Detect a TOCTOU race condition attack on the filesystem by renaming a
file after the seccomp filter evaluation but before the effective
syscall.
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Paul Moore <pmoore@xxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
---
tools/testing/selftests/seccomp/seccomp_bpf.c | 180 +++++++++++++++++++++++++-
1 file changed, 178 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 64b4d758b007..1558e0079fe9 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -10,6 +10,7 @@
#define __have_sigval_t 1
#define __have_sigevent_t 1
+#define _GNU_SOURCE
#include <errno.h>
#include <linux/filter.h>
#include <sys/prctl.h>
@@ -32,8 +33,6 @@
#include <sys/fcntl.h>
#include <sys/mman.h>
#include <sys/times.h>
-
-#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
@@ -2520,6 +2519,183 @@ TEST_F(TRACE_poke_arg_path, argeval_toctou_argument)
EXPECT_EQ(E2BIG, errno);
close(fd);
}
+
+char *new_file(struct __test_metadata *_metadata, const char *name, char buf)
+{
+ int ret, fd, path_len;
+ char *path;
+ const char tmpl[] = "/tmp/seccomp-test_%s.XXXXXX";
+
+ path_len = sizeof(tmpl) - 2 + strlen(name);
+ path = malloc(path_len);
+ ASSERT_NE(path, NULL);
+ ret = snprintf(path, path_len, tmpl, name);
+ ASSERT_EQ(ret, path_len - 1);
+ fd = mkostemp(path, O_CLOEXEC);
+ ASSERT_NE(fd, -1);
+ ret = write(fd, &buf, sizeof(buf));
+ ASSERT_EQ(ret, sizeof(buf));
+ close(fd);
+ return path;
+}
+
+struct tracer_args_files {
+ char *path_orig, *path_hijack, *path_swap;
+};
+
+/* Move a file after the filter evaluation but before the effective syscall. */
+void tracer_swap_file(struct __test_metadata *_metadata, pid_t tracee,
+ int status, void *args)
+{
+ int ret;
+ unsigned long msg;
+ struct tracer_args_files *info = (struct tracer_args_files *)args;
+
+ ret = ptrace(PTRACE_GETEVENTMSG, tracee, NULL, &msg);
+ EXPECT_EQ(0, ret);
+ /* If this fails, don't try to recover. */
+ ASSERT_EQ(0x1002, msg) {
+ kill(tracee, SIGKILL);
+ }
+ /* Let's start the bonneteau! */
+ ret = rename(info->path_orig, info->path_swap);
+ EXPECT_EQ(0, ret);
+ ret = rename(info->path_hijack, info->path_orig);
+ EXPECT_EQ(0, ret);
+ ret = rename(info->path_swap, info->path_hijack);
+ EXPECT_EQ(0, ret);
+}
+
+FIXTURE_DATA(TRACE_swap_file) {
+ struct sock_fprog prog;
+ pid_t tracer;
+ struct tracer_args_files tracer_args;
+ char *path_orig, *path_hijack, *path_swap;
+};
+
+FIXTURE_SETUP(TRACE_swap_file)
+{
+ int fd;
+ unsigned long orig_delta, orig_size, hijack_delta, hijack_size;
+ struct sock_filter filter[] = {
+ BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
+ offsetof(struct seccomp_data, nr)),
+ BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_open, 0, 1),
+ BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1002),
+ BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
+ };
+
+ memset(&self->prog, 0, sizeof(self->prog));
+ self->prog.filter = malloc(sizeof(filter));
+ ASSERT_NE(NULL, self->prog.filter);
+ memcpy(self->prog.filter, filter, sizeof(filter));
+ self->prog.len = (unsigned short)ARRAY_SIZE(filter);
+
+ /* Create all the files */
+ self->path_orig = new_file(_metadata, "orig", 'O');
+ self->tracer_args.path_orig = self->path_orig;
+ self->path_hijack = new_file(_metadata, "hijack", 'H');
+ self->tracer_args.path_hijack = self->path_hijack;
+ self->path_swap = new_file(_metadata, "swap", 'S');
+ self->tracer_args.path_swap = self->path_swap;
+
+ /* Remove the temporary swap file */
+ unlink(self->path_swap);
+
+ /* Launch tracer */
+ self->tracer = setup_trace_fixture(_metadata, tracer_swap_file,
+ &self->tracer_args);
+}
+
+FIXTURE_TEARDOWN(TRACE_swap_file)
+{
+ teardown_trace_fixture(_metadata, self->tracer);
+ if (self->prog.filter)
+ free(self->prog.filter);
+ if (self->path_orig) {
+ unlink(self->path_orig);
+ free(self->path_orig);
+ }
+ if (self->path_hijack) {
+ unlink(self->path_hijack);
+ free(self->path_hijack);
+ }
+ if (self->path_swap) {
+ unlink(self->path_swap);
+ free(self->path_swap);
+ }
+}
+
+TEST_F(TRACE_swap_file, argeval_toctou_filesystem)
+{
+ int fd;
+ char buf;
+ ssize_t len;
+
+ /* Validate the first test file */
+ fd = open(self->path_orig, O_RDONLY);
+ EXPECT_NE(-1, fd) {
+ TH_LOG("Failed to open %s", self->path_orig);
+ }
+ len = read(fd, &buf, sizeof(buf));
+ EXPECT_EQ(1, len) {
+ TH_LOG("Failed to read from %s", self->path_orig);
+ }
+ EXPECT_EQ('O', buf) {
+ TH_LOG("Got unexpected value from %s", self->path_orig);
+ }
+ close(fd);
+
+ /* Validate the second test file */
+ fd = open(self->path_hijack, O_RDONLY);
+ EXPECT_NE(-1, fd) {
+ TH_LOG("Failed to open %s", self->path_hijack);
+ }
+ len = read(fd, &buf, sizeof(buf));
+ EXPECT_EQ(1, len) {
+ TH_LOG("Failed to read from %s", self->path_hijack);
+ }
+ EXPECT_EQ('H', buf) {
+ TH_LOG("Got unexpected value from %s", self->path_hijack);
+ }
+ close(fd);
+
+ apply_sandbox0(_metadata, self->path_orig);
+
+ /* Setup the hijack for every open */
+ EXPECT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER,
+ SECCOMP_FILTER_FLAG_TSYNC, &self->prog)) {
+ TH_LOG("Failed to install filter!");
+ }
+
+ /* Hijacked file */
+ fd = open(self->path_orig, O_RDONLY);
+ EXPECT_EQ(-1, fd) {
+ TH_LOG("Could open %s", self->path_hijack);
+ }
+ EXPECT_EQ(EPERM, errno);
+ close(fd);
+
+ /* Denied file */
+ fd = open(self->path_orig, O_RDONLY);
+ EXPECT_EQ(-1, fd) {
+ TH_LOG("Could open %s", self->path_hijack);
+ }
+ EXPECT_EQ(E2BIG, errno);
+ close(fd);
+}
+
+/*
+ * TODO: tests to add
+ * - symlink following
+ * - dentry/inode/device/mount checkers
+ * - PATH_BENEATH
+ * - object creation with nonexistent file
+ * - validate that ptrace's SETREGS is still working on a process using seccomp-objects
+ * - TOCTOU with a hard link (should pass)
+ * - limits
+ */
+
#endif /* SECCOMP_DATA_ARGEVAL_PRESENT */
/*
--
2.8.0.rc3
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