[lttng-dev] [PATCH lttng-ust] 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>
---
 liblttng-ust/lttng-ust-elf.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/liblttng-ust/lttng-ust-elf.c b/liblttng-ust/lttng-ust-elf.c
index a496841a..5f3b280e 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
@@ -242,6 +243,8 @@ struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 	uint8_t e_ident[EI_NIDENT];
 	struct lttng_ust_elf_shdr *section_names_shdr;
 	struct lttng_ust_elf *elf = NULL;
+	int fd;
+	int ret;
 
 	elf = zmalloc(sizeof(struct lttng_ust_elf));
 	if (!elf) {
@@ -253,10 +256,16 @@ struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 		goto error;
 	}
 
-	elf->fd = open(elf->path, O_RDONLY | O_CLOEXEC);
-	if (elf->fd < 0) {
+	lttng_ust_lock_fd_tracker();
+	fd = open(elf->path, O_RDONLY | O_CLOEXEC);
+	if (fd < 0) {
+		lttng_ust_unlock_fd_tracker();
 		goto error;
 	}
+	lttng_ust_add_fd_to_tracker(fd);
+	lttng_ust_unlock_fd_tracker();
+
+	elf->fd = fd;
 
 	if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
 		goto error;
@@ -312,9 +321,15 @@ error:
 	if (elf) {
 		free(elf->ehdr);
 		if (elf->fd >= 0) {
-			if (close(elf->fd)) {
+			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_lock_fd_tracker();
 		}
 		free(elf->path);
 		free(elf);
@@ -339,14 +354,23 @@ 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)) {
+	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