| From bippy-1.2.0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@kernel.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2025-37999: fs/erofs/fileio: call erofs_onlinefolio_split() after bio_add_folio() |
| |
| Description |
| =========== |
| |
| 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. |
| |
| The Linux kernel CVE team has assigned CVE-2025-37999 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.12 with commit ce63cb62d794c98c7631c2296fa845f2a8d0a4a1 and fixed in 6.12.29 with commit 61e0fc3312309867e5a3495329dad0286d2a5703 |
| Issue introduced in 6.12 with commit ce63cb62d794c98c7631c2296fa845f2a8d0a4a1 and fixed in 6.14.7 with commit c26076197df348c84cc23e5962d61902e072a0f5 |
| Issue introduced in 6.12 with commit ce63cb62d794c98c7631c2296fa845f2a8d0a4a1 and fixed in 6.15 with commit bbfe756dc3062c1e934f06e5ba39c239aa953b92 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2025-37999 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| fs/erofs/fileio.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/61e0fc3312309867e5a3495329dad0286d2a5703 |
| https://git.kernel.org/stable/c/c26076197df348c84cc23e5962d61902e072a0f5 |
| https://git.kernel.org/stable/c/bbfe756dc3062c1e934f06e5ba39c239aa953b92 |
