{"id":"CVE-2026-72473","summary":"xprtrdma: Decouple req recycling from RPC completion","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nxprtrdma: Decouple req recycling from RPC completion\n\nrl_kref formerly served two distinct lifetimes through a single\nrefcount: it gated when a Reply could wake its RPC task, and it\ngated when an rpcrdma_req could return to its free pool. The\nmarshal path took the Send-side reference only when SGEs needed\nDMA-unmap (sc_unmap_count \u003e 0), which made a Send carrying only\npre-registered buffers an exception: the Reply handler dropped\nrl_kref from 1 to 0 and freed the req while the HCA might still\nbe DMA-reading from its send buffer.\n\nGive rl_kref a narrower job. The RPC layer takes one reference\nwhen slot allocation hands a req out. rpcrdma_prepare_send_sges()\ntakes a Send-side reference unconditionally after WR preparation\nsucceeds. xprt_rdma_free_slot() and xprt_rdma_bc_free_rqst() drop\nthe RPC-layer reference; rpcrdma_sendctx_unmap() drops the\nSend-side reference. The req returns to its free pool only after\nboth owners have signed off.\n\nThe existing kref_init(&req-\u003erl_kref) call in\nrpcrdma_prepare_send_sges() is removed. Initialization moves to\nthe slot-allocation paths (xprt_rdma_alloc_slot and\nrpcrdma_bc_rqst_get), and the release callback re-arms rl_kref\nbefore the req returns to a free pool. A re-init in the marshal\npath would discard the RPC-layer reference that already exists\non entry.\n\nThree invariants follow:\n\n  - Any rpcrdma_req held by an rpc_rqst has rl_kref \u003e= 1.\n    xprt_rdma_alloc_slot(), rpcrdma_bc_rqst_get(), and the\n    backlog-wake branch in xprt_rdma_alloc_slot() each kref_init\n    rl_kref before publishing the req. Without this invariant,\n    an RPC task that aborts between slot allocation and marshal\n    (gss_refresh failure or signal during call_connect, for\n    example) would drive xprt_release() -\u003e\n    xprt_rdma_free_slot() -\u003e kref_put against a refcount of\n    zero, saturating refcount_t and stranding the slot.\n\n  - The Send-side reference is taken only after WR prep\n    succeeds. A mapping failure in rpcrdma_prepare_send_sges()\n    runs rpcrdma_sendctx_cancel(), which DMA-unmaps the sendctx\n    and clears sc_req without touching rl_kref. The sendctx\n    ring walks in rpcrdma_sendctx_put_locked() and\n    rpcrdma_sendctxs_destroy() skip entries with sc_req == NULL,\n    so a burst of -EIO marshal failures cannot hold reqs off\n    rb_send_bufs.\n\n  - The release callback re-arms rl_kref so the next consumer\n    enters with the invariant satisfied.\n\nReplies now complete the RPC directly. rpcrdma_reply_handler()\ncalls rpcrdma_complete_rqst() in place of kref_put on the\nnon-LocalInv branch. The LocalInv branch already completes the\nRPC from frwr_unmap_async() and is unaffected.\n\nBecause Send-side references can now outlive RPC completion,\nconnection teardown drains sendctx entries whose unsignaled\nSends never had a later signaled completion to walk the ring.\nrpcrdma_sendctxs_destroy() walks the active range and runs\nrpcrdma_sendctx_unmap() on each entry with a non-NULL sc_req\nbefore the request buffers are reset, and is moved ahead of\nrpcrdma_reqs_reset() in rpcrdma_xprt_disconnect() so the reqs\nare still in their pre-reset state when the Send-side refs are\nreleased.\n\nThe drain creates a teardown-ordering hazard on the backchannel\npath. With the new lifetime, releasing a bc_prealloc req from\nrpcrdma_req_release() re-adds it to bc_pa_list. The disconnect\nin xprt_rdma_destroy() runs after xprt_destroy_backchannel() has\nalready emptied bc_pa_list, so the drained reqs would otherwise\nleak. xprt_rdma_destroy() now runs xprt_rdma_bc_destroy(xprt, 0)\na second time after the disconnect to reclaim them.","modified":"2026-08-18T04:17:29.339802503Z","published":"2026-08-15T05:57:14.412Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72473.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/53442c7d0c888e51b8bc3da196970a669cc6b294"},{"type":"WEB","url":"https://git.kernel.org/stable/c/740975054a1970c0cf15f70ac39724a064f45847"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8203f760a72bd39a3b66bc4eff0aa272a99fe22b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9f3d9b68c1c6c51746e5ecdb52b2e6a2901de37e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e7632089523acddcdd8f090ad19e96fb3107b04d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e786233d2e0bbff9a82e43f02ae3a46ab4b08ec3"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/72xxx/CVE-2026-72473.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72473"},{"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":"0ab115237025f5e379620bbcd56a02697d07b002"},{"fixed":"740975054a1970c0cf15f70ac39724a064f45847"},{"fixed":"9f3d9b68c1c6c51746e5ecdb52b2e6a2901de37e"},{"fixed":"e7632089523acddcdd8f090ad19e96fb3107b04d"},{"fixed":"53442c7d0c888e51b8bc3da196970a669cc6b294"},{"fixed":"8203f760a72bd39a3b66bc4eff0aa272a99fe22b"},{"fixed":"e786233d2e0bbff9a82e43f02ae3a46ab4b08ec3"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-72473.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.3.0"},{"fixed":"6.1.178"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.145"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.97"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.40"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.5"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-72473.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}