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Subject: [PATCH 1/2] fsidd: don't use assert() on expr with side-effect.
From:   NeilBrown <neilb@suse.de>
To:     Steve Dickson <steved@redhat.com>,
        Richard Weinberger <richard@nod.at>
Cc:     linux-nfs@vger.kernel.org
Date:   Mon, 08 May 2023 16:19:11 +1000
Message-ID: <168352675193.17279.3466985331128410653.stgit@noble.brown>
In-Reply-To: <168352657591.17279.393573102599959056.stgit@noble.brown>
References: <168352657591.17279.393573102599959056.stgit@noble.brown>
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assert() is not guaranteed to evaluate its arg.  When compiled with
-DNDEBUG, the evaluation is skipped.  We don't currently compile with
-DNDEBUG, but relying on that is poor form, particularly as this is
described as "sample code" in the git log.

So introduce assert_safe() and use that when there are side-effects.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 support/reexport/fsidd.c |   28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/support/reexport/fsidd.c b/support/reexport/fsidd.c
index 410b3a370d6d..3fef1ef3512b 100644
--- a/support/reexport/fsidd.c
+++ b/support/reexport/fsidd.c
@@ -26,6 +26,11 @@
 static struct event_base *evbase;
 static struct reexpdb_backend_plugin *dbbackend = &sqlite_plug_ops;
 
+/* assert_safe() always evalutes it argument, as it might have
+ * a side-effect.  assert() won't if compiled with NDEBUG
+ */
+#define assert_safe(__sideeffect) (__sideeffect ? 0 : ({assert(0) ; 0;}))
+
 static void client_cb(evutil_socket_t cl, short ev, void *d)
 {
 	struct event *me = d;
@@ -56,12 +61,11 @@ static void client_cb(evutil_socket_t cl, short ev, void *d)
 
 		if (dbbackend->fsidnum_by_path(req_path, &fsidnum, false, &found)) {
 			if (found)
-				assert(asprintf(&answer, "+ %u", fsidnum) != -1);
+				assert_safe(asprintf(&answer, "+ %u", fsidnum) != -1);
 			else
-				assert(asprintf(&answer, "+ ") != -1);
-		
+				assert_safe(asprintf(&answer, "+ ") != -1);
 		} else {
-			assert(asprintf(&answer, "- %s", "Command failed") != -1);
+			assert_safe(asprintf(&answer, "- %s", "Command failed") != -1);
 		}
 
 		(void)send(cl, answer, strlen(answer), 0);
@@ -78,13 +82,13 @@ static void client_cb(evutil_socket_t cl, short ev, void *d)
 
 		if (dbbackend->fsidnum_by_path(req_path, &fsidnum, true, &found)) {
 			if (found) {
-				assert(asprintf(&answer, "+ %u", fsidnum) != -1);
+				assert_safe(asprintf(&answer, "+ %u", fsidnum) != -1);
 			} else {
-				assert(asprintf(&answer, "+ ") != -1);
+				assert_safe(asprintf(&answer, "+ ") != -1);
 			}
 		
 		} else {
-			assert(asprintf(&answer, "- %s", "Command failed") != -1);
+			assert_safe(asprintf(&answer, "- %s", "Command failed") != -1);
 		}
 
 		(void)send(cl, answer, strlen(answer), 0);
@@ -106,15 +110,15 @@ static void client_cb(evutil_socket_t cl, short ev, void *d)
 		}
 
 		if (bad_input) {
-			assert(asprintf(&answer, "- %s", "Command failed: Bad input") != -1);
+			assert_safe(asprintf(&answer, "- %s", "Command failed: Bad input") != -1);
 		} else {
 			if (dbbackend->path_by_fsidnum(fsidnum, &path, &found)) {
 				if (found)
-					assert(asprintf(&answer, "+ %s", path) != -1);
+					assert_safe(asprintf(&answer, "+ %s", path) != -1);
 				else
-					assert(asprintf(&answer, "+ ") != -1);
+					assert_safe(asprintf(&answer, "+ ") != -1);
 			} else {
-				assert(asprintf(&answer, "+ ") != -1);
+				assert_safe(asprintf(&answer, "+ ") != -1);
 			}
 		}
 
@@ -129,7 +133,7 @@ static void client_cb(evutil_socket_t cl, short ev, void *d)
 	} else {
 		char *answer = NULL;
 
-		assert(asprintf(&answer, "- bad command") != -1);
+		assert_safe(asprintf(&answer, "- bad command") != -1);
 		(void)send(cl, answer, strlen(answer), 0);
 
 		free(answer);