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CVE-2026-98116

ALSA: pcm: Serialize PCM mmap with buffer reallocation to fix page UAF

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.15.222, 4.15, 4.20, 5.5, 5.11, and 7 more
None on Exploit-DB, Metasploit or GitHub

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.

Timeline

  1. CVE published
  2. Record last updated

Affected versions

  • Linux Linux

    From 33061d0fba51d2bf70a2ef9645f703c33fe8e438 · fixed in e6cdd2a0470d64073349a970dc1691433804b271; From 92ee3c60ec9fe64404dc035e7c41277d74aa26cb · fixed in 9857a75714bb5df4781e4d8b1a1753b1e17bf07a; From 92ee3c60ec9fe64404dc035e7c41277d74aa26cb · fixed in cbadf2575d25e7dcc0d4da2717817ae569fbc99b; From 92ee3c60ec9fe64404dc035e7c41277d74aa26cb · fixed in cbc7ec97601d09b74e05e44470fa6b0bcdabf3f5; From 92ee3c60ec9fe64404dc035e7c41277d74aa26cb · fixed in fd137bf8149bc6460f9b7b1fc292025da04cb9ee; From 92ee3c60ec9fe64404dc035e7c41277d74aa26cb · fixed in 8c1882dfee8f404d118020664b73eb4592172226; From 92ee3c60ec9fe64404dc035e7c41277d74aa26cb · fixed in 9b110a9dcecc59516c77cb3c0caf1f492f75df2d; From 5.15.32 · fixed in 5.15.222; From 4.14.279 · fixed in 4.15; From 4.19.243 · fixed in 4.20; From 5.4.193 · fixed in 5.5; From 5.10.109 · fixed in 5.11; From 5.16.18 · fixed in 5.17; From 5.17.1 · fixed in 5.18

  • Linux Linux

    5.18

  • KernelLinux

    fixed in 5.15.222; From 5.16.0 · fixed in 6.1.189; From 5.18.0 · fixed in 6.6.158; From 6.2.0 · fixed in 6.12.111; From 6.7.0 · fixed in 6.18.53; From 6.13.0 · fixed in 7.2.7

References 7

git.kernel.org