free corrupts kernel memory within the same security authority; there is no VM, IOMMU, or sandbox boundary crossed.\nC:H - The freed `mm_struct` is read after being returned to `mm_cachep` and potentially reallocated, and the resulting UAF on a core mm object combined with the `wake_up_process()` primitive gives the attacker a path to arbitrary kernel memory disclosure.\nI:H - `rcuwait_wake_up()` loads a `task_struct *` out of freed, attacker-groomable memory and passes it to `wake_up_process()`, which writes into that object and dispatches through `p->sched_class->enqueue_task()` — an attacker-controlled indirect call yielding arbitrary write and control-flow hijack.\nA:H - Even without successful grooming, dereferencing a freed `mm_struct` and waking a bogus task pointer corrupts scheduler state and causes a kernel oops or panic, and the race can be retried in a loop." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "include/linux/mmap_lock.h", "mm/mmap_lock.c" ], "versions": [ { "version": "3104138517fc66aad21f4a2487bb572e9fc2e3ec", "lessThan": "6e88fe54721dee17d3496bc998f0c7d243896348", "status": "affected", "versionType": "git" }, { "version": "3104138517fc66aad21f4a2487bb572e9fc2e3ec", "lessThan": "1bcd236a2536a451e385f8d6d2bb589689ec812f", "status": "affected", "versionType": "git" }, { "version": "3104138517fc66aad21f4a2487bb572e9fc2e3ec", "lessThan": "9bbffee67ffd16360179327b57f3b1245579ef08", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "include/linux/mmap_lock.h", "mm/mmap_lock.c" ], "versions": [ { "version": "6.15", "status": "affected" }, { "version": "0", "lessThan": "6.15", "status": "unaffected", "versionType": "semver" }, { "version": "6.15.10", "lessThanOrEqual": "6.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.16.1", "lessThanOrEqual": "6.16.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.17", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "6.15.10" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "6.16.1" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "6.17" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/6e88fe54721dee17d3496bc998f0c7d243896348" }, { "url": "https://git.kernel.org/stable/c/1bcd236a2536a451e385f8d6d2bb589689ec812f" }, { "url": "https://git.kernel.org/stable/c/9bbffee67ffd16360179327b57f3b1245579ef08" } ], "title": "mm: fix a UAF when vma->mm is freed after vma->vm_refcnt got dropped", "x_generator": { "engine": "bippy-1.2.0" } } } }