{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-72473", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-72473" ], "published": "2026-08-15T06:04:33Z", "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 > 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->rl_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 >= 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() ->\n xprt_rdma_free_slot() -> 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.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.178", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-72473" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/740975054a1970c0cf15f70ac39724a064f45847" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/9f3d9b68c1c6c51746e5ecdb52b2e6a2901de37e" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/e7632089523acddcdd8f090ad19e96fb3107b04d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/53442c7d0c888e51b8bc3da196970a669cc6b294" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/8203f760a72bd39a3b66bc4eff0aa272a99fe22b" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/e786233d2e0bbff9a82e43f02ae3a46ab4b08ec3" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-17T05:50:24Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 9.8, "cvss_v3_severity": "Critical", "scenario": "AV:N - The bug is in the RPC-over-RDMA client (xprtrdma); a remote NFS/RDMA peer delivers Receive completions that invoke rpcrdma_reply_handler() over InfiniBand/RoCE/iWARP, so exploitation is via network protocol traffic from a malicious or compromised server.\nAC:L - For inline Sends using only pre-registered buffers (sc_unmap_count==0), the reply path completes the RPC and returns the req to the free pool before Send completion; a remote peer can reliably trigger this by replying immediately to normal small NFS RPCs.\nPR:N - Exploitation requires no privileges on the victim host; a remote malicious or compromised NFS/RDMA server can send crafted/fast replies over the established RDMA connection to drive the vulnerable completion path.\nUI:N - No end-user interaction is needed at exploit time; once a host uses NFS-over-RDMA, triggering the bug is automatic during ordinary client I/O against the attacker-controlled server.\nS:U - The flaw causes kernel heap UAF/DMA corruption within the NFS client's kernel context and does not by itself cross hypervisor, VM, or sandbox security boundaries.\nC:H - Recycling rpcrdma_req while the HCA may still DMA-read its send buffers is a use-after-free that can expose or leak kernel memory when the slot is reallocated and buffers are reused under active DMA.\nI:H - Premature return of rpcrdma_req to rb_send_bufs while Send WRs are in flight permits heap corruption and typical UAF exploitation paths for arbitrary kernel memory writes or control-flow hijack.\nA:H - Concurrent DMA against freed/reused request buffers can provoke kernel oops/panic or wedged RPC/RDMA transport state, giving high availability impact on NFS-over-RDMA clients." } } }