Fix: event-expr.c: use-after-free and NULL ptr deref in error path

use-after-free
==============
The following functions are affected:
  `lttng_event_expr_app_specific_context_field_create()`, and
  `lttng_event_expr_array_field_element_create()`.

In one error path we call `lttng_event_expr_destroy()` with the
`&expr->parent` pointer (which is dynamically allocated) and this
function then calls free() on that pointer. Right after that function
call we return the pointer that was just freed.

Fix that by adding a `ret_parent_expr` pointer that is set to NULL on
the error path;

Null pointer dereference
========================
The following functions are affected:
  `lttng_event_expr_app_specific_context_field_create()`,
  `lttng_event_expr_array_field_element_create()`, and
  `create_field_event_expr()`.

We dereference a NULL pointer if the argument sanity check fails.

Fix that by checking if `expr` is non-null before dereferencing it.

Found with scan-build.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I5fdde462d7345d0dae7ecd2e4f46473a92cd11a9

diff --git a/src/lib/lttng-ctl/event-expr.c b/src/lib/lttng-ctl/event-expr.c
index 273866ca389e4bec322ddbfdd6d67a41fc643d1e..126f0ca34bb2246ad29d4cf400c2e4bb547d959e 100644 (file)
--- a/src/lib/lttng-ctl/event-expr.c
+++ b/src/lib/lttng-ctl/event-expr.c
@@ -73,7 +73,10 @@ struct lttng_event_expr_field *create_field_event_expr(
        goto end;
 
 error:
-       lttng_event_expr_destroy(&expr->parent);
+       if (expr) {
+               lttng_event_expr_destroy(&expr->parent);
+       }
+       expr = NULL;
 
 end:
        return expr;
@@ -117,6 +120,7 @@ struct lttng_event_expr *lttng_event_expr_app_specific_context_field_create(
                const char *provider_name, const char *type_name)
 {
        struct lttng_event_expr_app_specific_context_field *expr = NULL;
+       struct lttng_event_expr *ret_parent_expr;
 
        if (!type_name || !provider_name) {
                goto error;
@@ -141,13 +145,17 @@ struct lttng_event_expr *lttng_event_expr_app_specific_context_field_create(
                goto error;
        }
 
+       ret_parent_expr = &expr->parent;
        goto end;
 
 error:
-       lttng_event_expr_destroy(&expr->parent);
+       if (expr) {
+               lttng_event_expr_destroy(&expr->parent);
+       }
+       ret_parent_expr = NULL;
 
 end:
-       return &expr->parent;
+       return ret_parent_expr;
 }
 
 struct lttng_event_expr *lttng_event_expr_array_field_element_create(
@@ -155,6 +163,7 @@ struct lttng_event_expr *lttng_event_expr_array_field_element_create(
                unsigned int index)
 {
        struct lttng_event_expr_array_field_element *expr = NULL;
+       struct lttng_event_expr *ret_parent_expr;
 
        /* The parent array field expression must be an l-value */
        if (!array_field_expr ||
@@ -173,13 +182,17 @@ struct lttng_event_expr *lttng_event_expr_array_field_element_create(
 
        expr->array_field_expr = array_field_expr;
        expr->index = index;
+       ret_parent_expr = &expr->parent;
        goto end;
 
 error:
-       lttng_event_expr_destroy(&expr->parent);
+       if (expr) {
+               lttng_event_expr_destroy(&expr->parent);
+       }
+       ret_parent_expr = NULL;
 
 end:
-       return &expr->parent;
+       return ret_parent_expr;
 }
 
 const char *lttng_event_expr_event_payload_field_get_name(