6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chris Mason [ Upstream commit 9808eb7656666acc7291bae9ab6b987bd16e47e0 ] A peer can send a Write or Reply chunk whose segcount field is zero. xdr_check_write_chunk() only rejects segcount > rc_maxpages, so zero passes the range check, and xdr_inline_decode(stream, 0) returns the current (non-NULL) cursor without advancing. The function returns true and pcl_alloc_write() then links a struct svc_rdma_chunk with ch_segcount == 0 onto rc_write_pcl or rc_reply_pcl. An earlier patch in this series made pcl_for_each_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. xdr_check_reply_chunk() funnels Reply chunks through xdr_check_write_chunk() and inherits the same rejection. pcl_alloc_write() 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 list_add_tail() follows the segment fill loop, ensuring only fully-populated chunks appear on the list. Fixes: 78147ca8b4a9 ("svcrdma: Add a "parsed chunk list" data structure") Cc: stable@vger.kernel.org Assisted-by: kres (claude-opus-4-7) Signed-off-by: Chris Mason Acked-by: Jeff Layton Link: https://patch.msgid.link/20260526-rpc-kernel-bugs-v1-5-e251306ccca9@oracle.com Signed-off-by: Chuck Lever Signed-off-by: Sasha Levin --- net/sunrpc/xprtrdma/svc_rdma_pcl.c | 2 +- net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 9 ++++++--- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/net/sunrpc/xprtrdma/svc_rdma_pcl.c b/net/sunrpc/xprtrdma/svc_rdma_pcl.c index b63cfeaa29234..a1c61311714da 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_pcl.c +++ b/net/sunrpc/xprtrdma/svc_rdma_pcl.c @@ -213,7 +213,6 @@ bool pcl_alloc_write(struct svc_rdma_recv_ctxt *rctxt, chunk = pcl_alloc_chunk(segcount, 0); if (!chunk) return false; - list_add_tail(&chunk->ch_list, &pcl->cl_chunks); for (j = 0; j < segcount; j++) { segment = &chunk->ch_segments[j]; @@ -225,6 +224,7 @@ bool pcl_alloc_write(struct svc_rdma_recv_ctxt *rctxt, chunk->ch_length += segment->rs_length; chunk->ch_segcount++; } + list_add_tail(&chunk->ch_list, &pcl->cl_chunks); } return true; } diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c index 9d60faf3de45d..0cdef62a160f9 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c @@ -487,10 +487,13 @@ static bool xdr_check_write_chunk(struct svc_rdma_recv_ctxt *rctxt) return false; /* Before trusting the segcount value enough to use it in - * a computation, perform a simple range check. This is an - * arbitrary but sensible limit (ie, not architectural). + * a computation, perform a simple range check. A zero + * segcount describes no remote buffer and is rejected so + * downstream consumers never see a degenerate ch_segcount==0 + * chunk. The upper bound is an arbitrary but sensible limit + * (ie, not architectural). */ - if (unlikely(segcount > RPCSVC_MAXPAGES)) + if (segcount == 0 || unlikely(segcount > RPCSVC_MAXPAGES)) return false; p = xdr_inline_decode(&rctxt->rc_stream, -- 2.53.0