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From:   Attila Kovacs <attila.kovacs@cfa.harvard.edu>
To:     Libtirpc-devel Mailing List <libtirpc-devel@lists.sourceforge.net>
Cc:     Linux NFS Mailing list <linux-nfs@vger.kernel.org>
Subject: [PATCH 2/2] thread safe clnt destruction.
Date:   Mon, 25 Jul 2022 12:06:46 -0400
Message-Id: <20220725160646.15610-2-attila.kovacs@cfa.harvard.edu>
In-Reply-To: <20220725160646.15610-1-attila.kovacs@cfa.harvard.edu>
References: <20220725160646.15610-1-attila.kovacs@cfa.harvard.edu>
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From: Attila Kovacs <attipaci@gmail.com>

If clnt_dg_destroy() or clnt_vc_destroy() is awoken with other blocked 
operations pending (such as clnt_*_call(), clnt_*_control(), or 
clnt_*_freeres()) but no active operation currently being executed, then the 
client gets destroyed. Then, as the other blocked operations get subsequently 
awoken, they will try operate on an invalid client handle, potentially causing 
unpredictable behavior and stack corruption. 

Signed-off-by: Attila Kovacs <attipaci@gmail.com>
---
 src/clnt_dg.c       | 13 ++++++++++++-
 src/clnt_fd_locks.h |  2 ++
 src/clnt_vc.c       | 13 ++++++++++++-
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/clnt_dg.c b/src/clnt_dg.c
index b2043ac..166af63 100644
--- a/src/clnt_dg.c
+++ b/src/clnt_dg.c
@@ -101,6 +101,7 @@ extern mutex_t clnt_fd_lock;
 #define	release_fd_lock(fd_lock, mask) {	\
 	mutex_lock(&clnt_fd_lock);	\
 	fd_lock->active = FALSE;	\
+	fd_lock->pending--;		\
 	thr_sigsetmask(SIG_SETMASK, &(mask), NULL); \
 	cond_signal(&fd_lock->cv);	\
 	mutex_unlock(&clnt_fd_lock);    \
@@ -311,6 +312,7 @@ clnt_dg_call(cl, proc, xargs, argsp, xresults, resultsp, utimeout)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
+	cu->cu_fd_lock->pending++;
 	while (cu->cu_fd_lock->active)
 		cond_wait(&cu->cu_fd_lock->cv, &clnt_fd_lock);
 	cu->cu_fd_lock->active = TRUE;
@@ -571,10 +573,12 @@ clnt_dg_freeres(cl, xdr_res, res_ptr)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
+	cu->cu_fd_lock->pending++;
 	while (cu->cu_fd_lock->active)
 		cond_wait(&cu->cu_fd_lock->cv, &clnt_fd_lock);
 	xdrs->x_op = XDR_FREE;
 	dummy = (*xdr_res)(xdrs, res_ptr);
+	cu->cu_fd_lock->pending--;
 	thr_sigsetmask(SIG_SETMASK, &mask, NULL);
 	cond_signal(&cu->cu_fd_lock->cv);
 	mutex_unlock(&clnt_fd_lock);
@@ -602,6 +606,7 @@ clnt_dg_control(cl, request, info)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
+	cu->cu_fd_lock->pending++;
 	while (cu->cu_fd_lock->active)
 		cond_wait(&cu->cu_fd_lock->cv, &clnt_fd_lock);
 	cu->cu_fd_lock->active = TRUE;
@@ -742,8 +747,14 @@ clnt_dg_destroy(cl)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
-	while (cu_fd_lock->active)
+	/* wait until all pending operations on client are completed. */
+	while (cu_fd_lock->pending > 0) {
+		/* If a blocked operation can be awakened, then do it. */
+		if (cu_fd_lock->active == FALSE)
+			cond_signal(&cu_fd_lock->cv);
+		/* keep waiting... */
 		cond_wait(&cu_fd_lock->cv, &clnt_fd_lock);
+	}
 	if (cu->cu_closeit)
 		(void)close(cu_fd);
 	XDR_DESTROY(&(cu->cu_outxdrs));
diff --git a/src/clnt_fd_locks.h b/src/clnt_fd_locks.h
index 359f995..6ba62cb 100644
--- a/src/clnt_fd_locks.h
+++ b/src/clnt_fd_locks.h
@@ -50,6 +50,7 @@ static unsigned int fd_locks_prealloc = 0;
 /* per-fd lock */
 struct fd_lock_t {
 	bool_t active;
+	int pending;        /* Number of pending operations on fd */
 	cond_t cv;
 };
 typedef struct fd_lock_t fd_lock_t;
@@ -180,6 +181,7 @@ fd_lock_t* fd_lock_create(int fd, fd_locks_t *fd_locks) {
 		item->fd = fd;
 		item->refs = 1;
 		item->fd_lock.active = FALSE;
+		item->fd_lock.pending = 0;
 		cond_init(&item->fd_lock.cv, 0, (void *) 0);
 		TAILQ_INSERT_HEAD(list, item, link);
 	} else {
diff --git a/src/clnt_vc.c b/src/clnt_vc.c
index 3c73e65..5bbc78b 100644
--- a/src/clnt_vc.c
+++ b/src/clnt_vc.c
@@ -153,6 +153,7 @@ extern mutex_t  clnt_fd_lock;
 #define release_fd_lock(fd_lock, mask) {	\
 	mutex_lock(&clnt_fd_lock);	\
 	fd_lock->active = FALSE;	\
+	fd_lock->pending--;		\
 	thr_sigsetmask(SIG_SETMASK, &(mask), (sigset_t *) NULL);	\
 	cond_signal(&fd_lock->cv);	\
 	mutex_unlock(&clnt_fd_lock);    \
@@ -357,6 +358,7 @@ clnt_vc_call(cl, proc, xdr_args, args_ptr, xdr_results, results_ptr, timeout)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
+	ct->ct_fd_lock->pending++;
 	while (ct->ct_fd_lock->active)
 		cond_wait(&ct->ct_fd_lock->cv, &clnt_fd_lock);
 	ct->ct_fd_lock->active = TRUE;
@@ -495,10 +497,12 @@ clnt_vc_freeres(cl, xdr_res, res_ptr)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
+	ct->ct_fd_lock->pending++;
 	while (ct->ct_fd_lock->active)
 		cond_wait(&ct->ct_fd_lock->cv, &clnt_fd_lock);
 	xdrs->x_op = XDR_FREE;
 	dummy = (*xdr_res)(xdrs, res_ptr);
+	ct->ct_fd_lock->pending--;
 	thr_sigsetmask(SIG_SETMASK, &(mask), NULL);
 	cond_signal(&ct->ct_fd_lock->cv);
 	mutex_unlock(&clnt_fd_lock);
@@ -533,6 +537,7 @@ clnt_vc_control(cl, request, info)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
+	ct->ct_fd_lock->pending++;
 	while (ct->ct_fd_lock->active)
 		cond_wait(&ct->ct_fd_lock->cv, &clnt_fd_lock);
 	ct->ct_fd_lock->active = TRUE;
@@ -655,8 +660,14 @@ clnt_vc_destroy(cl)
 	sigfillset(&newmask);
 	thr_sigsetmask(SIG_SETMASK, &newmask, &mask);
 	mutex_lock(&clnt_fd_lock);
-	while (ct_fd_lock->active)
+	/* wait until all pending operations on client are completed. */
+	while (ct_fd_lock->pending > 0) {
+		/* If a blocked operation can be awakened, then do it. */
+		if (ct_fd_lock->active == FALSE)
+			cond_signal(&ct_fd_lock->cv);
+		/* keep waiting... */
 		cond_wait(&ct_fd_lock->cv, &clnt_fd_lock);
+	}
 	if (ct->ct_closeit && ct->ct_fd != -1) {
 		(void)close(ct->ct_fd);
 	}
-- 
2.37.1