In the Linux kernel, the following vulnerability has been resolved:
fs/erofs/fileio: call erofs_onlinefolio_split() after bio_add_folio()
If bio_add_folio() fails (because it is full),
erofs_fileio_scan_folio() needs to submit the I/O request via
erofs_fileio_rq_submit() and allocate a new I/O request with an empty
struct bio. Then it retries the bio_add_folio() call.
However, at this point, erofs_onlinefolio_split() has already been
called which increments folio->private; the retry will call
erofs_onlinefolio_split() again, but there will never be a matching
erofs_onlinefolio_end() call. This leaves the folio locked forever
and all waiters will be stuck in folio_wait_bit_common().
This bug has been added by commit ce63cb62d794 ("erofs: support
unencoded inodes for fileio"), but was practically unreachable because
there was room for 256 folios in the struct bio - until commit
9f74ae8c9ac9 ("erofs: shorten bvecs[] for file-backed mounts") which
reduced the array capacity to 16 folios.
It was now trivial to trigger the bug by manually invoking readahead from userspace, e.g.:
posix_fadvise(fd, 0, st.st_size, POSIX_FADV_WILLNEED);
This should be fixed by invoking erofs_onlinefolio_split() only after bio_add_folio() has succeeded. This is safe: asynchronous completions invoking erofs_onlinefolio_end() will not unlock the folio because erofs_fileio_scan_folio() is still holding a reference to be released by erofs_onlinefolio_end() at the end.
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 6.12 | 6.12.29 |
| linux / linux_kernel | 6.13 | 6.14.7 |
| linux / linux_kernel | 6.15-rc1 | 6.15-rc1.x |
| linux / linux_kernel | 6.15-rc2 | 6.15-rc2.x |
| linux / linux_kernel | 6.15-rc3 | 6.15-rc3.x |
| linux / linux_kernel | 6.15-rc4 | 6.15-rc4.x |
| linux / linux_kernel | 6.15-rc5 | 6.15-rc5.x |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
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Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
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