CVE-2026-93228

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

svcrdma: Reject Write/Reply chunks with segcount 0

A peer can send a Write or Reply chunk whose segcount field is zero.

xdrcheckwritechunk() only rejects segcount > rcmaxpages, so zero

passes the range check, and xdrinlinedecode(stream, 0) returns the

current (non-NULL) cursor without advancing. The function returns

true and pclallocwrite() then links a struct svcrdmachunk with

chsegcount == 0 onto rcwritepcl or rcreply_pcl.

An earlier patch in this series made pclforeach_segment() safe for

ch_segcount == 0, so this no longer drives the memory walk it used

to. Rejecting the malformed frame at the decode boundary is still

worthwhile as defense in depth: it keeps degenerate zero-segment

chunks off the parsed chunk lists entirely, so any future consumer

that walks ch_segments directly cannot observe one, and it makes the

zero-floor easy to backport to trees where the macro change is more

intrusive. RFC 8166 has no meaning for a Write/Reply chunk that

describes no remote buffer, so no legitimate client is affected.

xdrcheckreply_chunk() funnels Reply chunks through

xdrcheckwrite_chunk() and inherits the same rejection.

pclallocwrite() also links each chunk onto the parsed chunk list

before filling its segment array. If a future change weakens the

segcount-0 rejection, an incomplete chunk is visible to consumers

during the fill loop. Reorder so that listaddtail() follows the

segment fill loop, ensuring only fully-populated chunks appear on

the list.