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 <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tony Hutter <[email protected]>
Closes #6253 

9 files changed, 74 insertions, 27 deletions

diff --git a/cmd/ztest/Makefile.am b/cmd/ztest/Makefile.am
index a2f3b5a6b..5167d0c1d 100644
--- a/cmd/ztest/Makefile.am
+++ b/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 += \
diff --git a/config/user-no-format-truncation.m4 b/config/user-no-format-truncation.m4
new file mode 100644
index 000000000..4426907ee
--- /dev/null
+++ b/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])
+])
diff --git a/config/user.m4 b/config/user.m4
index 079e2e73b..21ff7143a 100644
--- a/config/user.m4
+++ b/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
 
diff --git a/lib/libspl/include/assert.h b/lib/libspl/include/assert.h
index bd89ad94f..6237d6bcf 100644
--- a/lib/libspl/include/assert.h
+++ b/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)) {					\
-		char *__buf = alloca(256);				\
-		(void) snprintf(__buf, 256,				\
-		    "%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__);	\
-	}								\
+	if (!(__left OP __right))					\
+		libspl_assertf(__FILE__, __FUNCTION__, __LINE__,	\
+		    "%s %s %s (0x%llx %s 0x%llx)", #LEFT, #OP, #RIGHT);	\
 } while (0)
 
 #define	VERIFY3S(x, y, z)	VERIFY3_IMPL(x, y, z, int64_t)
diff --git a/lib/libzfs/libzfs_dataset.c b/lib/libzfs/libzfs_dataset.c
index bc630919a..51c168ad7 100644
--- a/lib/libzfs/libzfs_dataset.c
+++ b/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),
-	    "%s@%s", zhp->zfs_name, dd->snapname);
+	if (snprintf(name, sizeof (name), "%s@%s", zhp->zfs_name,
+	    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),
-		    "%s@%s", zfs_get_name(zhp), sd->sd_snapname);
+		if (snprintf(name, sizeof (name), "%s@%s", zfs_get_name(zhp),
+		    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),
-	    "%s@%s", zhp->zfs_name, ha->snapname);
+	if (snprintf(name, sizeof (name), "%s@%s", zhp->zfs_name,
+	    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),
-	    "%s@%s", zhp->zfs_name, ha->snapname);
+	if (snprintf(name, sizeof (name), "%s@%s", zhp->zfs_name,
+	    ha->snapname) >= sizeof (name)) {
+		ha->error = EINVAL;
+		rv = EINVAL;
+	}
 
 	if (lzc_get_holds(name, &existing_holds) != 0) {
 		ha->error = ENOENT;
diff --git a/lib/libzfs/libzfs_iter.c b/lib/libzfs/libzfs_iter.c
index d78c757a5..57ebdd89d 100644
--- a/lib/libzfs/libzfs_iter.c
+++ b/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,
-		    bmark_name);
+		if (snprintf(name, sizeof (name), "%s#%s", zhp->zfs_name,
+		    bmark_name) >= sizeof (name)) {
+			err = EINVAL;
+			goto out;
+		}
 
 		nzhp = make_bookmark_handle(zhp, name, bmark_props);
 		if (nzhp == NULL)
diff --git a/lib/libzfs/libzfs_sendrecv.c b/lib/libzfs/libzfs_sendrecv.c
index 71ee8faae..ff909f1e3 100644
--- a/lib/libzfs/libzfs_sendrecv.c
+++ b/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);
diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 8cdfe31a2..a2f7f045f 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/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),
-			    "%s/%s", zc->zc_name, recv_clone_name);
+			if (snprintf(namebuf, sizeof (namebuf), "%s/%s",
+			    zc->zc_name, recv_clone_name) >=
+			    sizeof (namebuf))
+				return (SET_ERROR(EINVAL));
 
 			/*
 			 * Try to remove the hidden child (%recv) and after
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 75ed06e03..528acbc22 100644
--- a/module/zfs/zvol.c
+++ b/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 {