Vulnerability 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Linux | Linux Kernel | >= 4.11, < 4.14.233 |
Related Weaknesses (CWE)
References
- https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1fPatch
- https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744dePatch
- https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6Patch
- https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69Patch
- https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171cPatch
- https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330Patch
- https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43Patch
- https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1fPatch
- https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744dePatch
- https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6Patch
- https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69Patch
- https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171cPatch
- https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330Patch
- https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43Patch
FAQ
What is CVE-2021-46988?
CVE-2021-46988 is a vulnerability with a CVSS score of 5.5 (MEDIUM). 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 ioc...
How severe is CVE-2021-46988?
CVE-2021-46988 has been rated MEDIUM with a CVSS base score of 5.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2021-46988?
Check the references section above for vendor advisories and patch information. Affected products include: Linux Linux Kernel.