CVE-2026-89532

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

svcrdma: Fix pclforeach_segment for empty chunks

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

pclforeach_segment computes its inclusive upper bound as

&chunk->chsegments[chsegcount - 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 svcrdmasegment) stride until it faults.

A zero-segcount chunk is reachable from the wire:

xdrcheckwrite_chunk() only rejects segcount values greater than

rcmaxpages, and pclalloc_write() links a freshly allocated chunk

onto rcwritepcl/rcreplypcl 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, svcrdmagetinvrkey() iterates all four

PCLs with pclforeachsegment and dereferences segment->rshandle

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

and a general protection fault.

    xdrcheckwritelist / xdrcheckreplychunk

      pclallocwrite()

        chunk = pclallocchunk(...)  / ch_segcount = 0 /

        listaddtail(&chunk->chlist, &pcl->clchunks)

        / fill loop iterates zero times for wire segcount 0 /

    svcrdmagetinvrkey()

      pclforeachchunk(rcwrite_pcl)

        pclforeach_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

chsegcount directly. For chsegcount == 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/svcrdmarecvfrom.c and

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

so no caller changes are needed.