svcrdma: Fix offset arithmetic in read_chunk_range

Overview

In the Linux kernel, the following vulnerability has been resolved:

svcrdma: Fix offset arithmetic in read_chunk_range

svc_rdma_read_chunk_range() walks a Read chunk's segment list to build a sub-range starting at byte offset and spanning length bytes for a Position-Zero or Call chunk. Two arithmetic defects in the per-segment loop produce wrong DMA lengths and a u32 underflow:

pcl_for_each_segment(segment, chunk) {
        if (offset > segment->rs_length) {
                offset -= segment->rs_length;
                continue;
        }

        dummy.rs_handle = segment->rs_handle;
        dummy.rs_length = min_t(u32, length,
                                segment->rs_length) - offset;
        dummy.rs_offset = segment->rs_offset + offset;

First, the skip predicate uses '>' instead of '>='. When offset equals the segment's full rs_length, the segment is fully consumed and should be skipped, but the loop falls through into the body. The resulting dummy.rs_length is min_t(u32, length, rs_length) - rs_length, which underflows to a near-UINT_MAX u32 when length is smaller than rs_length, or is zero otherwise.

Second, the length formula subtracts offset from the min_t() result rather than from segment->rs_length before the cap. For offset > 0 the segment's residual is rs_length - offset, not rs_length, so the cap must be applied to the residual. With the current bracketing, whenever length is smaller than rs_length - offset the per-segment length becomes length - offset instead of length, silently dropping offset bytes from the rebuilt chunk. Combined with the boundary case above it also enables the u32 underflow path, which propagates a huge nr_bvec into svc_rdma_build_read_segment() and a multi-MiB kmalloc_array_node() in svc_rdma_get_rw_ctxt().

Additionally, svc_rdma_read_call_chunk() can invoke this function with length == 0 when the last Read chunk ends exactly at the end of the Call chunk. With the corrected >= predicate, every segment is skipped and the function returns the initial -EINVAL, rejecting a valid request. Return success immediately when length is zero. Also break out of the loop once length is fully consumed to avoid passing zero-length segments to svc_rdma_build_read_segment().

Fix by using '>=' so a fully-consumed segment is skipped, by moving '- offset' inside min_t() so the cap is applied to the segment's residual length, by returning success for zero-length requests, and by stopping iteration when the requested range has been consumed.

Affected

• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < 10873311f91db9454e2fadbf9866bc819e0646d9
• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < addbf02dfe3b25e7e38e03bbd4e2a6ed86a14be7
• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < cba8543c18cf42fd80fd63effb6df6ff4f7e73ce
• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < 6ee4dc7476b3abc92ec1d444533a559f33f59561
• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < a46b35f213c2426f5d6a0458a8f7e873fc59cdfd
• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < 4493c96bbd0068fadf69cbae8d13426202e34cdc
• Linux >= d7cc73972661be4a02a1b09f1d9b3283c6c05154 < 4a44c140cc2f3643a39e258bb0c0ab9d0f494f5e
• Linux 5.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-14 · vex