{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-99264", "modified": "2026-11-04T05:30:01Z", "upstream": [ "CVE-2026-99264" ], "published": "2026-11-03T11:48:51Z", "summary": "io_uring/net: don't retry recv on uncommitted buffers", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/net: don't retry recv on uncommitted buffers\n\nCommit 41b70df5b38b (\"io_uring/net: commit partial buffers on retry\")\ncommits ring provided buffers when a receive is going to be retried after\na partial transfer, so that another request using the same buffer group\ncan't be handed the memory the first one keeps receiving into. It commits\nthe number of bytes received so far. That does the job for a single\nbuffer which is consumed as a whole, but the request hangs on to all it\nhas mapped:\n\n- For a buffer ring with IOU_PBUF_RING_INC only these bytes are consumed.\n The rest of the buffer stays at the head of the ring.\n- For a bundle only the buffers which hold these bytes are consumed, the\n others that were peeked stay in the ring.\n\nIn both cases the next receive with that buffer group gets memory that\nthe retried request is still going to write to, and whoever comes last\noverwrites the data of the other. What the retry fills isn't committed at\nall, as the buffer list isn't known any more at that point. So the kernel\nhands it out again later on, while the CQE tells the application that it\nwas used, and for an incremental buffer that it is done with.\n\nThe remainder can't be committed in advance: if the request ends up\nreceiving less, there is no way to tell the application that more was\nconsumed than the CQE accounts for. Complete the request with what it has\ngot instead of retrying it. MSG_WAITALL is no longer honoured for\nreceives into incremental buffers or multi buffer bundles, they can\nreturn a short count, with the request marked as failed like for other\nshort MSG_WAITALL transfers.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.12.47-1+rpt1~bookworm", "1:6.12.62-1+rpt1~bookworm", "1:6.12.75-1+rpt1~bookworm", "1:6.12.87-1+rpt1~bookworm", "1:6.12.93-1+rpt1", "1:6.12.96-1+rpt1", "1:6.12.109-1+rpt1" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.12.47+rpt-rpi-2712", "binary_version": "1:6.12.47-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.47+rpt-rpi-v6", "binary_version": "1:6.12.47-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.47+rpt-rpi-v7", "binary_version": "1:6.12.47-1+rpt1~bookworm" }, { "binary_name": "linux-image-6.12.47+rpt-rpi-v7l", "binary_version": 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"url": "https://git.kernel.org/stable/c/fc8506eea4498ecba26ef8bf6dbbd74af3dc891d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/97b8dc36ba3cb176b74a7929140aeaeb40d5cdc0" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/8444de681a179e41a4eb92d5bbe770a0677074a6" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-11-03T19:14:48Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The defect is in io_recv()/io_recvmsg(), reached from io_uring_enter() via io_init_req()/io_issue_sqe() on IORING_OP_RECV/RECVMSG with IOSQE_BUFFER_SELECT. io_net_kbuf_recyle() under-commits an IOU_PBUF_RING_INC tail or unused bundle buffers; a peer can supply socket bytes that fill them, but cannot register that pbuf ring or set those SQE flags.\nAC:L - The attacker owns both ends of a SOCK_STREAM socketpair, registers IOU_PBUF_RING_INC or a multi-buffer bundle, and submits a MSG_WAITALL recv larger than the first write so sock_recvmsg() returns a short count. io_net_retry() then takes io_net_kbuf_recyle(), and a second recv on the same bgid aliases the uncommitted remainder with no uncontrolled race.\nPR:L - io_uring_setup() only calls io_uring_allowed(); sysctl_io_uring_disabled defaults to 0, so an unprivileged user can create a ring. io_register_pbuf_ring() (IORING_REGISTER_PBUF_RING) and io_recv()/io_recvmsg() have no capability check; IOSQE_BUFFER_SELECT plus MSG_WAITALL needs no CAP_* or user-namespace trick.\nUI:N - The attacking process itself performs io_uring_setup(), io_uring_register(IORING_REGISTER_PBUF_RING), and io_uring_enter() of the MSG_WAITALL recv on its own ring and sockets. No other user must mount, open, or otherwise interact.\nS:U - The aliased sock_recvmsg() writes stay in the same process's provided-buffer userspace and in the host io_uring authority. This is not a VM, IOMMU, or sandbox-boundary escape.\nC:H - io_kbuf_commit()/io_kbuf_inc_commit() consume only the first short recv, while the retried request keeps its iov_iter; a second io_recv() on that bgid is then given the leftover INC tail or unconsumed bundle buffers. Socket data from another connection in the group lands in that shared memory, and the completing CQE omits IORING_CQE_F_BUF_MORE so the app reclaims a buffer the kernel is still filling.\nI:H - After io_net_kbuf_recyle() the retried io_recv()/io_recvmsg() keeps writing through the original iov_iter into bytes already handed back to the ring, and the next select maps those same addresses. The last writer overwrites the other, including into memory the application reused after a CQE that reported the incremental buffer done, which is a write-into-reclaimed-buffer primitive.\nA:H - The same double mapping lets sock_recvmsg() keep storing into a buffer the CQE already released; once the application recycles that region, the in-flight write corrupts its heap and can crash the io_uring consumer. The attacker can repeat the short MSG_WAITALL recv plus second bgid select at will." } } }