CVE-2026-98116 (GCVE-0-2026-98116)
Vulnerability from cvelistv5
Published
2026-09-25 10:36
Modified
2026-10-19 09:14
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF snd_pcm_hw_params() and snd_pcm_hw_free() guard buffer reallocation with an mmap_count check performed under the PCM stream lock, but the lock is released long before the buffer is actually freed: snd_pcm_sync_stop(), constraint refinement and do_free_pages() all happen in between. snd_pcm_mmap_data(), on the other hand, takes no lock at all: it validates against the old buffer's state and dma_bytes, remaps its pages into the VMA, and only then increments mmap_count. A concurrent mmap() can therefore slip in between the check and the free. remap_pfn_range() installs writable PTEs for the old buffer's pages without taking page references, and the subsequent do_free_pages() returns those pages to the page allocator while the VMA still maps them. This leaves a stale, writable mapping of freed pages: a page-level use-after-free that can be leveraged for local privilege escalation. Make snd_pcm_mmap_data() participate in the buffer-access scheme introduced for hw_params/hw_free: acquire runtime->buffer_accessing before validating and remapping, and release it afterwards. Buffer reallocation already fails with -EBUSY while accessors are active, and the mmap side now fails with -EBUSY while a reallocation is in progress, so the validate/remap sequence and the check/free sequence can no longer interleave. A reproducer that turns this race into a stale writable mapping of the freed DMA buffer pages is available on request.
References
Impacted products
Vendor Product Version
Linux Linux Version: 33061d0fba51d2bf70a2ef9645f703c33fe8e438
Version: 92ee3c60ec9fe64404dc035e7c41277d74aa26cb
Version: 92ee3c60ec9fe64404dc035e7c41277d74aa26cb
Version: 92ee3c60ec9fe64404dc035e7c41277d74aa26cb
Version: 92ee3c60ec9fe64404dc035e7c41277d74aa26cb
Version: 92ee3c60ec9fe64404dc035e7c41277d74aa26cb
Version: 92ee3c60ec9fe64404dc035e7c41277d74aa26cb
Version: a42aa926843acca96c0dfbde2e835b8137f2f092
Version: 9cb6c40a6ebe4a0cfc9d6a181958211682cffea9
Version: fbeb492694ce0441053de57699e1e2b7bc148a69
Version: 0f6947f5f5208f6ebd4d76a82a4757e2839a23f8
Version: 0090c13cbbdffd7da079ac56f80373a9a1be0bf8
Version: 1bbf82d9f961414d6c76a08f7f843ea068e0ab7b
Version: 5.15.32   ≤
Version: 4.14.279   ≤
Version: 4.19.243   ≤
Version: 5.4.193   ≤
Version: 5.10.109   ≤
Version: 5.16.18   ≤
Version: 5.17.1   ≤
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF\n\nsnd_pcm_hw_params() and snd_pcm_hw_free() guard buffer reallocation\nwith an mmap_count check performed under the PCM stream lock, but the\nlock is released long before the buffer is actually freed:\nsnd_pcm_sync_stop(), constraint refinement and do_free_pages() all\nhappen in between.  snd_pcm_mmap_data(), on the other hand, takes no\nlock at all: it validates against the old buffer\u0027s state and\ndma_bytes, remaps its pages into the VMA, and only then increments\nmmap_count.\n\nA concurrent mmap() can therefore slip in between the check and the\nfree.  remap_pfn_range() installs writable PTEs for the old buffer\u0027s\npages without taking page references, and the subsequent\ndo_free_pages() returns those pages to the page allocator while the\nVMA still maps them.  This leaves a stale, writable mapping of freed\npages: a page-level use-after-free that can be leveraged for local\nprivilege escalation.\n\nMake snd_pcm_mmap_data() participate in the buffer-access scheme\nintroduced for hw_params/hw_free: acquire runtime-\u003ebuffer_accessing\nbefore validating and remapping, and release it afterwards.  Buffer\nreallocation already fails with -EBUSY while accessors are active,\nand the mmap side now fails with -EBUSY while a reallocation is in\nprogress, so the validate/remap sequence and the check/free sequence\ncan no longer interleave.\n\nA reproducer that turns this race into a stale writable mapping of\nthe freed DMA buffer pages is available on request."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is triggered by mmap() on a local /dev/snd/pcmC*D* file descriptor (snd_pcm_mmap -\u003e snd_pcm_mmap_data) racing with SNDRV_PCM_IOCTL_HW_PARAMS/HW_FREE ioctls on the same fd. No remote protocol carries any of the inputs.\nAC:L - One process controls both sides of the race: one thread calls mmap() and another calls hw_free/hw_params. The window runs from the mmap_count check under the stream lock through snd_pcm_sync_stop and refinement to do_free_pages, and the attacker can retry as often as needed.\nPR:L - Opening the PCM device node takes ordinary local user access, either the audio group or the udev uaccess ACL given to the logged-in seat user. No capability is checked on the mmap or hw_params/hw_free paths.\nUI:N - The attacker opens the device, sets hw_params and races the mmap against hw_free entirely through their own syscalls. No other user has to do anything.\nS:U - This is a local kernel privilege escalation within the same kernel security authority. It crosses no VM or IOMMU boundary.\nC:H - remap_pfn_range installs PTEs for the old DMA buffer pages without taking page references, and do_free_pages then frees them. The attacker keeps a direct mapping of whatever the page allocator reuses those pages for, such as page tables, cred or slab pages, and can read it.\nI:H - The stale mapping of the freed buffer pages is writable, which gives direct write access to reallocated kernel pages. This is a page-level UAF that enables privilege escalation, as the fix commit itself states.\nA:H - Writing through the stale PTEs into pages that have been reallocated corrupts arbitrary kernel memory, which leads to oopses, panics or page-state BUGs."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:14:08.504Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/e6cdd2a0470d64073349a970dc1691433804b271"
        },
        {
          "url": "https://git.kernel.org/stable/c/9857a75714bb5df4781e4d8b1a1753b1e17bf07a"
        },
        {
          "url": "https://git.kernel.org/stable/c/cbadf2575d25e7dcc0d4da2717817ae569fbc99b"
        },
        {
          "url": "https://git.kernel.org/stable/c/cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5"
        },
        {
          "url": "https://git.kernel.org/stable/c/fd137bf8149bc6460f9b7b1fc292025da04cb9ee"
        },
        {
          "url": "https://git.kernel.org/stable/c/8c1882dfee8f404d118020664b73eb4592172226"
        },
        {
          "url": "https://git.kernel.org/stable/c/9b110a9dcecc59516c77cb3c0caf1f492f75df2d"
        }
      ],
      "title": "ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98116",
    "datePublished": "2026-09-25T10:36:01.723Z",
    "dateReserved": "2026-09-25T10:25:14.317Z",
    "dateUpdated": "2026-10-19T09:14:08.504Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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