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Ubuntu: (CVE-2021-46988): linux vulnerability

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Ubuntu: (CVE-2021-46988): linux vulnerability

Severity
5
CVSS
(AV:L/AC:L/Au:S/C:N/I:N/A:C)
Published
02/28/2024
Created
11/21/2024
Added
11/19/2024
Modified
02/11/2025

Description

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: release page in error path to avoid BUG_ON Consider the following sequence of events: 1. Userspace issues a UFFD ioctl, which ends up calling into shmem_mfill_atomic_pte(). We successfully account the blocks, we shmem_alloc_page(), but then the copy_from_user() fails. We return -ENOENT. We don't release the page we allocated. 2. Our caller detects this error code, tries the copy_from_user() after dropping the mmap_lock, and retries, calling back into shmem_mfill_atomic_pte(). 3. Meanwhile, let's say another process filled up the tmpfs being used. 4. So shmem_mfill_atomic_pte() fails to account blocks this time, and immediately returns - without releasing the page. This triggers a BUG_ON in our caller, which asserts that the page should always be consumed, unless -ENOENT is returned. To fix this, detect if we have such a "dangling" page when accounting fails, and if so, release it before returning.

Solution(s)

  • ubuntu-upgrade-linux
  • ubuntu-upgrade-linux-aws
  • ubuntu-upgrade-linux-aws-5-4
  • ubuntu-upgrade-linux-aws-fips
  • ubuntu-upgrade-linux-aws-hwe
  • ubuntu-upgrade-linux-azure
  • ubuntu-upgrade-linux-azure-4-15
  • ubuntu-upgrade-linux-azure-5-4
  • ubuntu-upgrade-linux-azure-fips
  • ubuntu-upgrade-linux-bluefield
  • ubuntu-upgrade-linux-fips
  • ubuntu-upgrade-linux-gcp
  • ubuntu-upgrade-linux-gcp-4-15
  • ubuntu-upgrade-linux-gcp-5-4
  • ubuntu-upgrade-linux-gcp-fips
  • ubuntu-upgrade-linux-gkeop
  • ubuntu-upgrade-linux-hwe
  • ubuntu-upgrade-linux-hwe-5-4
  • ubuntu-upgrade-linux-kvm
  • ubuntu-upgrade-linux-oracle
  • ubuntu-upgrade-linux-oracle-5-4
  • ubuntu-upgrade-linux-raspi
  • ubuntu-upgrade-linux-raspi-5-4

References

  • https://attackerkb.com/topics/cve-2021-46988
  • CVE - 2021-46988
  • https://git.kernel.org/linus/7ed9d238c7dbb1fdb63ad96a6184985151b0171c
  • https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f
  • https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de
  • https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6
  • https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69
  • https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c
  • https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330
  • https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43
  • https://www.cve.org/CVERecord?id=CVE-2021-46988
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