{"cve":"CVE-2025-40007","nvd":{"published":"2025-10-20T16:15:37.357","modified":"2026-10-19T21:10:00.160","status":"Deferred","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfs: fix reference leak\n\nCommit 20d72b00ca81 (\"netfs: Fix the request's work item to not\nrequire a ref\") modified netfs_alloc_request() to initialize the\nreference counter to 2 instead of 1.  The rationale was that the\nrequet's \"work\" would release the second reference after completion\n(via netfs_{read,write}_collection_worker()).  That works most of the\ntime if all goes well.\n\nHowever, it leaks this additional reference if the request is released\nbefore the I/O operation has been submitted: the error code path only\ndecrements the reference counter once and the work item will never be\nqueued because there will never be a completion.\n\nThis has caused outages of our whole server cluster today because\ntasks were blocked in netfs_wait_for_outstanding_io(), leading to\ndeadlocks in Ceph (another bug that I will address soon in another\npatch).  This was caused by a netfs_pgpriv2_begin_copy_to_cache() call\nwhich failed in fscache_begin_write_operation().  The leaked\nnetfs_io_request was never completed, leaving `netfs_inode.io_count`\nwith a positive value forever.\n\nAll of this is super-fragile code.  Finding out which code paths will\nlead to an eventual completion and which do not is hard to see:\n\n- Some functions like netfs_create_write_req() allocate a request, but\n  will never submit any I/O.\n\n- netfs_unbuffered_read_iter_locked() calls netfs_unbuffered_read()\n  and then netfs_put_request(); however, netfs_unbuffered_read() can\n  also fail early before submitting the I/O request, therefore another\n  netfs_put_request() call must be added there.\n\nA rule of thumb is that functions that return a `netfs_io_request` do\nnot submit I/O, and all of their callers must be checked.\n\nFor my taste, the whole netfs code needs an overhaul to make reference\ncounting easier to understand and less fragile & obscure.  But to fix\nthis bug here and now and produce a patch that is adequate for a\nstable backport, I tried a minimal approach that quickly frees the\nrequest object upon early failure.\n\nI decided against adding a second netfs_put_request() each time\nbecause that would cause code duplication which obscures the code\nfurther.  Instead, I added the function netfs_put_failed_request()\nwhich frees such a failed request synchronously under the assumption\nthat the reference count is exactly 2 (as initially set by\nnetfs_alloc_request() and never touched), verified by a\nWARN_ON_ONCE().  It then deinitializes the request object (without\ngoing through the \"cleanup_work\" indirection) and frees the allocation\n(with RCU protection to protect against concurrent access by\nnetfs_requests_seq_start()).\n\nAll code paths that fail early have been changed to call\nnetfs_put_failed_request() instead of netfs_put_request().\nAdditionally, I have added a netfs_put_request() call to\nnetfs_unbuffered_read() as explained above because the\nnetfs_put_failed_request() approach does not work there.","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/4d428dca252c858bfac691c31fa95d26cd008706","https://git.kernel.org/stable/c/8df142e93098b4531fadb5dfcf93087649f570b3"],"products":[],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2025-40007","score":0.00225,"percentile":0.12999,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}