{"id":"CVE-2025-40007","summary":"netfs: fix reference leak","details":"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.","modified":"2026-04-02T12:48:14.689354Z","published":"2025-10-20T15:26:53.880Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/40xxx/CVE-2025-40007.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/4d428dca252c858bfac691c31fa95d26cd008706"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8df142e93098b4531fadb5dfcf93087649f570b3"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/40xxx/CVE-2025-40007.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-40007"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"20d72b00ca814d748f5663484e5c53bb2bf37a3a"},{"fixed":"8df142e93098b4531fadb5dfcf93087649f570b3"},{"fixed":"4d428dca252c858bfac691c31fa95d26cd008706"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"0"},{"last_affected":"1a8360c2eed3b292ed654c2ac61b09de4a80e298"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-40007.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.16.0"},{"fixed":"6.16.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-40007.json"}}],"schema_version":"1.7.5"}