[PATCH] nfsd: use dynamic allocation for oversized NFSv4.0 replay cache

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

Commit 1e8e9913672a ("nfsd: fix heap overflow in NFSv4.0 LOCK
replay cache") capped the replay cache copy at NFSD4_REPLAY_ISIZE
to prevent a heap overflow, but set rp_buflen to zero when the
encoded response exceeded the inline buffer. A retransmitted LOCK
reaching the replay path then produced only a status code with no
operation body, resulting in a malformed XDR response.

When the encoded response exceeds the 112-byte inline rp_ibuf, a
buffer is kmalloc'd to hold it. If the allocation fails, rp_buflen
remains zero, preserving the behavior from the capped-copy fix.
The buffer is freed when the stateowner is released or when a
subsequent operation's response fits in the inline buffer.

Fixes: 1e8e9913672a ("nfsd: fix heap overflow in NFSv4.0 LOCK replay cache")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4state.c | 16 ++++++++++++++++
 fs/nfsd/nfs4xdr.c   | 23 ++++++++++++++++-------
 fs/nfsd/state.h     | 12 +++++++-----
 3 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index ba49f49bb93b..b4d0e82b2690 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1496,8 +1496,24 @@ release_all_access(struct nfs4_ol_stateid *stp)
 	}
 }
 
+/**
+ * nfs4_replay_free_cache - release dynamically allocated replay buffer
+ * @rp: replay cache to reset
+ *
+ * If @rp->rp_buf points to a kmalloc'd buffer, free it and reset
+ * rp_buf to the inline rp_ibuf. Always zeroes rp_buflen.
+ */
+void nfs4_replay_free_cache(struct nfs4_replay *rp)
+{
+	if (rp->rp_buf != rp->rp_ibuf)
+		kfree(rp->rp_buf);
+	rp->rp_buf = rp->rp_ibuf;
+	rp->rp_buflen = 0;
+}
+
 static inline void nfs4_free_stateowner(struct nfs4_stateowner *sop)
 {
+	nfs4_replay_free_cache(&sop->so_replay);
 	kfree(sop->so_owner.data);
 	sop->so_ops->so_free(sop);
 }
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 690f7a3122ec..2a0946c630e1 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -6282,14 +6282,23 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op)
 		int len = xdr->buf->len - (op_status_offset + XDR_UNIT);
 
 		so->so_replay.rp_status = op->status;
-		if (len <= NFSD4_REPLAY_ISIZE) {
-			so->so_replay.rp_buflen = len;
-			read_bytes_from_xdr_buf(xdr->buf,
-						op_status_offset + XDR_UNIT,
-						so->so_replay.rp_buf, len);
-		} else {
-			so->so_replay.rp_buflen = 0;
+		if (len > NFSD4_REPLAY_ISIZE) {
+			char *buf = kmalloc(len, GFP_KERNEL);
+
+			nfs4_replay_free_cache(&so->so_replay);
+			if (buf) {
+				so->so_replay.rp_buf = buf;
+			} else {
+				/* rp_buflen already zeroed; skip caching */
+				goto status;
+			}
+		} else if (so->so_replay.rp_buf != so->so_replay.rp_ibuf) {
+			nfs4_replay_free_cache(&so->so_replay);
 		}
+		so->so_replay.rp_buflen = len;
+		read_bytes_from_xdr_buf(xdr->buf,
+					op_status_offset + XDR_UNIT,
+					so->so_replay.rp_buf, len);
 	}
 status:
 	op->status = nfsd4_map_status(op->status,
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 3159c7b67f50..9b05462da4cc 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -554,10 +554,10 @@ struct nfs4_client_reclaim {
  *   ~32(deleg. ace) = 112 bytes
  *
  * Some responses can exceed this. A LOCK denial includes the conflicting
- * lock owner, which can be up to 1024 bytes (NFS4_OPAQUE_LIMIT). Responses
- * larger than REPLAY_ISIZE are not cached in rp_ibuf; only rp_status is
- * saved. Enlarging this constant increases the size of every
- * nfs4_stateowner.
+ * lock owner, which can be up to 1024 bytes (NFS4_OPAQUE_LIMIT). When a
+ * response exceeds REPLAY_ISIZE, a buffer is dynamically allocated. If
+ * that allocation fails, only rp_status is saved. Enlarging this constant
+ * increases the size of every nfs4_stateowner.
  */
 
 #define NFSD4_REPLAY_ISIZE       112 
@@ -569,12 +569,14 @@ struct nfs4_client_reclaim {
 struct nfs4_replay {
 	__be32			rp_status;
 	unsigned int		rp_buflen;
-	char			*rp_buf;
+	char			*rp_buf; /* rp_ibuf or kmalloc'd */
 	struct knfsd_fh		rp_openfh;
 	int			rp_locked;
 	char			rp_ibuf[NFSD4_REPLAY_ISIZE];
 };
 
+extern void nfs4_replay_free_cache(struct nfs4_replay *rp);
+
 struct nfs4_stateowner;
 
 struct nfs4_stateowner_operations {
-- 
2.53.0