trace, tracelog: don't truncate /etc/ld.so.preload

netblue30 · Oct 2, 2021 · 19e1ee0 · 19e1ee0
1 parent 8d36b86
commit 19e1ee0
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Showing 3 changed files with 27 additions and 17 deletions.
diff --git a/src/firejail/firejail.h b/src/firejail/firejail.h
@@ -621,7 +621,8 @@ void caps_print_filter(pid_t pid) __attribute__((noreturn));
 void caps_drop_dac_override(void);
 
 // fs_trace.c
-void fs_trace_preload(void);
+void fs_trace_touch_preload(void);
+void fs_trace_touch_or_store_preload(void);
 void fs_tracefile(void);
 void fs_trace(void);
 

diff --git a/src/firejail/fs_trace.c b/src/firejail/fs_trace.c
@@ -26,19 +26,26 @@
 #include <fcntl.h>
 #include <pwd.h>
 
-void fs_trace_preload(void) {
+// create an empty /etc/ld.so.preload
+void fs_trace_touch_preload(void) {
+	create_empty_file_as_root("/etc/ld.so.preload", S_IRUSR | S_IWRITE | S_IRGRP | S_IROTH);
+}
+
+void fs_trace_touch_or_store_preload(void) {
 	struct stat s;
 
-	// create an empty /etc/ld.so.preload
-	if (stat("/etc/ld.so.preload", &s)) {
-		if (arg_debug)
-			printf("Creating an empty /etc/ld.so.preload file\n");
-		FILE *fp = fopen("/etc/ld.so.preload", "wxe");
-		if (!fp)
-			errExit("fopen");
-		SET_PERMS_STREAM(fp, 0, 0, S_IRUSR | S_IWRITE | S_IRGRP | S_IROTH);
-		fclose(fp);
-		fs_logger("touch /etc/ld.so.preload");
+	if (stat("/etc/ld.so.preload", &s) != 0) {
+		fs_trace_touch_preload();
+		return;
+	}
+
+	if (s.st_size == 0)
+		return;
+
+	// create a copy of /etc/ld.so.preload
+	if (copy_file("/etc/ld.so.preload", RUN_LDPRELOAD_FILE, 0, 0, S_IRUSR | S_IWRITE | S_IRGRP | S_IROTH)) {
+		fprintf(stderr, "Error: cannot copy /etc/ld.so.preload file\n");
+		exit(1);
 	}
 }
 
@@ -83,7 +90,7 @@ void fs_trace(void) {
 	if (arg_debug)
 		printf("Create the new ld.so.preload file\n");
 
-	FILE *fp = fopen(RUN_LDPRELOAD_FILE, "we");
+	FILE *fp = fopen(RUN_LDPRELOAD_FILE, "ae");
 	if (!fp)
 		errExit("fopen");
 	const char *prefix = RUN_FIREJAIL_LIB_DIR;

diff --git a/src/firejail/sandbox.c b/src/firejail/sandbox.c
@@ -798,7 +798,7 @@ int sandbox(void* sandbox_arg) {
 
 	// trace pre-install
 	if (need_preload)
-		fs_trace_preload();
+		fs_trace_touch_or_store_preload();
 
 	// store hosts file
 	if (cfg.hosts_file)
@@ -814,8 +814,10 @@ int sandbox(void* sandbox_arg) {
 		//****************************
 		// trace pre-install, this time inside chroot
 		//****************************
-		if (need_preload)
-			fs_trace_preload();
+		if (need_preload) {
+			unlink(RUN_LDPRELOAD_FILE);
+			fs_trace_touch_or_store_preload();
+		}
 	}
 	else
 #endif
@@ -992,7 +994,7 @@ int sandbox(void* sandbox_arg) {
 
 			// create /etc/ld.so.preload file again
 			if (need_preload)
-				fs_trace_preload();
+				fs_trace_touch_preload();
 
 			// openSUSE configuration is split between /etc and /usr/etc
 			// process private-etc a second time