CVE-2021-46988
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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.
Available Exploits
Related News
Affected Products
Affected Versions:
GitHub Security Advisories
Community-driven vulnerability intelligence from GitHub
Advisory Details
CVSS Scoring
CVSS Score
CVSS Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
References
Advisory provided by GitHub Security Advisory Database. Published: February 28, 2024, Modified: December 24, 2024