From ce441f065b6eebb166bb006dfd28ea0c6b730384 Mon Sep 17 00:00:00 2001 From: Anton Lindqvist Date: Thu, 3 Sep 2020 22:18:31 +0200 Subject: executor: improve opendir(3) error handling While investigating an OpenBSD reproducer[1][2] I discovered the following: * All threads are stuck on the last `sleep(1000000)` syscall in main(), hence no output for the test machine. * Each executor process created in loop() performs one iteration but exits abnormally during the call to remove_dir(). * Calling remove_dir() will eventually invoke itself recursively since one of the executed syscall is `mkdir("./file0", 0)` meaning that it will try to remove the directory created by execute_one(). However, `opendir(3)` fails with `EACCES` due to the permissions passed to `mkdir(2)` is zero. Instead of exiting, trying to remove the problematic directory in a best effort manner makes the reproducer continue executing the generated syscalls. This work around might be considered to narrow. Another option would be to replace the `sleep(1000000)` with `waitpid(-1, NULL, 0)` until ECHILD is hit. [1] https://syzkaller.appspot.com/bug?id=6f7ce2a0536580a94f65f44e478732ec505e88af [2] https://syzkaller.appspot.com/text?tag=ReproC&x=10fd1a71900000 --- executor/common.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'executor') diff --git a/executor/common.h b/executor/common.h index 81ddefd01..490595ce2 100644 --- a/executor/common.h +++ b/executor/common.h @@ -199,6 +199,7 @@ static void use_temporary_dir(void) #if GOOS_akaros || GOOS_netbsd || GOOS_freebsd || GOOS_openbsd || GOOS_test #if (SYZ_EXECUTOR || SYZ_REPEAT) && SYZ_EXECUTOR_USES_FORK_SERVER && (SYZ_EXECUTOR || SYZ_USE_TMP_DIR) #include +#include #include #include #include @@ -207,8 +208,19 @@ static void use_temporary_dir(void) static void remove_dir(const char* dir) { DIR* dp = opendir(dir); - if (dp == NULL) + if (dp == NULL) { + if (errno == EACCES) { + // We could end up here in a recursive call to remove_dir() below. + // One of executed syscall could end up creating a directory rooted + // in the current working directory created by loop() with zero + // permissions. Try to perform a best effort removal of the + // directory. + if (rmdir(dir)) + exitf("rmdir(%s) failed", dir); + return; + } exitf("opendir(%s) failed", dir); + } struct dirent* ep = 0; while ((ep = readdir(dp))) { if (strcmp(ep->d_name, ".") == 0 || strcmp(ep->d_name, "..") == 0) -- cgit mrf-deployment