FAILED: patch "[PATCH] svcrdma: Reject Read lists that exceed the page budget" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 0ca487abb3bdf581851664b5db21f364caf57682
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090330-audacity-nutcase-5491@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0ca487abb3bdf581851664b5db21f364caf57682 Mon Sep 17 00:00:00 2001
From: Chuck Lever <[email protected]>
Date: Tue, 26 May 2026 13:34:54 -0400
Subject: [PATCH] svcrdma: Reject Read lists that exceed the page budget

Individual Read segment lengths are validated at decode time, but nothing prevents a requester from sending multiple segments whose cumulative length exceeds the rq_pages array budget. When one segment fills the page array exactly, the runtime guard in svc_rdma_build_read_segment() is bypassed because len reaches zero. A subsequent segment then accesses the NULL sentinel slot at rq_pages[rq_maxpages], resulting in a NULL pointer dereference during DMA mapping.

Accumulate pages across all Read segments and reject the message at decode time when the total would overflow the page budget.

index d64b5f78ce8a..fdfed1be97da 100644
@@ -440,11 +440,14 @@ static void svc_rdma_build_arg_xdr(struct svc_rqst *rqstp,
  *	    to the first byte past the Read list. rc_read_pcl and
  *	    rc_call_pcl cl_count fields are set to the number of
  *	    Read segments in the list.
- *  %false: Read list is corrupt. @rctxt's xdr_stream is left in an
- *	    unknown state.
+ *  %false: Read list is corrupt or exceeds the page budget. @rctxt's
+ *	    xdr_stream is left in an unknown state.
  */
 static bool xdr_count_read_segments(struct svc_rdma_recv_ctxt *rctxt, __be32 *p)
 {
+	unsigned int maxlen = rctxt->rc_maxpages << PAGE_SHIFT;
+	unsigned int total_len = 0;
+
 	rctxt->rc_call_pcl.cl_count = 0;
 	rctxt->rc_read_pcl.cl_count = 0;
 	while (xdr_item_is_present(p)) {

@@ -458,7 +461,10 @@ static bool xdr_count_read_segments(struct svc_rdma_recv_ctxt *rctxt, __be32 *p)
 
 		xdr_decode_read_segment(p, &position, &handle,
 					    &length, &offset);
-		if (length > rctxt->rc_maxpages << PAGE_SHIFT)
+		if (length > maxlen)
+			return false;
+		total_len += length;
+		if (PAGE_ALIGN(total_len) > maxlen)
 			return false;
 		if (position) {
 			if (position & 3)

From: Chuck Lever <[email protected]>

[ Upstream commit af6f0e06bed818ee7fc8b869915964410020a1c5 ]

The RPC/RDMA Read list decoder stores wire-supplied segment lengths without validation. xdr_count_read_segments() checks 4-byte alignment for non-zero position values but does not cap the segment length.

An oversized rs_length reaches svc_rdma_build_read_segment(), which derives nr_bvec from it and can drive a large dynamic bvec allocation before verifying that enough rq_pages remain. If the post-allocation page-overrun guard fires, the freshly acquired rw context is not returned, leaking the resource.

Reject any segment whose length exceeds the receive context's page budget during Read list decoding, consistent with how xdr_check_write_chunk() bounds Write segment counts against rc_maxpages. Also return the rw context on the existing post-allocation overrun path in svc_rdma_build_read_segment(), keeping that defensive guard balanced.

Stable-dep-of: 0ca487abb3bd ("svcrdma: Reject Read lists that exceed the page budget")

---
 net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 2 ++
 net/sunrpc/xprtrdma/svc_rdma_rw.c       | 5 +++--
 2 files changed, 5 insertions(+), 2 deletions(-)

index 68a0aa627455d..30157636288eb 100644
@@ -448,6 +448,8 @@ static bool xdr_count_read_segments(struct svc_rdma_recv_ctxt *rctxt, __be32 *p)
 
 		xdr_decode_read_segment(p, &position, &handle,
 					    &length, &offset);
+		if (length > rctxt->rc_maxpages << PAGE_SHIFT)
+			return false;
 		if (position) {
 			if (position & 3)
 				return false;

index b3700c1478ea8..626e79a317678 100644
@@ -766,7 +766,7 @@ static int svc_rdma_build_read_segment(struct svc_rqst *rqstp,
 		len -= seg_len;
 
 		if (len && ((head->rc_curpage + 1) > rqstp->rq_maxpages))
-			goto out_overrun;
+			goto out_put;
 	}
 
 	ret = svc_rdma_rw_ctx_init(rdma, ctxt, segment->rs_offset,

@@ -779,7 +779,8 @@ static int svc_rdma_build_read_segment(struct svc_rqst *rqstp,
 	cc->cc_sqecount += ret;
 	return 0;
 
-out_overrun:
+out_put:
+	svc_rdma_put_rw_ctxt(rdma, ctxt);
 	trace_svcrdma_page_overrun_err(&cc->cc_cid, head->rc_curpage);
 	return -EINVAL;
 }

2.53.0

From: Chuck Lever <[email protected]>

[ Upstream commit 0ca487abb3bdf581851664b5db21f364caf57682 ]

Individual Read segment lengths are validated at decode time, but nothing prevents a requester from sending multiple segments whose cumulative length exceeds the rq_pages array budget. When one segment fills the page array exactly, the runtime guard in svc_rdma_build_read_segment() is bypassed because len reaches zero. A subsequent segment then accesses the NULL sentinel slot at rq_pages[rq_maxpages], resulting in a NULL pointer dereference during DMA mapping.

Accumulate pages across all Read segments and reject the message at decode time when the total would overflow the page budget.

---
 net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

index 30157636288eb..1075bfd9fed61 100644
@@ -430,11 +430,14 @@ static void svc_rdma_build_arg_xdr(struct svc_rqst *rqstp,
  *	    to the first byte past the Read list. rc_read_pcl and
  *	    rc_call_pcl cl_count fields are set to the number of
  *	    Read segments in the list.
- *  %false: Read list is corrupt. @rctxt's xdr_stream is left in an
- *	    unknown state.
+ *  %false: Read list is corrupt or exceeds the page budget. @rctxt's
+ *	    xdr_stream is left in an unknown state.
  */
 static bool xdr_count_read_segments(struct svc_rdma_recv_ctxt *rctxt, __be32 *p)
 {
+	unsigned int maxlen = rctxt->rc_maxpages << PAGE_SHIFT;
+	unsigned int total_len = 0;
+
 	rctxt->rc_call_pcl.cl_count = 0;
 	rctxt->rc_read_pcl.cl_count = 0;
 	while (xdr_item_is_present(p)) {

@@ -448,7 +451,10 @@ static bool xdr_count_read_segments(struct svc_rdma_recv_ctxt *rctxt, __be32 *p)
 
 		xdr_decode_read_segment(p, &position, &handle,
 					    &length, &offset);
-		if (length > rctxt->rc_maxpages << PAGE_SHIFT)
+		if (length > maxlen)
+			return false;
+		total_len += length;
+		if (PAGE_ALIGN(total_len) > maxlen)
 			return false;
 		if (position) {
 			if (position & 3)

2.53.0