sunrpc: harden rq_procinfo lifecycle to prevent double-free

The svc_release_rqst() function executes the callback inside
rqstp->rq_procinfo->pc_release. However, if a worker thread begins
processing a new request and encounters an early error path (e.g.,
unsupported protocol, short frame, or bad auth) before a valid
rq_procinfo is installed, a stale release hook can be re-triggered
against reused state from the previous RPC, resulting in a double-free
or use-after-free vulnerability.

Harden the lifecycle of rq_procinfo by:
1. Ensuring svc_release_rqst() always clears rq_procinfo after the
   optional pc_release() call, regardless of whether the hook exists.
2. Explicitly clearing rq_procinfo at request entry in svc_process()
   before any early decode or drop paths.
3. Ensuring svc_process_bc() does the same at backchannel entry.

This guarantees that error flows will not encounter a non-NULL stale
rq_procinfo pointer when there is nothing to release.

Fixes: d9adbb6e10bf ("sunrpc: delay pc_release callback until after the reply is sent")
Cc: stable@vger.kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Suggested-by: Chuck Lever <cel@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Luxiao Xu <rakukuip@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 576fa42e7abf..ae9ec4bf34f7 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1598,6 +1598,12 @@ static void svc_release_rqst(struct svc_rqst *rqstp)
 
 	if (procp && procp->pc_release)
 		procp->pc_release(rqstp);
+
+	/*
+	 * A subsequent svc_release_rqst() on this rqstp must not
+	 * re-invoke pc_release against released state.
+	 */
+	rqstp->rq_procinfo = NULL;
 }
 
 /**
@@ -1616,6 +1622,9 @@ void svc_process(struct svc_rqst *rqstp)
 		svc_xprt_deferred_close(rqstp->rq_xprt);
 #endif
 
+	/* Discard a stale release hook from a previous RPC. */
+	rqstp->rq_procinfo = NULL;
+
 	/*
 	 * Setup response xdr_buf.
 	 * Initially it has just one page
@@ -1672,6 +1681,7 @@ void svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp)
 	int proc_error;
 
 	/* Build the svc_rqst used by the common processing routine */
+	rqstp->rq_procinfo = NULL;
 	rqstp->rq_xid = req->rq_xid;
 	rqstp->rq_prot = req->rq_xprt->prot;
 	rqstp->rq_bc_net = req->rq_xprt->xprt_net;