CVE-2026-89532

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

svcrdma: Fix pcl_for_each_segment for empty chunks

When a parsed chunk list contains a chunk whose ch_segcount is zero,

pcl_for_each_segment computes its inclusive upper bound as

&chunk->ch_segments[ch_segcount - 1]. ch_segcount is u32, so the

subtraction wraps to 0xFFFFFFFF and the bound lands far past the

ch_segments flex array. The loop body then walks unrelated memory at

sizeof(struct svc_rdma_segment) stride until it faults.

A zero-segcount chunk is reachable from the wire:

xdr_check_write_chunk() only rejects segcount values greater than

rc_maxpages, and pcl_alloc_write() links a freshly allocated chunk

onto rc_write_pcl/rc_reply_pcl before its segment-fill loop runs,

so a Write or Reply chunk advertising zero segments leaves

ch_segcount == 0 on the list. When the transport has negotiated

Send-With-Invalidate, svc_rdma_get_inv_rkey() iterates all four

PCLs with pcl_for_each_segment and dereferences segment->rs_handle

on each iteration, turning the underflow into an out-of-bounds read

and a general protection fault.

xdr_check_write_list / xdr_check_reply_chunk

pcl_alloc_write()

chunk = pcl_alloc_chunk(...) /* ch_segcount = 0 */

list_add_tail(&chunk->ch_list, &pcl->cl_chunks)

/* fill loop iterates zero times for wire segcount 0 */

svc_rdma_get_inv_rkey()

pcl_for_each_chunk(rc_write_pcl)

pcl_for_each_segment(segment, chunk)

pos <= &ch_segments[0u - 1u] /* 0xFFFFFFFF */

segment->rs_handle /* OOB read -> GPF */

Fix by switching the macro to a half-open upper bound that uses

ch_segcount directly. For ch_segcount == 0 the loop start equals the

loop end and the body is skipped; for ch_segcount > 0 the iteration

range is unchanged. All six existing call sites in

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c and

net/sunrpc/xprtrdma/svc_rdma_rw.c remain correct under the new bound,

so no caller changes are needed.