GCC 7.1 fixes

GCC 7.1 with will warn when we're not checking the snprintf()
return code in cases where the buffer could be truncated. This
patch either checks the snprintf return code (where applicable),
or simply disables the warnings (ztest.c).

Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #6253

cmd/ztest/Makefile.am

@@ -1,6 +1,8 @@
 include $(top_srcdir)/config/Rules.am
 
-AM_CFLAGS += $(DEBUG_STACKFLAGS) $(FRAME_LARGER_THAN)
+# -Wnoformat-truncation to get rid of compiler warning for unchecked
+#  truncating snprintfs on gcc 7.1.1.
+AM_CFLAGS += $(DEBUG_STACKFLAGS) $(FRAME_LARGER_THAN) $(NO_FORMAT_TRUNCATION)
 AM_CPPFLAGS += -DDEBUG
 
 DEFAULT_INCLUDES += \

config/user-no-format-truncation.m4

@@ -0,0 +1,22 @@
+dnl #
+dnl # Check if gcc supports -Wno-format-truncation option.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_USER_NO_FORMAT_TRUNCATION], [
+	AC_MSG_CHECKING([for -Wno-format-truncation support])
+
+	saved_flags="$CFLAGS"
+	CFLAGS="$CFLAGS -Wno-format-truncation"
+
+	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [])],
+	[
+		NO_FORMAT_TRUNCATION=-Wno-format-truncation
+		AC_MSG_RESULT([yes])
+	],
+	[
+		NO_FORMAT_TRUNCATION=
+		AC_MSG_RESULT([no])
+	])
+
+	CFLAGS="$saved_flags"
+	AC_SUBST([NO_FORMAT_TRUNCATION])
+])

config/user.m4

@@ -17,6 +17,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_RUNSTATEDIR
 	ZFS_AC_CONFIG_USER_MAKEDEV_IN_SYSMACROS
 	ZFS_AC_CONFIG_USER_MAKEDEV_IN_MKDEV
+	ZFS_AC_CONFIG_USER_NO_FORMAT_TRUNCATION
 
 	ZFS_AC_TEST_FRAMEWORK
 

lib/libspl/include/assert.h

@@ -40,6 +40,20 @@ libspl_assert(const char *buf, const char *file, const char *func, int line)
 	abort();
 }
 
+/* printf version of libspl_assert */
+static inline void
+libspl_assertf(const char *file, const char *func, int line, char *format, ...)
+{
+	va_list args;
+
+	va_start(args, format);
+	vfprintf(stderr, format, args);
+	fprintf(stderr, "\n");
+	fprintf(stderr, "ASSERT at %s:%d:%s()", file, line, func);
+	va_end(args);
+	abort();
+}
+
 #ifdef verify
 #undef verify
 #endif
@@ -55,13 +69,9 @@ libspl_assert(const char *buf, const char *file, const char *func, int line)
 do {									\
 	const TYPE __left = (TYPE)(LEFT);				\
 	const TYPE __right = (TYPE)(RIGHT);				\
-	if (!(__left OP __right)) {					\
+	if (!(__left OP __right))					\
-		char *__buf = alloca(256);				\
+		libspl_assertf(__FILE__, __FUNCTION__, __LINE__,	\
-		(void) snprintf(__buf, 256,				\
+		    "%s %s %s (0x%llx %s 0x%llx)", #LEFT, #OP, #RIGHT);	\
-		    "%s %s %s (0x%llx %s 0x%llx)", #LEFT, #OP, #RIGHT,	\
-		    (u_longlong_t)__left, #OP, (u_longlong_t)__right);	\
-		libspl_assert(__buf, __FILE__, __FUNCTION__, __LINE__);	\
-	}								\
 } while (0)
 
 #define	VERIFY3S(x, y, z)	VERIFY3_IMPL(x, y, z, int64_t)

lib/libzfs/libzfs_dataset.c

@@ -3567,8 +3567,9 @@ zfs_check_snap_cb(zfs_handle_t *zhp, void *arg)
 	char name[ZFS_MAX_DATASET_NAME_LEN];
 	int rv = 0;
 
-	(void) snprintf(name, sizeof (name),
+	if (snprintf(name, sizeof (name), "%s@%s", zhp->zfs_name,
-	    "%s@%s", zhp->zfs_name, dd->snapname);
+	    dd->snapname) >= sizeof (name))
+		return (EINVAL);
 
 	if (lzc_exists(name))
 		verify(nvlist_add_boolean(dd->nvl, name) == 0);
@@ -3782,8 +3783,9 @@ zfs_snapshot_cb(zfs_handle_t *zhp, void *arg)
 	int rv = 0;
 
 	if (zfs_prop_get_int(zhp, ZFS_PROP_INCONSISTENT) == 0) {
-		(void) snprintf(name, sizeof (name),
+		if (snprintf(name, sizeof (name), "%s@%s", zfs_get_name(zhp),
-		    "%s@%s", zfs_get_name(zhp), sd->sd_snapname);
+		    sd->sd_snapname) >= sizeof (name))
+			return (EINVAL);
 
 		fnvlist_add_boolean(sd->sd_nvl, name);
 
@@ -4527,8 +4529,9 @@ zfs_hold_one(zfs_handle_t *zhp, void *arg)
 	char name[ZFS_MAX_DATASET_NAME_LEN];
 	int rv = 0;
 
-	(void) snprintf(name, sizeof (name),
+	if (snprintf(name, sizeof (name), "%s@%s", zhp->zfs_name,
-	    "%s@%s", zhp->zfs_name, ha->snapname);
+	    ha->snapname) >= sizeof (name))
+		return (EINVAL);
 
 	if (lzc_exists(name))
 		fnvlist_add_string(ha->nvl, name, ha->tag);
@@ -4647,8 +4650,11 @@ zfs_release_one(zfs_handle_t *zhp, void *arg)
 	int rv = 0;
 	nvlist_t *existing_holds;
 
-	(void) snprintf(name, sizeof (name),
+	if (snprintf(name, sizeof (name), "%s@%s", zhp->zfs_name,
-	    "%s@%s", zhp->zfs_name, ha->snapname);
+	    ha->snapname) >= sizeof (name)) {
+		ha->error = EINVAL;
+		rv = EINVAL;
+	}
 
 	if (lzc_get_holds(name, &existing_holds) != 0) {
 		ha->error = ENOENT;

lib/libzfs/libzfs_iter.c

@@ -204,8 +204,11 @@ zfs_iter_bookmarks(zfs_handle_t *zhp, zfs_iter_f func, void *data)
 		bmark_name = nvpair_name(pair);
 		bmark_props = fnvpair_value_nvlist(pair);
 
-		(void) snprintf(name, sizeof (name), "%s#%s", zhp->zfs_name,
+		if (snprintf(name, sizeof (name), "%s#%s", zhp->zfs_name,
-		    bmark_name);
+		    bmark_name) >= sizeof (name)) {
+			err = EINVAL;
+			goto out;
+		}
 
 		nzhp = make_bookmark_handle(zhp, name, bmark_props);
 		if (nzhp == NULL)

lib/libzfs/libzfs_sendrecv.c

@@ -1867,9 +1867,13 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 			    drr_versioninfo, DMU_COMPOUNDSTREAM);
 			DMU_SET_FEATUREFLAGS(drr.drr_u.drr_begin.
 			    drr_versioninfo, featureflags);
-			(void) snprintf(drr.drr_u.drr_begin.drr_toname,
+			if (snprintf(drr.drr_u.drr_begin.drr_toname,
 			    sizeof (drr.drr_u.drr_begin.drr_toname),
-			    "%s@%s", zhp->zfs_name, tosnap);
+			    "%s@%s", zhp->zfs_name, tosnap) >=
+			    sizeof (drr.drr_u.drr_begin.drr_toname)) {
+				err = EINVAL;
+				goto stderr_out;
+			}
 			drr.drr_payloadlen = buflen;
 
 			err = dump_record(&drr, packbuf, buflen, &zc, outfd);

module/zfs/zfs_ioctl.c

@@ -3628,8 +3628,10 @@ zfs_ioc_destroy(zfs_cmd_t *zc)
 			 */
 			char namebuf[ZFS_MAX_DATASET_NAME_LEN + 6];
 
-			(void) snprintf(namebuf, sizeof (namebuf),
+			if (snprintf(namebuf, sizeof (namebuf), "%s/%s",
-			    "%s/%s", zc->zc_name, recv_clone_name);
+			    zc->zc_name, recv_clone_name) >=
+			    sizeof (namebuf))
+				return (SET_ERROR(EINVAL));
 
 			/*
 			 * Try to remove the hidden child (%recv) and after

module/zfs/zvol.c

@@ -2154,14 +2154,12 @@ zvol_rename_minors_impl(const char *oldname, const char *newname)
 {
 	zvol_state_t *zv, *zv_next;
 	int oldnamelen, newnamelen;
-	char *name;
 
 	if (zvol_inhibit_dev)
 		return;
 
 	oldnamelen = strlen(oldname);
 	newnamelen = strlen(newname);
-	name = kmem_alloc(MAXNAMELEN, KM_SLEEP);
 
 	mutex_enter(&zvol_state_lock);
 
@@ -2181,18 +2179,17 @@ zvol_rename_minors_impl(const char *oldname, const char *newname)
 		} else if (strncmp(zv->zv_name, oldname, oldnamelen) == 0 &&
 		    (zv->zv_name[oldnamelen] == '/' ||
 		    zv->zv_name[oldnamelen] == '@')) {
-			snprintf(name, MAXNAMELEN, "%s%c%s", newname,
+			char *name = kmem_asprintf("%s%c%s", newname,
 			    zv->zv_name[oldnamelen],
 			    zv->zv_name + oldnamelen + 1);
 			zvol_rename_minor(zv, name);
+			kmem_free(name, strlen(name + 1));
 		}
 
 		mutex_exit(&zv->zv_state_lock);
 	}
 
 	mutex_exit(&zvol_state_lock);
-
-	kmem_free(name, MAXNAMELEN);
 }
 
 typedef struct zvol_snapdev_cb_arg {