{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-40007","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2025-04-16T07:20:57.151Z","datePublished":"2025-10-20T15:26:53.880Z","dateUpdated":"2026-05-11T21:40:40.456Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-05-11T21:40:40.456Z"},"descriptions":[{"lang":"en","value":"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."}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/netfs/buffered_read.c","fs/netfs/direct_read.c","fs/netfs/direct_write.c","fs/netfs/internal.h","fs/netfs/objects.c","fs/netfs/read_pgpriv2.c","fs/netfs/read_single.c","fs/netfs/write_issue.c"],"versions":[{"version":"20d72b00ca814d748f5663484e5c53bb2bf37a3a","lessThan":"8df142e93098b4531fadb5dfcf93087649f570b3","status":"affected","versionType":"git"},{"version":"20d72b00ca814d748f5663484e5c53bb2bf37a3a","lessThan":"4d428dca252c858bfac691c31fa95d26cd008706","status":"affected","versionType":"git"},{"version":"1a8360c2eed3b292ed654c2ac61b09de4a80e298","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/netfs/buffered_read.c","fs/netfs/direct_read.c","fs/netfs/direct_write.c","fs/netfs/internal.h","fs/netfs/objects.c","fs/netfs/read_pgpriv2.c","fs/netfs/read_single.c","fs/netfs/write_issue.c"],"versions":[{"version":"6.16","status":"affected"},{"version":"0","lessThan":"6.16","status":"unaffected","versionType":"semver"},{"version":"6.16.10","lessThanOrEqual":"6.16.*","status":"unaffected","versionType":"semver"},{"version":"6.17","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.16.10"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.17"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15.3"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/8df142e93098b4531fadb5dfcf93087649f570b3"},{"url":"https://git.kernel.org/stable/c/4d428dca252c858bfac691c31fa95d26cd008706"}],"title":"netfs: fix reference leak","x_generator":{"engine":"bippy-1.2.0"}}}}