[lttng-dev] [PATCH lttng-ust v2] Fix: fd of an elf object must be registered to the fd tracker

[Jonathan Rajotte]

The open call take place inside ust, it must be tracked to prevent external
closing.

The bug can be hit during tracing of an application for which the probe
provider is loaded using LD_PRELOAD in combination with the fd utility
shared object. The application is responsible for closing all possible fd.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien at efficios.com>
---

v2:
Cleanup error path of lttng_ust_elf_create by using lttng_ust_elf_destroy.
This take care of my previous mistake regarding double locking in the error
path and move the cleanup logic to a single place.

lttng_ust_elf_destroy now handle cases where fd < 0.
---
 liblttng-ust/lttng-ust-elf.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/liblttng-ust/lttng-ust-elf.c b/liblttng-ust/lttng-ust-elf.c
index a496841a..f2c09829 100644
--- a/liblttng-ust/lttng-ust-elf.c
+++ b/liblttng-ust/lttng-ust-elf.c
@@ -27,6 +27,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <stdbool.h>
+#include <ust-fd.h>
 #include "lttng-tracer-core.h"
 
 #define BUF_LEN	4096
@@ -248,15 +249,20 @@ struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 		goto error;
 	}
 
+
 	elf->path = strdup(path);
 	if (!elf->path) {
 		goto error;
 	}
 
+	lttng_ust_lock_fd_tracker();
 	elf->fd = open(elf->path, O_RDONLY | O_CLOEXEC);
 	if (elf->fd < 0) {
+		lttng_ust_unlock_fd_tracker();
 		goto error;
 	}
+	lttng_ust_add_fd_to_tracker(elf->fd);
+	lttng_ust_unlock_fd_tracker();
 
 	if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
 		goto error;
@@ -309,16 +315,7 @@ struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 	return elf;
 
 error:
-	if (elf) {
-		free(elf->ehdr);
-		if (elf->fd >= 0) {
-			if (close(elf->fd)) {
-				abort();
-			}
-		}
-		free(elf->path);
-		free(elf);
-	}
+	lttng_ust_elf_destroy(elf);
 	return NULL;
 }
 
@@ -339,14 +336,25 @@ uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
  */
 void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
 {
+	int ret;
+
 	if (!elf) {
 		return;
 	}
 
-	free(elf->ehdr);
-	if (close(elf->fd)) {
-		abort();
+	if (elf->fd >= 0) {
+		lttng_ust_lock_fd_tracker();
+		ret = close(elf->fd);
+		if (!ret) {
+			lttng_ust_delete_fd_from_tracker(elf->fd);
+		} else {
+			PERROR("close");
+			abort();
+		}
+		lttng_ust_unlock_fd_tracker();
 	}
+
+	free(elf->ehdr);
 	free(elf->path);
 	free(elf);
 }
-- 
2.11.0